UNIVERSITE DE MAROUA
THE UNIVERSITY OF MAROUA
ECOLE NORMALE
SUPERIEURE
HIGHER TEACHERS’ TRAINING
COLLEGE
DEPARTEMENT DES
SCIENCES DE LA VIE ET DE
LA TERRE
DEPARTMENT OF LIFE AND
EARTH SCIENCES
The characterization of echolocation signals of
insectivorous bats in the Far-North region of
Cameroon
A Dissertation Submitted in Partial Fulfillment of the Requirements for the Award
of a MASTER’S II Diploma.
(Series: Zoology)
Presented by:
AARON MANGA MONGOMBE
B.Sc. (Hons) in Zoology, DIPES II in Life and Earth Sciences
Matriculation: 09B0605N
Directed by:
Dr. BAKWO FILS ERIC MOISE
University of Maroua
Dr. DAVID EMERY TSALA
University of Maroua
2011/2012 Academic year
i
The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
SIGNATURE
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
DEDICATION
This research work is dedicated to my mother
HANNAH MANGA ENYOWE
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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ACKNOWLEDGEMENTS
I thank the Almighty God for His Favour.
To Dr. DAVID EMERY TSALA Senior Lecturer at the University of Maroua
who took off time his busy schedule to supervise this research work, and also for his
suggestions, advices and encouragement;
My gratitude also goes to my Supervisor Dr. BAKWO FILS ERIC MOISE.
lecturer university of Maroua for his availability, for providing the equipment to carry out
this research work, for his advice, his support, encouragement and for introducing me
into the world of bat conservation;
To BOL A ANONG ALIMA GBERING for his participation during the field
work, recording and his advice;
To MMAE JACQUES PATRICK for his help during the fieldwork and for his
availability;
Special thanks go to the Head of Department and all lecturers of the Department of
Life and Earth Sciences for impacting us with knowledge and availability whenever we
needed them;
My sincere gratitude goes to the family of Mr. NCHIDA Leonard and AKERE
Raheal for their support, encouragement and advice during the realization of this
research work and throughout my stay in Maroua;
My deep appreciations go to my uncles Rev Dr. NJUMA MANGA WILLIAMS,
OSCAR MENYOLI MUAMBO. To my sister FRIDA MANGA NANYONGO. My
brother SIMON MANGA MWAMBO and his wife MISPA ZUH. To my cousins
MANGA SIEGFRED, ENJEMA MANGA, FRI MANGA, CARINE MANGA and
AKWI MANGA;
To NUBILA NABILA DORIS for her prayers and encouragement.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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TABLE OF CONTENT
SIGNATURE…………………………………………………………………………….
i
DEDICATION……………………………………………………………………………
ii
ACKNOWLEDGEMENT……………………………………………………………….
iii
TABLE OF CONTENT………………………………………………………………….
iv
ABSTRACT AND RESUME................................................................................................ viii
LIST OF TABLES………………………………………………………………………
ix
LIST OF FIGURES………………………………………………………………………
x
LIST OF ABBREVIATIONS……………………………………………………………..
xi
INTRODUCTION………………………………………………………………………..
1
CHAPTER I: LITERATURE REVIEW………………………………………………….
3
I.1 Justified classification of insectivorous bats………………………………………….
3
I.2 Anatomy of insectivorous bats………………………………………………………
6
I.2.1 External anatomy………………………………………………………………….
6
I.2.1.1Wings………………………………………………………………………………
6
I.2.1.2 Head……………………………………………………………………………….
7
1.2.1.3 Hind limbs and feet………………………………………………………………
7
1.2.1.4 Tail and interfemoral membrane…………………………………………………
10
I.2.2 Internal anatomy……………………………………………………………………
11
I.2.2.1 Skeletal system…………………………………………………………………..
11
I.2.2.2 Muscular system………………………………………………………………..
12
I.2.2.3 Nervous system………………………………………………………………….
13
1.2.2.4-Respiratory and cardiovascular systems……………………………………..,,,
13
I.3 Senses of bats……………………………………………………………………….
13
I.3.1Vision……………………………………………………………………………….
13
I.3.2 Taste and olfaction………………………………………………………………..
14
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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I.3.3 Echolocation and hearing…………………………………………………………
15
I.4 Echolocation………………………………………………………………………….
15
1.4.1 Principle of echolocation…………………………………………………………...
18
I.4.2 Functions of echolocation ………………………………………………………......
18
I.4.3 Information defined by echolocation………………………………………………
19
I.4.3.1Target size………………………………………………………………………….
19
I.4.3.2 Target speed………………………………………………………………………
20
1.4.3.3 Target distance ………………………………………………………………….
20
I.4.3.4 Horizontal or azimuthal position of target……………………………………….
21
I.4.3.5 Vertical position of target………………………………………………………..
21
I.4.3 Properties of bat echolocation calls……………………………………………….
22
I.4.3.1 Ultrasound…………………………………………………………………………
22
I.4.3.2 Pulses or signals………………………………………………………………….
22
I.4.3.3 Call phases………………………………………………………………………..
23
I.4.3.4 Acoustic features of bat echolocation signals……………………………………
23
I.4.3.5 Production time of echolocation calls……………………………………………
28
I.4.4 Production and emission of echolocation signals………………………………….
29
I.4.4.1 Auditory adaptation to perception of echolocation signals………………………
30
CHAPTER II: MATERIAL AND METHODS……………………………………………
33
II.1 Description of study area……………………………………………………………
33
II.1.1 Presentation of the town of Maroua……………………………………………….
33
II.1.1.1 Relief…………………………………………………………………………….
33
II.1.1.2 Climate…………………………………………………………………………..
33
II.1.1.3 Hydrography…………………………………………………………………….
34
II.1.1.4 Inhabitants………………………………………………………………………
34
II.2 Capture sites…………………………………………………………………………
34
II.2.1 Roost sites…………………………………………………………………………
34
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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II.2.2 Foraging and drinking sites………………………………………………………..
35
II.3 Methods of data collection and analyses……………………………………………
37
II.3.1 Capture of bats……………………………………………………………………
37
II.3.2 Identification of bats……………………………………………………………….
37
II.3.3 Anabat acoustic recording…………………………………………………………
37
II.3.4 Statistical analysis of data…………………………………………………………… 38
II.5.1.1 Calculation of sampling or capture effort………………………………………..
38
II.5 1.2 Analyses of echolocation calls…………………………………………………
39
II.5 1.2.1 Qualitative analysis of echolocation calls……………………………………
39
II.5 1.2.2 Quantative analysis of echolocation calls……………………………………
40
CHAPTER III: RESULTS AND DISCUSSIONS………………………………………..
42
III.1 Diversity and complementary indices………………………………………………
43
III.1.1Diversity ALPHA………………………………………………………………….
43
III.1.2 Diversity BETA…………………………………………………………………...
45
III.2 Qualitative analysis of echolocation calls…………………………………………..
46
III.2.1Characterisation of echolocation signals………………………………………….
46
III.2.2 Descriptive statistics of echolocation call parameters……………………………
61
III 3 Quantitative analysis of echolocation signal………………………………………..
67
III.3.1 Discriminant function analysis……………………………………………………
67
CONCLUSION AND PERSPECTIVES…………………………………………………
74
LITERATURE CITED……………………………………………………………………
75
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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ABSTRACT
In other to identify insectivorous bats by their echolocation signals in Maroua, we
captured 96 insectivorous bat belonging to 13 species and three families (Molossidae,
Vespertilionidae and Rhinolophidae) using Mist nets. Three species (Rhinolophus fumigatus,
Pipistrellus nanus and Chaerephon nigri) were captured for the very first time in Maroua,
increasing the total number of known species of insectivorous bats in Maroua to 18.
Echolocation call of each individual bat was recorded in flight after hand release using an Anabat
SD1 detector. The sonogram of each individual bat was displayed by Analook and categorized
into three call types (FM, FM/QCF and FM/ CF/FM) as a means providing a library of bat
vocalizations that could be used for qualitative acoustic survey and species identification.
Discriminant function analysis was applied to search phase calls of 65 individual bats belonging
to five species. Seven parameters calculated from each search phase call by Analook were used
to classify calls using Discriminant function analysis. This resulted in a correct overall
classification of 69.7%. The minimum frequency (Fmin) was the parameter that contributed the
most in differentiating bat calls. This work provide the first description of echolocation calls of
insectivorous bats in this region and offers a basis for future bats surveys in order to encourage
the development of locally customized conservation strategies.
Key words: Echolocation, Maroua, Cameroon, insectivorous Bat
RESUME
Dans le but d‟identifier les chauves-souris insectivores par leurs signaux d'écholocation.
Nous avons capturé 96 chauves-souris insectivores appartenant à 13 espèces et trois familles
(Molossidae, Vespertilionidae et Rhinolophidae) en utilisant un filet Japonais. Trois espèces
(Rhinolophus fumigatus, Pipistrellus nanus et Chaerephon nigri) ont été capturé pour la
première fois dans la région de Maroua, augmentant la richesse spécifique des chauves-souris
insectivores à 18. L‟écholocation de chaque chauve-souris a été enregistrée en utilisant la
méthode “hand release” à l‟aide d‟un détecteur Anabat SD1. Les sonagrammes de chaque
chauves-souris a été traite dans le logiciel Analook et ont été classe dans trois types de
fréquence (FM, FM/QCF et FM / CF/FM). Ces catégories des sons émis sont utilisées pour
identifier les espèces. L‟analyse Discriminant a été appliquée aux signaux enregistres de 65
chauves-souris qui appartenant à cinq espèces. Sept paramètres ont été utilisés pour classer ce
sont émis de 65 chauves-souris qui appartiennent à cinq espèces en utilisent l‟analyse
discriminant. Cela a permis de d‟obtenir une classification totale correcte de 69,7%. La
fréquence minimum (Fmin) a été le paramètre qui contribue le plus à différencier les sons émis
des différentes espèces. Ce travail fournit les premières descriptions son émis de l'écholocation
de chauve-souris insectivores dans cette région et offre une base pour les futures études des
chauves-souris insectivore afin d'encourager le développement de stratégies de la conservation
locale.
Mots clés : Echolocation, Maroua, Cameroun, Chauves-souris insectivore.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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LIST OF TABLES
Table 1:
Geographical coordinates of capture and acoustic monitoring sites and the
number of sessions…………………………………………………………
Description of the 10 call parameters calculated by software Analook
35
calculates from each call…………………………………………………….
40
Number of individuals captured per site, capture effort and capture success
Comparison of two complementary indices of Jaccard Classic and
42
Sorensen Classic…………………………………………………………….
45
Table 5:
Summary of echolocation frequency used by insectivorous bats in Maroua.
65
Table 6:
Table 7:
Descriptive statistics for echolocation parameters of 13 species of
insectivorous bats in the far-north region of Cameroon…………………….. 66
Test of homogeneity of variance……………………………………………. 67
Table 8:
Relative power of Discriminant Functions………………………………….
68
Table 9:
Wilks‟ lambda table………………………………………………………..
69
Table 10: Structure matrix table………………………………………………………
69
Table 11: Classification table………………………………………………………….
70
Table 2:
Table 3:
Table 4:
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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LIST OF FIGURES
Figure 1: Illustration of the wing of a bat……………………………………………
Figure 2: Tendons in the foot of bats helps to keep the claws firmly hooked to the
perch by utilizing the weight of the hanging bat…………………………
Figure 3: Tails and uropatagium of (A) molossid bat (B)Vespertilionid bat………..
8
Figure 4: The skeleton of a bat………………………………………………………
Figure 5: Variation of ear of insectivorous bats ( A)Vespertilionid bat with a tragus
and no antitragus (B) Molossid bat with an antitragus but greatly reduced
tragus………………………………………………………………………
Figure 6: Faces of insectivorous bats showing: A Rhinolophid bat with a
horseshoe-shaped nose leaf B molossid bat with prominent ridge muzzle.
C Vespertilionid with a simple muzzle …………………………………
Figure 7: Echolocation in bats………………………………………………………
12
Figure 8: Determination of target size by echolocating bats………………………
19
Figure 9: Determination target speed by echolocating bats…………………………
20
Figure 10: Determination target distance by echolocating bats………………………
20
Figure 11: Determination of horizontal position of target by echolocating bats…….
21
Figure 12: Determination of vertical position of target by echolocating bats………..
21
Figure 13: Features of a generic call pulse……………………………………………
23
Figure 14: Typical echolocation call shapes………………………………………….
23
9
10
16
17
18
Figure 15: Phase transition in echolocating bats…………………………………………. 24
Figure 16: Types of bat echolocation calls and example of bats that produce them….
26
Figure 17: Schematic illustration of the anatomy of the vocal membrane……………
29
Figure 18: The schematic plan of the mammalian ear and sound wave flow from the
pinna to the inner ear…………………………………………………………... 32
Figure 19: Capture sites for insectivorous bats in Maroua Cameroon………………
36
Figure 20: Anabat SD 1 bat detector…………………………………………………
38
Figure 21: Accumulation curve of insectivorous bat species sampled in the town of
Maroua……………………………………………………………………
44
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Figure 22: Sonogram of Chaerephon major in flight after hand release (F7, compressed)… 48
Figure 23: Sonogram of Chaerephon nigri in flight after hand release (F7, compressed)….. 49
Figure 24: Sonogram of Chaerephon pumilus in flight after release from hand (F8,
compressed)……………………………………………………………………… 50
Figure 25: Sonogram of Mops condylurus in flight after hand release (F8, compressed)…..
51
Figure 26: Sonogram of Mops niveiventer in flight after hand release (F7,
compressed)…………………………………………………………………….. 52
Figure 27: Sonogram of Nycticeinops schilieffeni in flight after hand release (F5,
compressed)……………………………………………………………………… 53
Figure 28: Sonogram of Pipistrellus nanus in flight after hand release (F9, compressed)…. 54
Figure 29: Sonogram of Pipistrellus nanulus release from hand (F9, compressed)…
55
Figure 30: Sonogram of Pipistrellus inexpectatus in flight after hand release (F7,
compressed)……………………………………………………………………… 56
Figure 31: Sonogram of Scotoecus hirundo release from hand (F7, compressed)………….. 57
Figure 32: Sonogram of Scotophilus dinganii in flight after hand release (F7,
compressed)……………………………………………………………………..
Figure 33: Sonogram of Scotophilus leucogaster in flight after hand release (F8,
compressed)……………………………………................................................
Figure 34: Sonogram of Rhinolophus fumigatus in flight after hand release (F6,
truetime)………...........................................................................................
Figure 35: Average maximum, minimum frequencies and duration of echolocation
call for Chaerephon major, Chaerephon pumilus, Mops condylurus and
Mops niveiventer………………………………………………………………..
Figure 36: Average maximum and minimum frequencies of echolocation call for
Scotophilus dinganii and Scotophilus leucogaster………………………
Figure 37: Canonical discriminant function plot……………………………………...
Masters II Dissertation, University of Maroua (E.N.S)
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58
59
60
62
64
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
LIST OF ABBREVIATIONS
DFA: Discriminant function analysis
KHz: Kilohertz
DSC: Doppler shift compensation
FM: Frequency modulation
C F: Constant Frequency
QCF: Quasi-constant frequency
IUCN: World Conservation Union
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
INTRODUCTION
Bats are nocturnal animals and the only mammals that have evolved true flight. At
present there are about 1,232 extant species of bats representing about a quarter of all
known mammal species (Schipper et al., 2008). They are second after rodents in terms of
abundance (Altringham et al., 2006).They play a vital ecological role on Earth, as seed
dispersers and insect predators (Patterson et al., 2003). The Order Chiropterais divided
into two groups, frugivorous and insectivorousbats (Koopman, 2003). The frugivores
comprise about 187 species (IUCN, 2010). The insectivoresare the largest and most
ecologically diverse group with about 963 species described (IUCN, 2010). They are
wide spread throughout the world, except for the arctic, antarctic and some isolated
islands (Simmons, 2005). The greatest diversity occurs in the tropics (Willig and selcer,
1989).
The ecological success of insectivorous bats is based on numerous morphological,
physiological and behavioral adaptations, which permits them to have access to a wide
range of habitats and resources at night (Schnitzler and Kalko, 2001). Echolocation is one
of the adaptations that make bats so ecologically successful (Schnitzler and Kalko,
2001).Echolocation involves the active transmission and reception of ultrasonic calls that
allow bats to essentially “see” with sound. The ability to echolocate is present in all
insectivorous bats but is limited to the genus Rousettus of the frugivorous bats (Schnitzler
and Kalko, 2001).Insectivorous bats use echolocation for orientation and foraging, but it use
and importance is highly variable (Neuweiller, 1989; 1990; Fenton, 1999). They use
echolocation to capture and feed on airborne nocturnal insects and other arthropods (Kunz et
al., 2011). They suppress insects such as agricultural pest species and insects that annoy or
transmit specific pathogens to humans and other mammals (Kunz et al., 2011). In doing
so, they contribute to the maintenance of ecosystem stability.
Despite their abundance and ecological importance, bats are under significant
threat throughout the world (Papadatouet al., 2008). One of the least appreciated threats
to bats is lack of information. Of the 963 species of insectivorous bats, only a few have
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
been well-studied (Papadatou et al., 2008). There is little information about their
distribution, roosting and habitat requirement for most species, making assessing which
species is threatened or in need of special conservation measures difficult. This difficulty
may partly be due to old method of study which mainly involved capture /or observational
techniques. Ultrasonic detectors are now widely used to study habitat use by bats (Walsh and
Harris, 1996; Vaughan et al., 1997). Detectors often determine presence of more species at a
site than capture techniques (Murray et al., 1999) and can be deployed in a much wider
variety of locations than capture techniques (O‟Farrell et al., 1999b). They can also be
operated remotely to permit simultaneous sampling, thereby increasing comparability among
sites. Bat detectors can be used to accurately identify bats (Vaughan et al., 1997; O'Farrell et
al., 1999b; Parson and Jones, 2000).Field identification usually begins with the establishment
of a library of reference calls from individual species, specific to the locality, since
intraspecific geographical variations may occur (Barclay et al., 1999; O‟Farrell et al., 2000).
In Cameroon, few studies have been carried out on the inventory of bats in the forest
zone (Allen, 1952; Bakwo, 2009a, 2009b, 2010). An inventory on bats in the far-north
region and Maroua in particular was carried out by Bol et al., (2011). However, no
previous study on species identification based on acoustic parameters has been carried
out anywhere in the country. This accounts for the total absence of echolocation reference
call libraries.
This work therefore has as main objective to record representative echolocation calls of
some insectivorous bats in the town of Maroua. More specifically;
 to capture and identify insectivorous bats;
 to register their echolocation calls using an Anabat SD 1 ultrasound detector;
 to make reference recordings of known species;
 to determine the range of frequency at which some insectivorous bats in Maroua
emit their echolocation calls;
This data obtained shall help to facilitate the further study of insectivorous bats without
the need for capture.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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CHAPTER I. LITERATURE REVIEW
I.1 Justified classification of Insectivorous bats
 Kingdom Animalia
-cells without cell wall or plastids;
-multicellular eukaryotes with heterotrophic nutrition.
 Phylum Chordata
-presence of dorsal notochord or vertebral column;
-the presence of a hollow dorsal nerve chord.
 Subphylum Craniata
-skull surrounds a well-developed brain;
-a skeleton made up of cartilage or bone.
 Super class Tetrapoda
-two pair of pentadactyl limbs;
-presence of jaws.
 Class Mammalia.
-the presence of only the left systemic arch;
-milk secretion by mammary glands.
 Subclass Placentalia
-embryo develops in the maternal uterus;
-cerebral cortex larger and more complex.
 Order Chiroptera (Rosevear, 1965).
-forelimb with elongated digits modified for flight and joint together by a
membrane extending to the side of the hindlimb;
-knee of hindlimb directed posteriorly due to rotation of hindlimb for support of
wing and tail membrane.
 Frugivorous bats.
-second digit of forelimb clawed and relatively free of the third digit;
-simple pinna with inner margin forming a complete ring around ear opening.
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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 Insectivorous bats.
-second digit of forelimb is clawless and fully enclosed in wing membrane;
-theinner margin of pinnadoes not form a complete ring around ear opening.
 Family Emballonuridae.
- free terminal portion of tail emerges dorsally from near middle of interfemoral
membrane forming a sheath;
-sac-shaped gland in the wings membrane anterior to the elbow join in some.
 Family Craseonycteridae.
-muzzle swollen laterally, terminating in vertical pad, which is surrounded by a
ridge-like outgrowth.
- complete absence of a tail.
 Family Rhinopomatidae.
-the tail is nearly as long as the head and body combined;
- fur lacking on the face and posterior portion of the abdomen.
 Family Nycteridae.
-large ears longer than head;
-muzzle with deep central longitudinal slits or hollow fleshy noseleaves.
 Family Megadermatidae.
- large ears connected across the forehead by a ridge of skin;
- large erect nose-leaf.
 Family Rhinolophidae.
-tail included within interfemoral membrane to the tip;
-posterior nose leaf sub triangular with an erect point.
 Family Hippossideridae
-tail included within interfemoral membrane to the tip;
-posterior nose leaf elliptical.
 FamilyMormoopidae.
-presence of a conspicuous leaf-like flap of skinon the chin (chinleaf);
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
-small fold around the nostril and around the mouth forming a funnel into oral
cavity.
 Family Noctilionidae.
-muzzle is flat, with extensively cleft lips hanging on each side and extending up
to the nostril;
-hindlimb and hindfeet withlarge, curved claws.
 Family Phyllostomidae.
-ears are usually narrow and pointed;
-diverse method of feeding including feeding on fresh blood.
 Family Thyropteridae.
-circular adhesive disc or sucker shaped cup at base of the thumb and on the sole
of the feet;
-third and fourth toes are fused.
 Family Myzopodidae.
-sessile disc on thumb and soles of feet;
-free terminal portion of tail stout, and approximately equal in length to that in the
membrane.
 Family Furipteridae.
-atrophied and functionless thumb, entirely enclosed in the membrane in front of
the forearm;
-large funnel-shaped ears, base of the ears cover the eyes.
 Family Natalidae.
-adult males have a bulbous natalid organ of unknown function lying just below
the skin of the forehead;
-large funnel shaped ears.
 Family Mystacinidae.
-well-developed limbs adapted for quadrupedal locomotion, feet and thumb
possesses sharp claws and a secondary talon at its ventral base;
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
-ears are separate and the tragus is long and pointed.
 Family Molossidae.
-first andfifth digits of feet with fringe of stiff bristles;
-upper lips gathered into a number of vertical folds.
 Family Vespertilionidae.
-long tail is included within interfemoral membrane to the tip;
-muzzle without nose leaf.
I.2 Anatomy of insectivorous bats
Bats are mammals as such, they possess the entire features characteristic of this
vertebrate class (Hill and Smith, 1984). However, because of their adaptation to flight,
they possess an easily recognizable form and appearance. The wing is the most obvious
adaptation of a bat. Unlike birds in which the bony structure of the wing consists of
greatly modified forelimb bones, the wing skeleton of bat is in comparison not much
different from that of the forelimb of most mammals (Hill and Smith, 1984).
I.2.1 External anatomy
The wing and the flight membrane constitute perhaps most obvious external
feature of this special group of mammals.
I.2.1.1Wings
The wing consists of elongated hand and finger bones which are connected to each
other by a flexible membrane. The short thumb which is often independent of the
membrane points forward, and possess a claw used in locomotion, food handling and
fighting. The second to the fifth fingers are clawless and constitute the major support for
the membrane. The membrane extends on each side from the shoulder in front of the
upper arm and forearm round the wrist to the index finger. It continues from fifth finger
to the flanks and ankle of the legs. Depending on the species, there may or may not be a
flight membrane connecting the hindlimbs and the tail (Hill and Smith, 1984;
Altringham, 1996) (Fig 1). Muscles and blood vessels traverse this membrane. It also
carries a tissue of elastic fibres, which contract when the fingers are at rest.
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Figure 1: illustration of the wing of a bat Hill and Smith(1984)
I.2.1.2Head
Bats display a wide range of variation in the shape of the head more than any other
mammal (Hill and Smith, 1984). Generally, insectivorous bats have moderately long
pointed noses. The back part of their heads is rounded in appearance. The wider range of
variation is correlated to their different diets and food capture methods. The shapes of
their skulls vary according to their diet (Hill and Smith, 1984).Variations exist among
this group. The insectivorous bats that eat soft-bodied insects such as moths and
mosquitoes have slightly, longer and shallow muzzles or their faces may be short and
broad. Bats that eat hard-bodied insects like beetles have shorter and deeper muzzles. The
back of their head is wide and highly domed. This appearance is associated with the crest
or ridges or a great-expanded braincase (Hill and Smith, 1984).
Carnivorous bats generally have dog-like shaped heads. Others are less dog-like and have
long, stout muzzles and long round heads (Hill and Smith, 1984). The piscivorous bats
have short, deep faces and high-domed heads like bulldogs. The snouts may be long,
deep and pointed, or extremely short with high doming of the braincase (Hill and Smith,
1984).
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The fruit-eating microchiropterans such as Phylostomatidae, the snout is long,
deep, and pointed. The rear portion of the head widely rounded. This head shape provides
room for the massive grinding teeth. Some frugivorous bats show a trend toward the
extreme shorting of the face and high doming of the brain case (Hill and Smith, 1984).
In some bats such as phyllostomatids, the face is very broad and nearly flat and the back
of the head rises sharply above the level of the eyes (Hill and Smith, 1984). Bats that eat
nectar and pollen have long and tubular muzzles suited for reaching deep into flowers.
The back of their head is low and rounded. There is a wide variation in the length of the
snout (Hill and Smith, 1984).
In addition to the dietary habit, which reflect shape of the head of bats, other
consideration such as aerodynamics and roosting habit may influence shape of head.
Swifter-flying bat species tend to have fusiform head. The slow-flying bats tend to have a
wider range of head shapes that are less restricted to aerodynamic forces (Hill and Smith,
1984). The roosting habit of occupying narrow rock crevices or hollow internodes of
bamboo is associated with the trend of flattened head (Hill and Smith, 1984).
1.2.1.3 Hind limbs and feet
The hindlimb of bats is very specialized. The upper leg bone, the femur has been
rotated 180◦ from it normal position in other terrestrial vertebrates. It is now directed
rearward. This arrangement enables the attachment of the wing and the interfemoral
(uropatagium) membranes to the hindlimb (Hill and Smith, 1984). It facilitates steering
during flight and the head down roosting posture. It also coordinated control of this flight
membrane. The lower section of the hind limb is composed almost entirely of the tibia.
The fibula is vestigial (Hill and Smith, 1984). The species that move about on the ground
have slightly stouter legs than those species that do not. The feet of bats are usually small.
Five toes are present. The toes are long and terminate in strong, sharp recurved claws.
Bats generally hang by one or both feet, using the sharp recurved claws of the five toes to
support their weight. In fish eating microchiropteran bats, the feet are usually large and
the toes are compressed laterally and terminate with large claws. These are adaptations
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for seizing and holding prey (Hill and Smith, 1984). The whole limb can rotate through a
wide angle allowing hanging bats to swivel through a circle. The toes of the hind limbs
all have strong laterally compressed claws. Some bats have developed an extra bone on
the hindlimbs near the ankle (Hill and Smith, 1984). The tendons in leg and feet of bats
are organized in such a way that the suspended weight of the hanging bats causes the toes
and claws to grip the foothold in the roost firmly even if the animal is sleeping (Hill and
Smith, 1984) (Fig 2). Except in the sucker-foot bats; family Thyropteridae and
Furipteridae, bats possess special locking tendons in the toes, which allow bats to hang
without expending energy (Bennett, 1993) (Fig 2).
Another structure associated with hindlimb is the calcar(Fig 1). The calcar is a
long cartilaginous structure that articulates with heel bone (calcaneum) and is bound in
the uropatagium. The function of the calcar is to support the trailing edge of the
interfemoral flight membrane (Hill and Smith, 1984). Calcar can also be used to make
camber changes in the uropatagium during flight. The degree to which the calcar is
developed in different species is variable. The fishing species have very long calcar while
the Rhinopomatids have no calcar. Fig 2 illustrates the organization of tendons in the feet
of bats, which help them to firmly grip the perch.
Figure 2: Tendons in the foot of bats helps to keep the claws firmly hooked to the perch by
Utilizing the weight of the hanging bat (Hill and Smith, 1984)
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1.2.1.4 Tail and interfemoral membrane
Most bats have a tail. There is considerable variation in the structure of the tail in
insectivorousbats. Some species such as rhinopomatids have very long and threadlike
tails. These tails are roughly equal to the length of their body and largely free from a
narrow interfemoral membrane (Hill and Smith, 1984) .The Molossids have a tail that has
at least half of the tail protruding from rear margin of the uropatagium (Fig.3A). Members
of the family Vespertilionidae also possess a characteristic long tail .The long tail in this
case is completely enclosed within the relatively large uropatagium (Fig.3B). Similar
conditions are found in the rhinolophids, hipposiderids and in some megadermatids. In
mormoophids, the tail protrudes from the dorsal surface of the interfemoral membrane.
The tail may be short or absent in some species. Members of the family Craseonycteridae
have an extensive uropatagium but lack any remnant of a tail. In the Phyllostomatids,
there is a considerable variation in the length of the tail and the form of the uropatagium.
Figure 3: Tails and uropatagium of (A) molossid bat (B) Vespertilionid bat (Dietz, 2005)
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I.2.2 Internal anatomy
Like other mammals, bats possess the different organ-systems of the body. In most
cases, these systems are specialized due to the acquisition of flight.
I.2.2.1 Skeletal system
Bats have all the basic anatomical structures associated with mammalian skeleton.
However, the acquisition of flight has led to many of the structures of the skeleton
becoming highly modified (Hill and Smith, 1984). The most obvious changes are the
greatly elongated bones of the fore limbs, particularly the metacarpals and phalanges (Fig
4). The degree of elongation becoming greater as one moves further away from the body.
The bones of the thumb, the only digit capable of free movement are not greatly
elongated. The ulna is greatly reduced and often fused to a strong radius, which support
the wing. The wrist is highly flexible allowing the wing to be folded down. Only the
thumb possesses a claw (Hill and Smith, 1984).
Apart from modifications related to the structure of wing and hindlimb. The axial
skeleton also shows adaptation and specialization unique to bats. The form of the cranium
varies amongst insectivorous bats. The form is directly related to the feeding habit and
food type. The most obvious feature of the cranium is the dentition. Insectivorous bats
like other mammals have a differential set of teeth. All the teeth except the molars are
deciduous (Hill and Smith 1984).The milk teeth are highly specialized. These specialized
teeth enable young bats to cling to the mother‟s breast while she is carrying her offspring
in flight. All bats have a full complements of canines. Modification in dental formulae
only involves the other type of teeth. Another modification that can be found in the
midline of the cranium is the sagittal crest. It is well developed in carnivorous and bats
that eat large beetles. The crest provides an increase in surface area for the attachment of
muscles (Hill and Smith, 1984). The postcranial skeleton also show modification related
to flight. The bodies of bats are relatively short (Fig 4). In general bats possess seven
cervical vertebrae, eleven thoracic vertebrae, four lumber vertebrae, and between zero
and ten caudal vertebrae. In some species, the last cervical and first thoracic vertebrae are
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fused. These fusions promote rigidity and limits movement of the main body axis, which
facilitates flight. The rib cage of bats is proportionately larger than those of other
mammals. They are also considerably broader and deeper than those of other mammals
are (Fig 4). The sternum in most bats is T-shaped (Fig 4). The scapula is roughly
triangular, these presumably to accommodate the attachment of flight muscles. The
pelvic girdle is also more strongly fused than in other mammals (Hill and Smith, 1984).
Overall, the major modification to the chiropteran skeletal system involves the reduction
in size and thickness of the skeletal elements and the promotion of a sturdy and
lightweight support system for flight (Hill and Smith 1984).
Figure4: The skeleton of a bat (Hill and Smith, 1984).
I.2.2.2 Muscular system
The muscular system of bats is highly adapted for flight (Altringham, 1996). The
musculature is typically mammalian, and highly aerobic. There are five major down
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stroke muscles and two major upstroke muscles. Bats possess five muscles that do not
occur in any other mammals (Hill and Smith, 1984).
I.2.2.3 Nervous system
The brain of bats is variable in size and seems to be closely associated with size.
Other variation in the brain relate to differences in diet, locomotion and mode of
orientation (Hill and Smith, 1984). Generally, the hindbrain is well developed in
insectivorous bats while the forebrain is enlarged in frugivorous bats. The forebrain
consists of the olfactory lobes and the neocortex. Frugivorous bats have a neocortical
region, but it is less well developed. Frugivorous bats have a rather large hindbrain when
compared to insectivorous bats. The hindbrain harbors the nerve center associated with
acoustic orientation (Hill and Smith, 1984). In addition, most of the motor control center
for flight is house here. In most insectivorous bats (except Phyllostomatids) the old
factory lobe is very small. The spinal cord of bats is also greatly shortened (Hill and
Smith, 1984).
1.2.2.4 Respiratory and cardiovascular systems
Their respiratory and cardiovascular systems are very adapted to flight. In flight,
the oxygen consumption per kg per time unit is approximately twice that of running
mammals, and is comparable to flying birds. When a bat takes off, its breathing rate
rapidly increases to match its wing beat frequency. The heart of a bat is about three times
larger than that of a terrestrial mammal of comparable size. This is to enable the
circulatory system pump around the body, the oxygen required for sustained flight.
I.3 Senses of bats
Insectivorous bats possess six senses including echolocation, touch, hearing,
vision, olfaction and taste.
I.3.1Vision
Most bats have well developed eyes, comparable in sensitivity to those of other
mammals. Most insectivorous bats rely almost exclusively on acoustic orientation;
therefore they turn to have rather small eyes. Vision plays a supplementary role in the
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daily lives of insectivorous bats. Considerable differences exist in both eye size and
morphology across species, reflecting a great ecological diversity (Chase, 1972; Hope
and Bhatnagar, 1979a, 1979b; Marks, 1980; Suthers and Bradford, 1980; Bell and
Fenton, 1986). In general, the eyes of frugivorous and nectarivorous microchiropterans
are larger than those of the insectivorous species. In addition, species that roost in caves,
mines and other darkened habitat rely mostly on hearing and echolocation for prey
detection and orientation. They have smaller eyes than those that roost in foliage and
open roosting situation (Chase, 1972).
Generally, the eyes of bats are adapted for nocturnal conditions in that their retina
consists almost entirely of rods (Chase, 1972; Marks, 1980; Pettigrew et al., 1998). They
have large corneal surfaces and lenses relative to the size of the eye. They also have
relatively large receptor fields, which give them good light gathering power at the
expense of acuity (Suthers, 1970; Suthers and Wallis, 1970). Bats can easily detect small
differences in brightness on clear nights, and the visual acuity remains relatively good in
dim illuminations. Most insectivorous bats have a short focal distance and hence a great
depth of focus (Suthers and Wallis, 1970).
Vision in insectivorous bats function mostly in the regulation of daily activity
rhythms, seasonal reproductive cycles and predator surveillance especially among tree
roosting species (Suthers, 1970). It is also important for detecting objects beyond the
relatively short detection range of echolocation and thus it can be used for orientation
during flight (Suthers and Wallis, 1970).
I.3.2Taste and olfaction
As with other mammals, olfaction along with taste is important to bats (Suthers,
1970). Bats have well developed taste receptors, olfactory epithelium, and olfactory
bulbs. In addition to this, many species have large vomeronasal organs, each with
specialized ducts connecting to the mouth and buccal cavity (Bhatnagar, 1980). These
paired organs pump chemicals containing dissolved chemicals to mouth cavity.
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Highly developed sense of smell and taste allow bats to distinguish food sources
(Suthers, 1970), recognize conspecifics during courtship and mating (Bradbury, 1977a,
1977b), promote mother-pup interactions (Suthers, 1970), and perhaps help identify
roost sites. Insectivorous bats rely on odor and taste to detect and ultimately select their
prey. In addition, some have facial and skin glands that produce secretions that has
important social functions including scent marking of objects and conspecifics
(Bradbury, 1977b).
I.3.3 Echolocation and hearing
Bats primarily use echolocation for foraging. It can also be used to detect obstacles
and to find roost sites. All species of microchiropterans seem to use echolocation for
orientation and prey capture, but it use is highly variable (Neuweiller, 1989).
Echolocation in insectivorous bats is aided by structures that are located on the ear and
nostrils. Insectivorous bats display a wide range of variation in ear shapes and sizes. Most
of their ear is composed of large flap-like external pinna. The base of the pinna is open at
the front and those not form a complete ring. The inside of the pinna bears transverse
ridges (Fig 5). These ridges provide structural support for the pinna (Hill and Smith,
1984). They are also involved in the collection of certain sound frequencies. The pinnae
are especially important to species that rely on hearing for orientation and to detect prey
(Orbst et al., 1993). Insectivorous bats possess two other ear components that assist them
in echolocation; the tragus and antitragus (Vaughan, 1986).The tragus is a fleshy
projection on the anterior edge of the ear opening (Fig 5A). The tragus is absent in some
species such as rhinolophids and hipposiderids and greatly reduced in molossids. In other
insectivorous bats, it is moderate to well develop. Tragus aid echolocating bats in
horizontal discrimination of the target (Lawrence and Simmons, 1982). The second ear
component is the antitragus. The antitragus is a broad flap that is continuous with the
outer margin of the pinna (Hill and Smith, 1984) (Fig 5B). It is well developed in
gleaning bats such as rhinolophids, hipposiderids and molossids, which take prey from
the surface by listening to the low frequency rustling noise made by prey (Hill and Smith,
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1984). The shape of the ear also varies among insectivorous bats. Some species such as
vespertilionids have relatively simple ears (Fig 5A). Others such as the Natalids possess
funnel shaped ears with generally blunt tragus. Rhinopomatids and some others have
simple but broadly rounded and cup-shaped ears. A number of microchiropterans such as
megadermatids have exceptionally long ears. The ears of the molossid bats lies forward
nearly parallel to the long axis of head and body (Fig 5B) (Hill and Smith, 1984). In
addition to echolocation, bats also use ears for maintaining equilibrium and detecting
audible sound. Detection of audible sound allows bats to locate and capture potential prey
(Bell, 1982; Fenton, 1990) and to communicate during courtship (Bradbury, 1977b;
Fenton, 1985). It is also used in mother-pop recognition (Balcombe and McCracken,
1992) as well as to increase their awareness to approaching predators (Hanson, 1970).
Figure 5: Variation of ear of insectivorous bats (A)Vespertilionid bat with a tragus and no
antitragus (B) Molossidbat with an antitragus but greatly reduced tragus(Dietz, 2005)
The nose possesses noseleaves that aid in echolocation. The noseleaves are
membranous outgrowth that surround and project upward from the nostrils (Arita, 1990).
They help in the transmission of echolocation (Hartley and Suthers, 1987). Species that
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use echolocation for detecting prey have more developed noseleaves than frugivorous,
nectivorous and vampire species that rely on echolocation mostly for orientation (Arita,
1990). In rhinolophids and hipposiderids, the noseleaves are similar in appearance. They
consist of a single blade-like nose leaf which arise from a fleshy plate that surrounds the
nasal aperture and stand erect behind this opening (Fig 6A). These noseleaves may be
long, short, slender or broad. In the true blood sucking bats family Phylostomatidae, the
noseleaves have been greatly reduced. The function of all noseleaves is to direct the
acoustic orientation of sound that the bat produces.
In mormoophids bats, the lips and chin region are ornamented with complex
foliations called chin leaf. This foliations function in directing the acoustic orientation
sound or they may augment the funnel shape of the mouth thus facilitating the capture of
insects as the bats flies through air.
Figure 6: Faces of insectivorous bats showing: A Rhinolophid bat with a horseshoe-shaped nose
leaf B molossidbat with prominent ridge muzzle.C Vespertilionid with a simple muzzle (Dietz,
2005)
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I.4 Echolocation
1.4.1Principle of echolocation.
Echolocation is based on the emission of ultrasound and the analyses of the
returning echo to detect localize and characterize the reflected target (Schnitzler et al.,
2001) (Fig 7). Insectivorous bats produce ultrasound through their larynx and emit them
from the mouth or via their nose. The only two genera of frugivorous bats that echolocate
produce ultrasound differently; Rousettus by clicking their tongueand Eonycteris by
clapping their wings. The ears perceive the returning echoes. The brain then interprets the
information, enabling the bats to obtain an auditory representation of their surrounding
(Suga, 2001).
Figure 7: Echolocation in bats (Source; Bat Conservation International, Course Booklet portal,
Arizona, Retrieved 02-05-2012 from http//www.batcon.org.
I.4.2Functions of echolocation
Insectivorous bats use echolocation for food acquisition that is, to detect,
categorize and localize their prey, for spatial orientation and to navigation from one place
to another. Echolocation can also be used to localize a perch, and to avoid obstacles
(Schnitzler et al., 2001). It has also been suggested that echolocation calls may also have
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a communicative function, for instance between roost members. Echolocation calls are
species specific and known to differ between the sexes, colonies and individuals for some
species. Individual bats within a species may vary their echolocation calls with
geographical location (Russo et al., 2007) habitat type, (Barclay et al., 1999) stage of
foraging (Parsons et al., 1997), and presence of and proximity to conspecifics (Obrist et
al., 1995). Call structure can also vary by gender, and may change as individual bat ages
(Jones et al., 2001; Murray et al., 2001; Russo et al., 2001). This means that reference
calls recorded in a particular region or particular habitat type cannot be applicable to
other regions, or other habitat type. Therefore, as far as possible species identification
methods should be developed in region and habitat types where they are to be used.
I.4.3-Information defined by echolocation
Echolocation does not only enable bats to orientate themselves or to avoid
obstacles. It also enables them to obtain different useful information about their target
thus procuring them with precise „acoustic vision‟. Bats use the returning echoes to
determine the following parameters of their target (Moss and Schnitzler, 1995);
I.4.3.1 Target size
The bat gets the size of an object from the intensity of echoes (Simmons and
Vernon, 1971). Larger targets have larger echo amplitude. However, amplitude by itself
is not enough information, because the echo amplitude is also larger when the target is
closer. Therefore, the bat compares echo amplitude to echo delay. A quiet echo at a short
delay must be a small, close object. If the same quiet echo has a long delay, it must come
from a large object further away (Moss and Schnitzler, 1995).
Figure 8: Determination of target size by echolocating bats (Nyssen, 2008)
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I.4.3.2 Target speed
The velocity of a target is gotten from the Doppler shift of the echoes (Schnitzler,
1968). Bats compute relative velocity by taking advantage of the Doppler shift. A
constant frequency sound coming toward you sounds higher than if it were stationary,
and sounds lower if it is going away from you. When the bat hears an echo at a higher
frequency than the call it emitted, it knows it is gaining on its target. Likewise, an echo at
a lower frequency than the emitted call means the target is outdistancing the bat (Fig 9).
In CF call, the long constant frequency pulse permits a very sensitive analysis of tiny
shifts in that frequency
Figure 9: Determination target size by echolocating bats (Nyssen, 2008)
I.4.3.3Target distance
The distance between the bat and an object is determined from the time delay
between the outgoing sound and the returning echo (Hartridge, 1945; Simmons, 1973).
Figure 10 shows the late return of echo from a distant object and the rapid return of echo
from nearby object (Fig 10).
Figure 10: Determination target distance by echolocating bats (Nyssen, 2008).
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I.4.3.4Horizontal or azimuthal position of target
The horizontal position of an object in space is determined by differences in the
intensity and/or time of arrival of echoes at the two ears (Fig 11).
Figure 11: Determination of horizontal vertical position of target by echolocating bats
(Nabet, 2005)
I.4.3.5 Vertical position of target
The vertical position is resolved by analyzing secondary echoes, which follow
different paths through the inner ear and around the tragus, depending upon their
direction of origin. The tragus thus plays an important role in resolving vertical position
of the target. It is responsible for generating multiple reflections in the external ear as
echoes travel to the eardrum (Lawrence and Simmons, 1982). The reflections of sound
waves from tragus and the wall of the pinna create interference patterns, which change
according to the vertical direction of the sound (Fig 12).Bats that lack tragus such move
their pinnae pattern correlating this with the emission of echolocation calls: one ear
moves upward and downward, the second ear moves forward and back. This pinnae
movement plays a role in sound localizations at the vertical plane (Neuweiler, 2000).
Figure 12: Determination of vertical position of target by echolocating bats (Nabet,2005)
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Together, these cues provide the bat with information to form a three-dimensional 3D
representation of a target and its position in space.
I.4.3Properties of bat echolocation calls
I.4.3.1 Ultrasound
Echolocation calls are ultrasounds. Ultrasound normally indicates sound frequency
above 20 kHz, which are inaudible to humans. The upper frequency human can “hear” is
limited to 18 kHz to 20 kHz. Most of echolocation calls are inaudible, with few
exceptions.
I.4.3.2 Pulses or signals
Bats emit echolocation sounds in pulses (Altringham, 1996). A bat call usually consists
of a series of sound pulses repeated at regular intervals. A consecutive string of pulses
made by the same bat is referred as a sequence (Corben and O‟Farrell, 1999, Reinhold et
al., 2001).A pass is defined as a continuous sequence of calls from a single bat from the
time it is first detected until it has travelled beyond the range of detection (Corben and
O‟Farrell 1999). Bats produce a wide range of different shaped pulses. The pulses vary in
properties depending on the species and can be correlated with different hunting
strategies and mechanisms of processing information (Grinnell, 1995).
There are four main parts of a bat echolocation pulse:
-the initial section. This is the start of the pulse, which is often steeper than therest of the
pulse, and is ended at the knee, the point of greatest change in slope;
-the pre-characteristic section. This is the section between the knee and theflattest section
of the pulse, its end being called the heel;
-the characteristic section. This is the flattest and often lowest frequency part of the pulse;
- the tail. This begins at the end of the characteristic section (characteristic point) and
runs to the end of the pulse. The tail may rise, drop or do both, they may vary within call
sequences, but the majority of pulses usually have tails typical of the species when in
search phase(Reinhold et al. 2001)(Fig 13).
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Figure 13: Features of a generic call pulse (Pennay et al., 2004)
There are four main categories of pulse shape namely; near vertical, flat, curved
and alternating (Corben and O‟Farrell 1999; Reinhold et al. 2001) (Fig 14).
Figure 14:Typical echolocation shapes of pulses, A Up-sweeping tail, B Tail absent, C Downsweeping tail, D Alternating, E Flat, F Flat, up-sweeping initial, G Near vertical (Pennay et al.,
2004)
I.4.3.3Call phases
Call sequence can be divided into three phases; Search phase, prey locating or
discriminating phase, and feeding buzz or terminal phase (Webster, 1963).Search phase
calls are produced to locate prey, approach phase calls are produced to identify exact
locations of prey, and terminal phase calls are produced just prior to capture. Search
phase calls are useful in the study of bat echolocation because they constitute a majority
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(90%) of calls produced by bats, exhibit consistency in structure throughout the call
sequence, and may possess species-specific characteristic(Betts, 1998, O‟Farrell et al.,
1999b) (Fig 15).
Figure 15: Phase transition in echolocating Bats(Ulanovsky, 2010)
I.4.3.4Acoustic features of bat echolocation signals.
Echolocation calls are characterized by variations in frequency and temporal
features of calls. This variations produce echolocation calls suited for different
environments and hunting behaviors (Simmons and Stein, 1980; Zupanc, 2004; Fenton,
2005; Jones and Teeling, 2006).
 Frequency of bat echolocation signals
The frequencies used in echolocation by bats fall usually between 25 kHz and 100
kHz, although some species emit and analyze principal components as high as 150 kHz
(Grinnell,1995). They can be composed of two different types of frequency structures:
Narrowband and Broadband Frequency signals. Narrowband components comprise two
subtypes: quasi-constant frequency (QCF) elements with frequency changes of a few kHz
(shallow modulation), and long constant frequency (CF) elements with frequency
changes of a few hundred Hz. Broadband components consist of a downward frequencymodulated (FM) element of large bandwidth (steep modulation)(Schnitzler and kalko,
2001).
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Bat echolocation calls possess flexible combinations of constant and frequencymodulated component (Suga, 1992; Kalko and Schnitzler, 1993; Kanwal et al.,
1994).This enables them to meet up with the varied perceptual demands associated with
different echolocation tasks (Simmons and Stein, 1980; Neuweiler, 2000). Broadband
frequency-modulated sounds (FM sweeps) appear to be utilized by all echolocating bats
for target range discrimination. Whereas comparatively long, constant-frequency (CF)
sounds can be used for prey detection and identification (Simmons, 1973; Simmons and
Stein, 1980; Neuweiler, 2000; Schnitzler and Kalko, 2001). Bats can be grouped into
different sonor groups based on the type of signals they emitted;
 F M bats
Most insectivorous bat families use short, downward frequency-modulated (FM)
sounds that rapidly sweep across a wide range of frequencies (so it is a broadband signal).
FM bats forage in the open or at the edge of forests, using shorter, broadband signals
(Kalko and Schnitzler, 1998) that are well suited for target localization (Simmons, 1973)
and for separating figures and ground.
 CF/FM bats
There are two types of constant frequency (CF/FM) bats; long CF/FM and short
CF/FM bats. In the long CF/FM bats, signals have a long constant-frequency component
preceding an FM sweep (Grinnell, 1995) (Fig 16). Long CF/FM bats are very specialized
for detailed analysis of sounds in the range of the emitted CF. A large fraction of the
inner ear and most of the neurons is auditory neural centers are devoted to analysis of a
narrow range of frequencies around the CF. This neural configuration has been termed an
“acoustic fovea” (Schuller and Pollak, 1979; Grinnell, 1995). These bats control the
frequency of the emitted signal to compensate for Doppler shifts of returning echoes so
that the echo CF stays within the acoustic fovea (Fenton, 1995; Grinnell, 1995). Long
CF/FM bats usually hunt in cluttered environments where prey detection is harder for
bats that use only FM signals. In the Short CF/FM bats, pulses containing a short CF
component, terminating in a FM sweep (Grinnell, 1995). They use Doppler shift
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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information to some degree, but are less specialized for the CF frequency band analysis
than long CF/FM bats. It is also common for bats to modify the pulse structure according
to the environment. Some species emit pure FM signals when close to vegetation, but in
uncluttered environments prolong the pulse and reduce the amount of sweep to be able to
detect faint echoes from remote targets.
 Click bats
Some megachiropterans bats belonging to the genus of Rousettus and Eonycteris
can echolocate (Speakman, 2001) (Fig 16). Generally, bats of genus Rousettus emit
ultrasonic sounds by clicking their tongue (Möhres and Kulzer, 1956), whilst bats of the
genus Eonycteris echolocate by clapping their wings (Gould, 1988). In most species of
Rousettus, the echolocation clicks are emitted as double clicks which consists of two subclicks separated by a silent interval. Usually these sub-clicks are not distinguishable to
human unaided ear, but are heard as only one click. These bats use echolocation to find
their way around caves where they roost (Altringham, 1996).
Figure 16: Types of Bat Echolocation calls and example of Bats that produce
themUlanovsky (2010).
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 Intensity of echolocation calls
Intensities of the echolocation calls vary greatly from species to species. Measured
from 10 cm in front of the bat, the sound pressure levels vary from less than 60 dB to 120
dB (Griffin, 1958; Altringham,1996), with many species producing calls of intermediate
strengths. The environment and hunting behavior of the species influences call intensity.
Bats searching for airborne targets usually produce intense echolocation calls while those
searching for prey on surfaces (gleaners) depend more on quieter calls. Some species
such as Myotis emarginatus, are known to adjust their call intensity depending on the
situation (Schumm et al., 1991).
 Call duration of echolocation calls
A single echolocation call can last from 0.2 to 100 milliseconds in duration,
depending on the stage of prey-catching behavior that the bat is engaged in. The duration
of a call usually decreases when the bat is in the final stages of prey capture. This enables
the bat to call more rapidly without overlap of call and echo. Reducing duration comes at
the cost of having less total sound available for reflecting off objects and being heard.
 Call interval of echolocation calls
Bats increase the repetition rate of their calls that is, decrease the pulse interval as
they home in on a target. This allows the bat to get new information regarding the target's
location at a faster rate when it needs it most. Secondly, the pulse interval determines the
maximum range that bats can detect objects. Bats are able to modify the echolocation
signal according to their needs. A good example of this is the terminal hunting phase in
which the short distance and the need for accurate locating abilities necessitate rapid
pulse sequences. Several FM bats modify the pulse form according to environment, so
that while gleaning, they use short broadband pulses of medium intensity, while in open
spaces the FM modulation is weaker and pulse duration longer and intensity higher
(Fenton, 1995). Tests performed by (Wadsworth and Moss, 2000) indicate that the FM
bat Eptesicus fuscus is able to actively modify the call signal according to the given task
so that in echo delay tasks mainly short broadband signals were used and in Doppler
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discrimination tasks long and relatively shallow signals were used. It is also well known
that CF/FM bats are able to adjust their signal frequency so that the Doppler-shifted
signal frequency falls within the frequency range of their „acoustic fovea‟ (Fenton, 1995).
I.4.3.5 Production time of echolocation calls
The timing of production of echolocation calls separates bats using laryngeal
echolocation into two categories: those signaling at high duty cycles and those signaling
at low duty cycles (Fenton, 1999). The duty cycle of a periodic sound is defined as the
proportion of time spent emitting signals in a given period;
 Low duty cycle bats
These bats have a duty cycle of less than 20% they are unable to process echoes
overlapping with the pulse. In this system, the emitted pulses and returning echoes are
separated in time (Fenton, 1995; Fenton et al., 1995). The bats use a wide variety of
echolocation type signals, most of which include FM (Frequency modulated)
components. Search phase call sequences are characterized by short signal pulses with
relatively long gaps between them (Fenton, 1994; Schnitzler and Kalko, 1998).The
majority of extant insectivorous bats use this system including all FM and short CF/FM
bats.
 High duty cycle bats
These are bats, which have a duty cycle that regularly exceed 80%, and they can
tolerate overlap between pulses and their echoes. In this system, the pulse and echo are
separated in frequency rather than time (Fenton et al., 1995). The bats produce long CF
echo signals that overlap with returning echoes. They utilize the Doppler shift effect,
which shift the frequency of returning echoes to a lower frequency than that of the
original pulses (Fenton et al., 1995; Neuweiler, 1990; Schnitzler and Kalko, 1998).These
bats avoid self-deafening by separating pulse and echo in frequency. Species in the
families‟ Hipposideridae, Rhinolophidae and Mormoopidae use high duty echolocation
calls (Fenton, 1995).
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I.4.4 Production and emission of echolocation Signals
Insectivorous sonar calls are generated in the larynx (Altringham, 1996). The larynx also
controls the frequency patterns, temporal sequences, durations of emitted sounds
(Cynthia et al., 2001). Their larynx is proportionally larger than in most other mammals,
but the mechanism of action is the same. Many insectivorous bat species possess vocal
membranes, which are thin upward extensions of the membranous portion of the vocal
folds (Mergell et al., 1999) (Fig 17). These membranes have been suggested to act as
independent low-mass oscillators and thus support generation of ultrasonic sonar calls
(Griffin, 1958). Vocal membranes are also thought to increase vocal efficiency (SchonYbarra, 1995). In their modeling, experiments Mergell et al., 1999 concluded that both
theories are correct; vocal membranes both allow bats to produce higher-pitched sounds,
but also to produce a given sound louder and more efficiently.
Figure 17:Schematic illustration of the anatomy of the vocal membrane of an
echolocating bat (Mergell et al., 1999)
Sound produced by bats is emitted through the mouth or the nostrils. Nostril emissions
have advantage when foraging, because a bat can fly and echolocate with the prey in
mouth. Bats using the nostrils often have complex noseleaves composed of fold of skin
and cartilage. The noseleaves have varying complexity and shape. Noseleaves acts as
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acoustic lens, focusing the sound into a narrow beam, which cause increasing of
directionality of emitted calls and enhanced echolocation performance.
I.4.4.1 Auditory adaptation to perception of echolocation Signals
The auditory system of bats is adapted to special tasks of the spatial orientation
using sound to perceive the environment. It is built and operates in the similar manner as
in other mammals, although several adaptations are present (Neuweiler, 2000). Bat ear
anatomy resembles the ears of other mammals in form and function, although several
special adaptations are present and common in different species;
 Middle ear
Sound waves captured by the pinna of outer ear are transmitted to the inner ear. The
middle ear of microchiropteran bats is similar in structure to other mammals, although
small differences are present (Hill and Smith, 1984). The tympanic membrane (eardrum)
is relatively thinner than that of other mammals with comparable membrane areas (Hill
and Smith, 1984). The area of the tympanic membrane does not correlate with the body
size, but bats that operate with high frequencies generally have smaller eardrums than
bats that operate at lower frequencies. Sound that was perceived by pinna passes to
middle ear and causes vibration of eardrum (Hill and Smith, 1984). The vibrations are
passed to the oval window along three ears ossicles: malleus, incus and stapes. Those
media acts as filters, because of the vibration capabilities. The higher the frequency bats
produce and perceive the thinner the eardrum is and smaller and lighter middle ear
ossicles, because they vibrate more rapidly (Neuweiler, 2000). Vibrations of the oval
window are transmitted along the spiral canal of the cochlea.There exist two muscles in
the middle ear; the tensor tympani (attached to the malleus and serving to tighten the
tympanum) and the stapedius (attached to the stapes and serving to pull the stapes away
from the oval window) (Hill and Smith, 1984). The stapedius is very important; FM bats
use it to control the signal amplitude entering the cochlea by contracting it before pulse
emission and gradually loosing it after the emission (Hill and Smith, 1984). In the final
stages of taking an insect, the stapedius muscle may operate at a frequency of more than
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200Hz one of the highest rates recorded in vertebrate muscle (Neuweiler, 2000).
Furthermore, the stapedius muscle acts as an automatic gain control for the signal
entering the cochlea (Hill and Smith, 1984). Contraction of the stapedius muscle strongly
attenuates sensitivity to the emitted signal, weakly attenuates response to echoes from
nearby targets, and leaves the auditory systems maximally sensitive to echoes from
distant objects (Grinnell, 1995). Because the echo energy falls sharply with distance, the
cumulative result of these phenomena is a form of an automatic gain control in bat
hearing, so that the level of the echolocation signal entering the cochlea stays
approximately equal.
 Cochlea
The cochlea of insectivorous bats is specialized for the use of high frequencies and, in
CF/FM bats, for hyper acuity around the CF (Grinnell, 1995). The inner canal of the
cochlea is a tube, scala media, filled with fluid. A second tube, whose upper part is called
scala vestibuli and the lower part scala tympani, covers it. Both of those tubes are
separated from middle ear by membranes of the oval and round windows. The floor of
the scala media is formed by the basilar membrane with sensory hair cells. The basilar
membrane of microchiropteran bats is narrower and thicker than in most nonecholocating mammals, which reflects adaptation to high-frequency sensitivity (Kossl
and Vater, 1995). Each hair cell on the basilar membrane posses‟ bundle of stereocilia.
The tectorial membrane covers the sterocilia tips. Vibration of the basilar membrane
against the tectorial membrane causes shearing of the hair cell sterocilia and
consequently, oscillations in the receptor potential that follow the rhythm of basilar
membrane movement. The oscillation progresses along the length of the basilar
membrane, decreasing its speed. When the stimulus is a high frequency sound, the
travelling wave moves only a short distance along the basilar membrane. The lower the
frequency, the farther the traveling wave moves within the cochlea. Thus, high
frequencies activate only the most basal hair cells, and lower frequencies activate the
apical hair cells most strongly (Neuweiler, 2000).Each hair cell is activated by specific
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frequency, its „best frequency‟. The frequency map of the basilar membrane varied
between CF and FM bats. The CF bats have „personal‟ constant frequency, which show
small variation in a resting specimen (Schnitzler, 1968). Therefore, there is a mechanical
filter in cochlea tuned to very narrow frequency band of about several kHz. The cochlea
of CF bats has the expanded representation of a narrow frequency band of only 6 kHz
around the individual‟s pure-tone echo frequency. This very narrow filter in CF bats is
called „auditory fovea‟. The auditory fovea of each individual bat is precisely tuned to its
own emitted frequency (Vater et al., 1985). The central auditory system of bats consists
of the same nuclei as in other mammals; however, some of these nuclei are relatively
larger than they are in other mammals. The impulses from the hair cells in the inner ear
are transfer to the auditory nerve fibers, which further transmit the impulse to the
midbrain auditory centre, called inferior colliculus. In echolocating bats, the inferior
colliculus is large. It gathers all pathways together and transmits information to the
medial geniculate body of the thalamus. From thalamus, the information proceeds to the
auditory cortex in forebrain where the final processing of the sound happened and sound
is translated into images of the environment (Neuweiler, 2000) (fig 18).
Figure 18: The schematic plan of the mammalian ear and sound wave flow from the pinna to the
inner ear (Neuweiler, 2000).
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CHAPTER II: MATERIAL AND METHODS
II.1 Description of study area
II.1.1 Presentation of the town of Maroua
The study was conducted in Maroua; capital of the Far- North Region of
Cameroon. The Far-North region is situated in the Sudano-sahelian zone of the country.
This region is situated between latitudes 10o and 13o North and between longitudes 13o
and 15o East (Yengue and Yann, 2002). It is bounded to the north and east by the republic
of Tchad, to the west by the republic of Nigeria and to the south by the North Region of
Cameroon.
II.1.1.1 Relief
The town of Maroua is situated in a vast plain surrounded by mountains (mount
Mandara). To the south, we have the Makabay highland and to the north we have the
Maroua highland. The mountain has an altitude of about 1000m while the plain has an
altitude of about 300m (Yengue and Yann, 2002).
II.1.1.2 Climate
The Far-North region has the sudano-sahelian (semi-arid) climate characterized by
variations in climatic elements (Boutrais, 1984).There are two alternating seasons; a long
dry season that runs from October to May and a short rainy season from June to
September. About 70% of the total annual rainfall, which stands at about 600-900 mm is
usually recorded in the months of July and August. The average temperature is about
28oC but can attain a maximum of 45oC in the months of March and April, and a
minimum of 18oC in December and January (Yengue and Yann, 2002). The vegetation of
the Far-North Region is characterized by very few and scanty trees and shrubs in the
environment (MINADER, 2003). This vegetation grows on soils of sandy and rocky
nature (Boutrais, 1984).
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II.1.1.3 Hydrography
There are two main rivers that flow through the town of Maroua; we have river
Tsanaga at the southern entrance of the town and river Kaliao at the center of the town.
These rivers have water that flow on the surface during the rainy season (May to
September) and no surface water during the dry season (October to April). The riverbeds
are dry during the dry season because water percolates into the sandy riverbeds. Several
bridges have been constructed on these rivers to facilitate communication. This
includes"Pont palar" and "Pont Makabay" at the entrance of the town and "Pont rouge",
"Pont jaune" and "Pont vert " at the center of the town. These bridges provide drinking
water for bats in the dry season as they usually harbor boreholes dug by humans to get
water into the sand. They also provide perfect roosting site for several species of bats.
II.1.1.4 Inhabitants
Maroua is a cosmopolitan town. It is made up of many ethnic groups among which
are the Guiziga, Toupouri, Foulbe, Moundang, Mousgoum and Moufou who constitute
the indigenous population, as well as Cameroonian from other part of the country and
even foreigners. The two main religions are Islam and Christianity. The population is
very dynamic and is involved in diverse activities such as agriculture, animal husbandry,
commerce and artistry. Crops like corn, millet, groundnut and cotton are grown while
animals like cattle, sheep, pigs and goats are reared for commercial and subsistence
purposes (Seignobos and Iyebi, 2000).
II.2 Capture sites
We targeted three maintypes of sites for capture and acoustic registration. We
have roost site, foraging site and drinking sites.
II.2.1 Roost sites
There were two type of roost site, crevices of some buildings and the underside of
bridges."Pont Palar" is a bridge constructed on one of the tributaries of river Kiliao while
"Pont Makabay" is constructed on river Tsanaga and is situated on the on the southern
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entrance of the town. Colonies of bats have made their niche on the crevices found on the
underside of both bridges.
II.2.2 Foraging and drinking sites
We also captured bats on site where bats are known to forage such as farmlands
and under trees. The farmland contained young corn and okra crops. The drinking sites
were all located on the different riverbeds.
The geographical position of the different capture site was taken using a portable
GPS (Etrex) receptor. The coordinates are presented in the table 1.
Table 1: Geographical coordinates of capture and acoustic monitoring sites and the
number of sessions.
Capture sites
Habitat
Pont rouge
Mizao
Mizao I
Pont Polar
Pont Makabay
Pont vert
College de l‟espoir
Pont jaune
Drinking site
Drinking site
Farmland
Roost site
Roost site
Drinking site
Roost site
Drinking site
Numberof
capture
session
4
3
1
1
1
4
1
3
Altitude North
402 m
403 m
403 m
414 m
420 m
404 m
401 m
403 m
10°35‟47,7‟‟
10°35‟58,8‟‟
10°35‟90,2‟‟
10°35‟37,2‟‟
10°34‟24,5‟‟
10°35‟38,5‟‟
10°35‟39,8‟‟
10°35‟90,2‟‟
Masters II Dissertation, University of Maroua (E.N.S)
East
14°18‟54,1‟‟
14°18‟44,4‟‟
14°20‟25,0‟‟
14°17‟19,5‟‟
14°16‟54,6‟‟
14°20‟15,2‟‟
14°17‟18,5‟‟
14°20‟25,0‟‟
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II.3 Methods of data collection and analyses
II.3.1 Capture of Bats
Free-flying bats were captured using a mist nets with four pockets (9 x 2.60 m
(mesh of 16 mm) that was tied between four-meter long wooden pools. The mist net was
positioned across known flight paths such as; foraging sites, over water bodies or outside
roosts. It was deployed from dusk up to about midnight. It was often checked with a flash
light. Each time an individual was caught, the bat was carefully untied by an observer
before been placed individually in a cloth-holding bag with a drawstring closure for
transportation to the laboratory for species identification.
II.3.2 Identification of bats
Identification was done the following morning after capture. Bat species were
identified using external characteristics. All individuals were measured (lengths of
forearm, head and body, tail and pinna) using a vernier calipers to 0.02 mm. The sex of
each bat was recorded and juveniles distinguished from adults by the presence of
cartilaginous epiphyseal plates in the finger bones (Anthony, 1988). These biological
parameters were used to identify the species of bats using two identification manuals,
Rosevear, (1965) and Hayman and Hill, (1971). The identification also took into account
data from African Chiropteran Report 2011. After proper identification, individuals were
now release for validation of echolocation calls.
II.3.3 Anabat acoustic recording
Bats echolocation calls were recorded in flight after hand-released. The recording
was done by an observer who stood about 20 meters infront of the point of release. He
immediately switched on the detector as soon as the bat took off from the hands of an
observer. At times the person who held the Anabat detector followed bats for some
distance on foot. The sensitivity of the detector was adjusted to three.
All recordings were done using the Anabat SD 1bat detector (Titley Electronics). The
Anabat Detection System consisted of a bat detector and CF (compact flash) storage
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ZCAIM (Zero-Crossings Analysis Interface Module). Call files were recorded to the
compact flash card contained within the CF storage ZCAIM. Call files were downloaded
from the CF card using the CFCread ZCAIM interface software and stored in special
folder. The CF card was erased each time a fresh recording was made. Call files were
labeled with date and locality information before been stored in the hard drive of a
computer.
Figure 20: Anabat SD 1 Bat Detector Maroua, 2013
II.3.4 Statistical analysis of data
II.5.1.1 Calculation of sampling or capture effort
One net hour = One capture net per hour.
One net night = One capture net for 12 hours.
The capture effort was calculated for the equivalent of 9 m of net for each capture site
using the formula;
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The data was stored in Microsoft excel and later treated with software ESTIMATES
9.0.0. Based on the number of species captured at the different sites, the index of
diversity alpha and beta were calculated in other to estimate the number of species
potentially present at the different sites.
 Diversity alpha gave ACE (mean), Bootstrap (mean) and the Chao 1 (mean).
-The real species richness was then estimated by using the following formula;
-The species accumulation curve was generated according to the number of
observed species (Sobs means).
-The sampling efficiency was calculated using the formula;
 Diversity beta gave the complementary indices of Jaccard Classic and Sorensen
Classic. This was used to compare sampling at the different capture sites.
II.5 1.2 Analyses of echolocation calls
To ensure the most accurate possible description was obtained, only the best
echolocation call was chosen from the call sequence or call files fromeach individual bat
for analysis (Barclay et al.,1999). The choice was based on call quality (kofoky et al.,
2009). We selected one of the last echolocation calls in each sequence, with a high signal
to noise ratio (Jennings et al., 2004) considered a search phase call (Betts, 1998).Calls
were filtered before measurement using filter command in Analook designed to exclude
echoes, unwanted noise. Additional cleaning was done using the off dot in Analook.
Sequence files chosen for further analysis were those that contained atleast five pulses.
This was to ensure that selected variables could be measured with confidence.
Calls were analysed using Analook software (Chris Corben, version 4.8).We
measured values of 10 parameters form each chosen call using Analook software
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(Table.2). Analook automatically calculate these parameters from each pulse and then
averages over the entire call.
Table 2: Description of the 10 call parameters calculated by Analook software from each
call.
Call parameters
S1
Sc
Fmax
Fmin
Fmean
Description
Units
Ops
Octaves per second(ops)
kHz
kHz
kHz
Fk
Initial slope of call
Slope of the flattest section of the call
Maximum frequency of the call
Minimum frequency of the call
Mean frequency of the call
(weighted by time spent at each frequency)
Frequency at the Knee ( Point of inflection)
Fc
Dur
Tk
Tc
Characteristic frequency
Duration of the call
Time into the call when Fk is reached
Time into the call when Fc is reached
Kilohertz (kHz)
milliseconds(ms)
ms
ms
kHz
II.5 1.2.1 Qualitative analysis of echolocation calls
Sonogram of call file sequences were examined and classified into three main
categories as defined by Schnitzler and Kalko, (2001). This includes:
- frequency modulation, followed by constant frequency, ending in frequency modulation
types(FM/CF/FM);
-frequency modulation types (FM);
-frequency modulation followed by Quasiconstant frequency types (FM/QCF).
A representative sonogram for each species was presented after description.
-student t-test was used to test for significance between the mean frequency and call
duration of some species.
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II.5 1.2.2 Quantative analysisof echolocation calls
To test the validity of assigning echolocation calls to species groups, a
discriminate function analysis (DFA) was performed using SPSS version 17.0.
-the analysis determines which variables discriminate between species using discriminant
functions (Digby and Kempton, 1987).
-canonical analysis produces eigenvalues, which indicate the strength of the functions in
differentiating one group from another.
-Wilk‟s lambda is used to test the significance of all the discriminating functions in
separating groups of data. The significance level of lambda is determined from the
distribution of Chi-square.
-to obtain a graphical representation of the separation of groups based on their
discriminant functions, we plotted the group centroids with 95% confidence limits for
separate functions and the canonical discriminant functions.
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CHAPTER III: RESULTS AND DISCUSSION
Eight sites were sampled within the Maroua area. Mist-net were monitored for 108
net hours and resulted in 96captures of 13species and representing seven genera in three
families (Vespertilionidae, Molossidae, and Rhinolophidae).
Table 3: Number of individuals captured per site, Capture effort and Capture success. Site
1 :Pont verte : Site 2 :Pont rouge :Site 3 :Pont jaune :Site 4 :Pont Makabay :Site 5 :collège
del‟espoir ;Site 6 :Mizao 1 :Site7 ; Mizao : site 8 : Pont palar.
Species
Sites
S1
Chaerephon major
Chaerephon nigri*
Chaerephon pumilus
Mops condylurus
Mops niveiventer
01
-
Nycticeinops
schilieffenii
Pipistrellus nanus*
Pipistrellus nanulus
Pipistrellus inexpectatus
Scotoecus hirundo
Scotophilus dinganii
Scotophilus leucogaster
-
Rhinolophus fumigatus*
16
03
62.4
0.25
Total
Total species
Capture effort
Capture success
05
10
Number of individuals captured per site
S2
S3
S 4 S5
S6
S7
S8
Molossidae
22
01
01
02
01
02
01
11
10
Vespertilionidae
01
-
total
23
01
06
12
10
01
01
12
03
01
01
01
01
01
01
01
02
03
05
20
03
01
17
Rhinolophidae
01
01
20
30
23
0
02
09
0
96
06
06
04
0
01
04
0
13
62.4 46.8 15.6 0
15.6 46.4 0
249.2
0.32 0.06 1.47 0
0.19 0.13 0
2.132
(* species captured for the first time in Maroua)
The predominant species were Chaerephon major (n=23), Scotophilus dinganii
(n=20) and, Scotophilus leucogaster (n=17), Mops condylurus (n=12), Mops niveiventer
(n=10). The capture of Chaerephon nigri (n=1), Rhinolophus fumigatus (n=1) and
Pipistrellus nanus (n=1) were the first documented individuals in the Maroua area.
(Table3). The capture of these species has brought the total number of documented
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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microchiropteran species in the Maroua area to 18. This capture also brought to light the
need of additional studies and the necessity of more complete inventories. Inventories
done not only with the traditional capture techniques but also with the use of acoustic
techniques which often determine presence of more species at a site than capture
techniques (Kuenzi and Morrison, 1998). No species were captured in site 5(college de l‟
espoir) and site 8(Pont palar). The reason being that in site 5, the colony had migrated
because of human disturbance due to renovation work. No individuals were captured in
site 8 because of the disturbance by rain. Precipitation can influence bats activity and
survival by wetting the bat‟s fur and reducing it insolating value (Tuttle and Stevenson,
1982) and by interfering with their ability to echolocate (Griffin 1971; Grindal., 1992).
Precipitation also deter insect from flying, making them unavailable to most bat
(Anthony et al., 1981).
III.1 Estimating species Richness
III.1.1Diversity ALPHA
`
The specific indices ACE (mean), Bootstrap (mean) and Chao 1 (mean) was used
to estimate the species richness of insectivorous bats in Maroua to be 34.18, 14.78, and
21.63 respectively. The average of these three estimations enabled us to calculate the real
species richness to be 23.53. This species richness is slightly higher than 22.04 species
calculated by Bol et al., (2011). This can be attributed to the fact that there were fewer
capture sites and fewer individuals captured.. This then permitted us to also calculated
sampling efficiency, which was 84.3%.
A sketch of species accumulation curve using the number of observed species (sobs
mean) is illustrated in the figure 21 below.
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20
18
16
Number of species
14
12
10
8
6
4
2
0
0
12,63
25,25
37,88
50,5
63,13
75,75
88,38
96
Number of individuals
Sobs Mean (runs)
Sobs 95% CI Lower Bound
Sobs 95% CI Upper Bound
Figure 21: Accumulation curve of insectivorous bat species sampled in the town of
Maroua
The species accumulation curve of insectivorous bats in the town of Maroua rises steadily
without attaining an asymptote (Fig 21).This shows that the sampling of insectivorous
bats was incomplete and there is still a possibility of adding new species to the inventory.
This interpretation is confirmed by calculations of the efficiency of sampling which
stands at 83.4%.Thus, not all species of insectivorous bats in Maroua were captured and
their echolocation calls recorded. This is further confirmed by calculation of the real
specific richness present in the Maroua of 23.53 species. The difference between the
number of species of insectivorous bats actually captured and the number of species
potentially present may be due to the lack of complementary sampling techniques such as
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the use of harp traps and ultrasonic detectors and the period of capture, which was
relatively limited and did not cover the entire year.
This variation in the species accumulation curve is similar to the accumulation curve of
Bol et al., (2011) during their inventory on the chiroptera fauna in the town of Maroua.
This suggests that it is not possible to actually obtain the real specific richness when
sampling is limited. Chao et al., (2005) showed that it is practically impossible to detect
all species present in an ecosystem and their abundance when the number and intensity of
sampling is limited. To ensure more complete inventories, a combination of standard
capture methods and acoustic detection are required (Micheal O‟farrel and William L.
gannon, 1999).
III.1.2 Diversity BETA
The bata diversity shows the distribution of species between the capture sites. This
was calculated using the complementary indices of Jaccard Classic and Sorensen Classic as
illustrated in Table 4.
Table 4: Comparison of two complementary indices of Jaccard Classic (red) andSorensen
Classic (Blue).Site 1 :Pont verte ; Site 2 :Pont rouge : Site 3 :Pont jaune ; Site 4 :Point
Makabay :, Site 5 :collège de l‟espoir :Site 6 :Mizao 1 ;Site7 :Mizao ; site 8 : Pont palar .
Sites
1
2
3
4
5
6
7
8
1
1
0.50
0.43
0.33
0
0
0.33
0
2
0.67
1
0.37
0.13
0
0
0.29
0
3
0.60
0.34
1
0.25
0
0
0.43
0
4
0.50
0.13
0.40
1
0
0
0
0
5
0
0
0
0
1
0
0,
0
6
0
0
0
0
0
1
0
0
7
0.50
0.29
0.60
0
0
0
1
0
8
0
0
0
0
0
0
0
1
1= two capture sites that have every thing in common.
0= two capture sites that have nothing in common.
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The sampling sites were compared to each other using the complementary indices
of Jaccard Classic and Sorensen Classic. Table 4 shows that some sites are very similar to
each other while others have nothing in common in terms of species specificity. Sorensen
classic = 0.67 and Jaccard Classic =0.50shows that Pont vert and Pont rouge are the two
sites that show the highest similarity in term of number of species present. This means
that the two sites have at least 50% of species in common. These sites are complementary
to each other and greatly contribute to diversity of insectivorous bats in Maroua. These
drinking sites are physically very similar as they contain water throughout the year. The
similarity may also be attributed to the fact that both sites had the same sampling effort of
62.4 net hours. When the sites at Pont jaune and Mizao were compared , it was observed
that they do not have exactly the same species even though they are very close to each
other (Jaccard Classic = 0.43, Sorensen classic = 0.60 ) and have almost the same
sampling effort of 46.8 and 46.4 respectively. This difference can be attributed to the fact
that bats are often faithful to their drinking and foraging site (Allen, 1952; Grassé,
1955).The result also reveals that some site have nothing in common either because very
few or no animals were captured at those sites. Generally, variation in the number of
species present at the different sites can be attributed to factors such as the difference in
sampling effort among sites and the fact that most animals shall prefer to forage or drink
near their roost where they shall spend very little energy while maximizing their energy
gain.
III.2 Qualitative analysis of echolocation calls
III.2.1Characterisation of echolocation signals
The shape of the search phase call exhibit consistency in structure throughout the
call sequence, and possess species-specific characteristics. They are thus useful in the
study of bats (O‟Farrell et al., 1999b).Qualitative identification involves an observer
determining the identity of a species based on the features of a bat‟s calls, after viewing a
sonogram (Betts, 1998). The Analook software, displays bat calls graphically in a
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frequency (kHz) by time (seconds) sonogram. The best sonograms of the different
species are shown below.
Family Molossidae
Five species belonging to this family were captured during our study. This include
Chaerephon major (Troussart, 1897), Chaerephon nigri (Hatt, 1928) and Chaerephon
pumilus (Cretzchmar, 1830), Mops condylurus (A. smith, 1833)andMops
niveiventer(Cabrera and Ruxton, 1926).
Chaerephon major (Large free-tail bat)
This species is characterized by dark wings, white central area to the chest and belly, a
white band of hair on the underside of the wings between the upper arm and the tight and
a truncated- triangular lappet of skin that connect both ears. A total of 20 males and three
females were captured in January, 22 were captured in site 3(Pont jaune) and one in site 4
(Pont Makabay) in July.
Echolocation calls were recorded from all individuals in flight after hand release
and manual identification. Figure 22 shows a single call from the same bat.
-characteristic frequency between26.2 and 49.0 kHz (n=16);
The echolocation call is a frequency modulation (FM) call, which is characterized by
steep, linear pulses of highly variable frequencies and a slight leftward leaning. The
echolocation call shows frequency alteration with the initial pulses having lower
frequencies. The frequency then steadily rises and then drops again at the end of the call.
Fmean=41.8 kHz and characteristic frequency is 39.8.kHz.
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Figure 22: Sonogram of Chaerephon major in flight after hand release (F7, compressed)
Chaerephon nigri(Niger free-tail bat) has become Chaerephon pumilus
This species lacks the band of white fur present on the underside of the wing of
other Chaerephons. Only one male individual was capture at the drinking in site 2(Pont
rouge) in the month of January.
-characteristic frequency Fc= 39.5 kHz (n= 1).
-echolocation sequence recorded from this individual shows the pulses to be made up of
broadband, steep, near vertical frequency modulation (FM ) calls with Dur=1.85ms.
The sonogram is of poor quality and the Anabat detector recorded very few files. This is
because some species produced very low intensity or high frequency signals that
attenuate rapidly (Faure et al., 1990) and are only detectable at a distance of a few
meters. This might also be because the sensitivity of the detector was not properly
adjusted to detect emitted signal.
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Figure 23: Sonogram of Chaerephon nigri in flight after hand release (F7, compressed)
Chaerephon pumilus(Cretzschmar’s Free-tail bat)
This species is characterized by blackish brown fur on the back. The fur is a
little paler on the abdomen. They possess pure white band of fur between the upper arm
and the thigh. Six individuals were captured in four different sites.One male and one
female were captured in site 2 (Pont rouge), two males were captured in site 7 (Mizao)
and a one male was captured in each in site site1 (Pont vert) and site3 (Pont jaune). All
captures were done in January.
Echolocation calls were recorded from each individual on hand release. Figure
24 shows a call sequence produced by the same bat.
-characteristic frequency 36.5 and 41.23 kHz (n= 3).
The call is a broadband steep, near vertical frequency modulation (FM) call.
The pulses show an alternation between higher frequency pulses that overlap with lower
frequency pulses.Fmin=35.1 kHz, Fmax=48.9 kHz Fmean=42.4 kHz and the
characteristic frequency is 40.5 kHz.
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Figure 24: Sonogram of Chaerephon pumilus in flight after release from hand (F8,
compressed).
Mops condylurus (Angola Free-tail bat)
This species is characterized by a crown, which is not as dark as the back, little
or no white on the underside and a well-developed sagittal crest. Four female and seven
males were captured in July while leaving their roost at site 4 (Pont Makabay).One
female individual was also captured at site 2 (Pont rouge).
Echolocation calls were recorded on hand release forms all of them. Figure 25
shows a call sequence of the same bat.
-characteristic frequency was between 30.1 and 40.0 kHz (n= 12);
-the calls were made up mostly of broadband, steep, near vertical frequency modulation
(FM) calls. High frequency pulses overlap with low frequency pulses with the frequency
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dropping at a certain point to below 25 kHz. The pulses have Fmax=39.4 kHz,
Fmin=36.3 kHz, Fmean=38.0 kHz. The characteristic frequency is Fc=36.5 kHz.
Figure 25: Sonogram of Mops condylurusin flight after handrelease(F8, compressed).
Mops niveiventer(White-bellied free-tailed Bat)
This species have crowns that are darker than their back, underside usually white and the
skull with the sagittal crest low when present. Ten individuals were capture in site 4
(PontMakabay) in July including seven females and three males.
Echolocation call was recorded from all of them on hand release. Figure 26 shows a single
call from a single female individual.
-Characteristic frequency between 30.1 and 37.6 kHz (n= 10).
The echolocation calls are made up of broadband, steep, near vertical FM call. The
pulses show an Fc=33.81 kHz, Fmax=36.4 kHz, Fmean=35.1 kHz.
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Figure 26: Sonogram of Mops niveiventer recorded in flight after hand release (F7,
compressed).
Vespertilionidae
Seven species belonging to this family were captured during this study. These
includeNycticeinops schilieffeni (Peters, 1859) Pipistrellus nanus(Peters, 1852),
Pipistrellus nanulus (Thomas, 1904), Pipistrellus inexpectatus (Aellen, 1959), Scotoecus
hirundo (Winton, 1899), Scotophilus dinganii (Schreber, 1774), Scotophilus leucogaster
(Cretzchmar, 1826)
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Nycticeinops schilieffeni (schilieffeni’s bat)
This species is characterized by fur that is unicolor throughout it length,wings are
medium brown with darker venation and the presence of a fairly long single incisor on
each side of the upper jaw.A single male individual was captured in at site 3 (Pont jaune).
Echolocation signals recorded from it showed the sequence below.
-characteristic frequency Fc=41.4 kHz (n= 1).
-The signals are broadband, steep, vertical frequency modulation (FM) signals with,
Fmax=51.3 kHz, Fmean=40.0 kHz and Fmean=45.7 kHz (fig 27).
The spectrogram is of poor quality probably because the animal produced calls of very
low intensity that was not picked up by the detector. It might also be caused by the fact
that the sensitivity of the detector was not adjusted to pick up this signals.
Figure 27: Sonogram of Nycticeinopsschilieffeniiin flight after handrelease(F5,
compressed)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Pipistrellus nanus (Banana bat)
This species is characterized by two upper incisors on both sides of the jaw and a
tragus which is hatched shaped (outer margin with an abrupt angle). The fur is
bicoloured, blackish at the base with yellowish golden brown and deep reddish brown at
the tip.A single male individual was captured at site 6 (Mizao) in January. Echolocation
call were recorded on hand release. Figure 28 shows a call sequence from the same
individual.
-characteristic frequency Fc=96.6 kHz (n=1).
The echolocation call is FM/QCF call. The pulses are curved, with highly variable
frequencies. Each pulse start with an initial FM sweep that end with a QCF sweep. Very
high frequency pulse alternate with lower frequency pulses Fmax=106.4 kHz, Fmin=96.6
kHz and Fmean=101.6 kHz. The characteristic frequency is around 96.6 kHz.
Figure 28: Sonogram of Pipistrellus nanus in flight after hand release(F9, compressed)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Pipistrellus nanulus (Tiny Pipistrelle)
This species are characterized by fur which is unicolor at the back and a sickled
shaped tragus. One individual was captured at site 2 (Pont rouge).Echolocation sequence
of that individual is shown in figure 29.
-characteristic frequency Fc=45.8 kHz (n=1).
The call is an FM/QCF call, made up of curved frequency modulation (FM), quasiconstant frequency (QCF) pulses that end in a slight downward droop. Fmax=65.5 kHz,
Fmin=45.5 kHz and Fmean=51.3 kHz. The characteristic frequency of the call is around
45.8 kHz.
Figure 29: Sonogram of Pipistrellus nanulus release from hand (F9, compressed)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Pipistrellus inexpectatus (Aellen’s Pipistrelle)
This species are characterized by bicolor fur at the back, blackish brown at the
base and brilliant red brown in the terminal half. Below, the tip of the hair is silvery white
and a distinct white margin running from the tip of the tail to the third digit. A single
individual was captured in site 6 (Mizao 1).Echolocation signals were recorded from this
individual in flight after hand release. Figure 30 shows a single call produced by the bat.
Characteristic frequency Fc=47.7 kHz (n=1).
The echolocation calls were broadband, near vertical, steep frequency modulation
(FM) calls. The pulses are highly clustered together. There is an alternation between high
frequency pulses and low frequency pulses Fmax=54.7 kHz, Fmin=47.7 kHz and
Fmean=51.2 kHz.
Figure 30: Sonogram of Pipistrellus inexpectatus in flight after hand release (F7,
compressed)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Scotoecus hirundo (Swallow bat)
This species are characterized by short round tragus and dark brown wing and tail.
Two individuals one female and one male were captured in site 7(Mizao) and site 3(Pont
jaune) respectively.
Echolocation signals were recorded from the bat in flight after release from the hand.
Figure 31shows a single sequence recorded from the same bat.
-characteristic frequency was between 54.5 and 54.8 kHz 9(n= 2);
-The call is a broadband FM/QCF call. Pulses possess an initial steep FM sweep
that end with a shallow QCF sweep and a slight downward droop. Fmax=59.6 kHz,
Fmin=54.8 kHz, Fmean=57.2 kHz. The call has a characteristic frequency of around 54.8
kHz.
Figure 31: Sonogram of Scotoecus hirundo release from hand (F7, compressed)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Scotophilus dinganii (Schreber’s Brown Bat)
This species are characterized by an underside which is yellowish. Twenty
individual were captured during this study at different drinking spots. Five individuals
were captured in site1 (Pont vert), twelve in site 2(Pont rouge), three in site 3(Pont jaune)
and seven in site 7 (Mizao). Echolocation calls were recorded from all of them in flight
after release from hand. Figure 32shows echolocation call emitted by a single male
individual.
-characteristic frequency was between 46.8 and 69.5 KHz (n=19).
The echolocation pulses are broadband, curved FM/QCF calls with an initial steep FM
sweep that ends with a QCF. The sequence start with low frequency pulses. The
frequency increases above 90 KHz then decreases again.
Figure 32: Sonogram of Scotophilus dinganii in flight after hand release (F7, compressed)
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Scotophilus leucogaster (Cretzchmar’s Brown bat)
These bats are characterized by an underside, which is whitish. Seventeen individuals
where captured during this study including 13 males and 4 females. Ten were captured in
site 1(Pont vert), three in site2 (Pont rouge), three in site 3(Pont jaune) and one in site 4
(Pont Makabay).
Echolocation calls were recorded from all of them in flight after release from hand.
Figure 33shows echolocation sequence emitted by a single male individual.
-characteristic frequency was between 61.1 and 55.0 kHz (n= 12).
The call is FM/QCF call, which is made up of pulses that are broadband, curved with an
initial FM sweep that ends with a QCF sweep. The initial pulses have lower frequency
that increases to just below90kHz then decreases again. Fmax=65.5 kHz, Fmin=45.5 kHz
and Fmean=51.3 kHz.
Figure 33: Sonogram of Scotophilus leucogaster in flight after hand release (F8,
compressed).
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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Rhinolophidae
One speciesRhinolophus fumigatus (Rüppell 1842)was capture during our study.
Rhinolophus fumigatus (Abyssinian Horseshoe Bat)
This species are characterized by a bluntly ending sella connecting process, longish
fur that is sepia grey above and whitish below, dark brown wings and horseshoe nose
leaf. A single male individual was captured in site 7(Mizao).The echolocation sequence
recorded from this individual is shown in figure 34.
-characteristic frequency Fc=61.6 kHz.
-The call is a FM/CF/FM call. The pulses are characterized by an initial upsweep, a
constant frequency in the middle and a terminal down sweep Fmax=62.6 kHz, Fmin=61.6
kHz and Fmean=61.9 kHz.
Figure 34: Sonogram of Rhinolophus fumigatus in flight after hand release (F6, truetime)
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III.2.2 Descriptive statistics of echolocation call parameters
Family Molossidae
Sonograms from all Molossidae show that their echolocation calls are broadband
FM calls. This implies that many of them forage in the open or at the edge of forests,
using shorter duration, broadband signals that are well suited for three dimensional target
localization and for separating figure and ground. They can discriminate differences in
echo delay, the cue for target distance, of less than 60 microseconds (Simmons, 1973)
and they use this delay information to coordinate the timing of sonar vocalizations (Moss
and Surlykke,2001).
The sonogram of Chaerephon major revealed they use broadband calls with
average mean, minimum and maximum frequencies of36.4 kHz, 34.2 kHz and 39.3 kHz
respectively (n= 16; Table 6) and an average duration of 1.66ms. The duration of the
pulseswas the highest among all the Molossidae. The frequencies used by this bat species
for echolocation lie between 34.2 and 39.3 kHz.
Chaerephon pumilus revealed mean, minimum, maximum frequencies of 41.2
kHz, 38.2kHzand 44.2 kHz respectively. We also found that the average duration of these
calls was1.32 ms with a range of 0.85 and 2.73 ms (n=3; Table 6). The frequencies used
by this bat species for echolocation lie between 38.2and44.2 kHz. These parameters are
higher than parameters of Chaerephon pumilus recorded in Kenya by (Taylor et al.,
2005). The Kenya recordings revealed narrow-band calls with mean, minimum,
maximum and peak frequencies of 24, 29 and 26 kHz respectively and duration of about
11ms.This difference might be due to differences in recording and analysis techniques,
clutter, atmospheric attenuation and Doppler effects (Papadatou et al., 2008). In addition,
we used the Anabat detector while Taylor et al.,(2005) used a Pettersson D980 Time
Expansion bat detector.
The recordings of Mops condylurus had maximum frequency range at 33.9 to 41.6 and a
minimum range at 30.1 and 40.0 kHz respectively (n=12; Table 6).This was slightly
greater than that for Mops niveiventer at 32.2 and 40.8 and 29.9- 37.6 kHzrespectively
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(n=10; Table 6).The frequencies used by Mops condylurus for echolocation lie between
34.2 - 39.2 kHz and that for Mops niveiventer lie between 34.1- 37.1 kHz (Table 6).A
T-test failed to reveal reliable difference between the mean frequencies emitted by these
closely related species t (17) = 1.239, p=0.232, α= 0.05. This two species are closely
related and may be share the same roost. Species with similar morphology and/ or
ecology may show convergent evolution of their call features and may share similarities
in their echolocation calls (Papadatou et al., 2008). Figure 35 shows that among the
molossid bats included in this study, Chaerephon pumilus emit calls with the highest
frequency. Chaerephon major has the highest duration for the emission of echolocation
calls. A t- test revealed a significant difference between call duration of Chaerephon
major and Mops condylurus t(23)= 6.408, P=0.000, α=0.005.
Frequency(kHz)/Duration(ms)
Av. Frequency/Duration
50
45
40
35
30
25
20
15
10
5
0
44,2
39,3
39,2
38,2
34,2
37,7
34,2
34,1
Fmax
Fmin
Dur
1,66
C. major
1,32
C. pumilus
0,78
0,74
M. condylurus
M. niveiventer
Species
Figure 35: Average maximum, minimum frequencies and duration of Chaerephon major,
Chaerephon pumilus, Mops condylurus and Mops niveiventer
Family Vespertilionidae
Vespertilionid species revealed echolocation calls that are of FM and QCF types.
Nycticeinops schilieffeniiand Pipistrellus inexpectatus showed purely FM type calls.
Nycticeinops schilieffenii had frequency range of 40.0 and 51.3 kHz. This fell within the
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
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range recorded in Kenya by Taylor et al.,(2005).Pipistrellus inexpectatus had a much
higher range at47.7 and 54.7 kHz (Table 6).
Pipistrellus nanus and Pipistrellus nanulus showed calls that were FM /QCF type.The
single sequence of Pipistrellus nanus showed the highest frequency among all the
vespertilionid bats with a mean frequency of 101.7 kHz (Table 6).This suggests that these
bats can typically be encounted in cluttered habitat. High frequency calls are known to
provide more structural details about a target (Griffin, 1958) enabling the bat to acquire
more information about the prey in a shorter period, and are most effective in cluttered
environments habitat.Pipistrellus nanulus on it part showed the longest call duration of
2.89 ms(Table 6). The two callsof Scotoecus hirundo showed an average maximum and
minimum frequency of 58.4 and 54.5 kHz respectively. Scotophilus dinganii and
Scotophilus leucogaster are two closely related species whose echolocation call
sequences differ slightly. Scotophilus dinganii had a maximum and minimum frequency
range at 49.4 and 84.8 kHz and 46.5 and 69.5 kHz respectively (n=19; Table 6). The
frequency range of Scotophilus leucogaster is slightly lower and lies at48.5 and 64.1 kHz
and 46.1 and 56.5 kHz respectively (n=12; Table 6). The frequencies used by Scotophilus
dinganii for echolocation lie at 52.6 and 58.5 kHz and that for Scotophilus leucogaster lie
at 50.6 and 55.7 kHz (Table 6).
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Average frequency
60
58,5
Frequency (kHz)
58
55,7
56
54
52,7
52
50,7
50
Fmax
Fmin
Fc
48
46
Scotophilus
dinganii
Scotophilus
leucogaster
Species
Figure 36: Average maximum and minimum frequencies for Scotophilus dinganii and
Scotophilus leucogaster
Thus it can be observed that among species whose echolocation signal was analysed,
Scotophilus dinganii
which is relatively the largest bat among all of them emit
echolocation signal with the highest frequency while Mops condylurus is said to have the
lowest frequency. It can also be observed that between the two Scotophilus species
Scotophilus dinganii emit echolocation calls with much higher frequency (Fig 36).
Family Rhinolophidae
Rhinolophus fumigatus produce FM/CF/FM calls. This indicates that they typically
forage in dense foliage, and they can adjust the frequency of their sonar vocalizations to
compensate for Doppler shifts in returning echoes (Metzner, 2002).Doppler shift
compensation (DSC) serves to cancel a rise in echo frequency introduced by its own
flight velocity and isolates spectral modulations in echoes that come from fluttering
insect wings.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Table 5: Summary of echolocation frequency used by insectivorous bats in Maroua.
Species
n
Frequency of echolocation calls
Chaerephon major
16
34.2 kHz -39.3 kHz
Chaerephon pumilus
03
38.2 kHz -44.2 kHz
Mops condylurus
09
34.2 kHz -39.2 kHz
Mops niveiventer
10
34.1 kHz- 37.1kHz
Scotophilus leucogaster
12
50.6 - 55.7kHz
Scotophilus dinganii
19
52.6 - 58.5 kHz
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north Region of Cameroon
Table 6: Descriptive statistics for Echolocation parameters of 13 species of insectivorous bats in the far-north region of Cameroon.
The table shows mean ± standard deviation, minimum- maximum of the eight, time and frequency parameters except for Rhinolophus
fumigatus, Pipistrellus inexpectatus, Pipistrellus nanus, Pipistrellus nanulus, Nycticeinops schilieffenii and Chaerephon nigri for
which only single individuals were captured respectively.
Family/species
Call. str
n
Fmax
Fmin
Fmean
Fk
Fc
Duration
Tk
Tc
39.3±6.9
31.9-53.1
39.2
34.2±6.7
25.9-49.0
31.1
Molossidae
36.4±6.7
28.7-51.0
50.0
38.2±7.3
29.9-53.1
37.9
33.7±7.3
26.2-49.0
33.6
1.66±0.40
0.85-2.73
1.85
0.35±0.28
0.00-1.19
0.07
1.46±0.36
1.17-2.44
1.34
44.2±3.4
40.4- 47.0
39.2±6.9
33.9- 41.6
38.2±2.6
35.3- 40.4
34.2±6.7
30.1- 40.0
41.2±3.0
37.9- 43.7
36.4±6.7
32.0- 41.0
44.1±3.4
40.4 – 47.0
38.2±7.3
33.9- 41.5
39.1±2.4
36.5- 41.2
33.67±7.3
30.1- 40.0
1.32±0.11
1.26- 145
0.78±0.89
0.57-0 .88
1.11±0.07
1.04 – 1.12
0.75±0.75
0.57- 0.80
10
37.7±2.9
32.2- 40.8
34.1±2.6
29.9- 37.6
35.9±2.8
31.1 –39.3
37.6±2.7
32.1 – 40.8
34.1±2.6
30.1- 37.6
0.74±0.10
0.65- 0.95
0.03±0.04
0.00- 0.02
0.003±0.1
0
0.00- 0.03
0.00±0.01
0.00 - 0.02
FM
01
51.3
40.0
Vespertilionidae
45.7
51.3
41.0
0.91
0.00
0.91
Pipistrellus nanus
FM/QCF
01
106.4
96.6
101.7
106.4
96.6
0.42
0.00
0.42
Pipistrellus nanulus
FM/QCF
01
65.5
45.6
51.3
49.2
45.8
2.89
1.56
2.83
FM
01
54.7
47.7
51.2
54.7
47.7
0.46
0.00
0.46
Scotoecus hirundo
FM/QCF
02
Scotophilusdinganii
FM/QCF
19
Scotophilus leucogaster
FM/QCF
12
Rhinolophus fumigatus
FM/CF/FM
Chaerephon major
FM
16
Chaerephon nigri
FM
01
Chaerephon. pumilus
FM
03
Mops condylurus
FM
12
Mops niveiventer
FM
Nycticeinops schilieffenii
Pipistrellus inexpectatus
01
`
58.4
57.2-59.6
58.5±8.9
49.4-84.8
55.7±4.3
48.5-64.1
54.5
54.2-54.8
52.6±6.2
46.7- 69.5
50.6±3.0
46.1-56.3
62.6
61.6
56.6
58.2
55.9-57.2
57.2-59.2
55.6±7.5
58.5±8.9
48.1-77.0
49.4-84.0
53.2±3.6
55.7±4.3
47.3-59.3
48.5-64.1
Rhinolophidae
61.9
6I.7
Masters II Dissertation, University of Maroua (E.N.S)
54.7
54.5-54.8
52.7±6.2
46.8-69.5
50.7±3.0
46.1-55.0
0.87
0.82-0.91
0.88±0.92
0.73-1.02
0.81±0.23
0.44-1.00
61.6
0.57
0.00
0.00
0.03±0.06
0.00-0.02
0.00±0.01
0.00-0.03
0.00
0.71±0.65
0.65- 0.83
0.86
0.82-0.89
0.86±0.84
0.67-1.00
0.80±0.21
0.44-0.98
0.56
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
III .3 Quantitative analysis of echolocation signal
III.3.1Discriminant function analysis
The discriminant function analysis was performed using seven variables as
predictors of membership to five-bat pecies-group (grouping variable). The predictors
were Fmax, S1, Sc, Fmin, Fmean, Fc and Tk. The variables Dur, Tk and Tc failed the
tolerance test were not included in the analysis. Species in which single or very few
individuals were captured were not including in the DFA. This involved eight of the 13
captured species. Using the criterion 65 echolocation calls belong to the five species were
finally considered for the Discriminant function analysis.
The five bat species were Chaerephon major, Mops condylurus, Mops niveiventer,
Scotophilus leucogaster, and Scotophilus dinganii. These calls chosen were considered to
belong to search phase. Only calls containing more than five pulses were considered for
analysis.
 Test of equality of variance
Using an alpha level of 0.05 to evaluate the homogeneity of covariance assumption,
Box's M test was significant (F=5.781p = 0.000). Thus, reject the null hypothesis and
conclude that groups do not differ in their covariance matrix. This violates an assumption
of Discriminant analysis. However, discriminant function analysis is robust even when
the homogeneity of variances assumption is not met provided the sample is large and
there are no outliers (Table 7).
Table 7: Test of homogeneity of variance
Test Results
Box's M
F
915.371
Approx.
df1
df2
5.781
112
4206.447
Sig.
0.000
Tests null hypothesis of equal population covariance matrices.
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
 Summary of canonical Discriminant Function
Four Discriminant functions were produced. The first discriminant function
accounted for 58.2% of the total variation between bat species and the second 40.3%.
Only the first two functions were important because they accounted for 98.5%of the total
variation. The first function has canonical correlation of 0.916. This indicates that it
explains 83.9% of the grouping variable and the second function explains 78.3% (Table 8)
Table 8: Relative power of discriminant functions
Function
1
2
3
4
Eigen value
5.216
3.615
0.098
0.036
Eigen values
% of Variance
Cumulative
%
58.2
58.2
40.3
98.5
1.1
99.6
0.4
100.0
Canonical
Correlation
0.916
0.885
0.298
0.186
. First 4 canonical discriminant functions were used in the analysis.
 Wilks’ lambda
The Four canonical discriminant functions obtained for the species groups gave a
combined χ2 (28) = 205.604, p< 0.05. It indicated that the function as a whole is
significant and the discriminant function does better than chance at separating the bat
calls into groups. After removal of the first function, there was still a strong association
between bats pecies and predictors, χ2 (18) = 97.084, p<0.05. After removal of the second
function, χ2 (10) = 7.572, p=0.671 there was no longer a strong association between bat
species and predictors. The first function (Wilks' Lambda =0.31) has the greatest
discriminatory ability in classifying calls in different groups(Table 9).
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Table 9:Wilks‟ lambda table
Test of
Function(s)
1 through 4
Wilks'
Lambda
0.031
2 through 4
Wilks' Lambda
Chi-square
df
Sig.
205.604
28
0.000
0.191
97.804
18
0.000
3 through 4
0.880
7.572
10
0.671
4
0.966
2.069
4
0.723
 Structure matrix table
The structure matrix indicates the relative importance of the predictors. The table
shows the correlations of each variable with each discriminate function. For Function 1,
Fmin and Fc, Fmax and Fk were positively correlated, as was Fmax for Function 2. This
indicated that Fmin is the predictor that maximally separate bat echolocation calls. This is
followed by Fc, Fmean, Fmax and Fk follow respectively.
Table 10: Structure matrix table
Structure Matrix
Function
Fmin
Fc
Fmean
Fmax
Fk
Sc
Dura
Tca
Tka
S1
1
0.680*
0.653*
0.646*
0.613*
0.601*
0.003
-0.102
-0.073
0.033
-0.042
2
-0.507
-0.513
-0.466
-0.394
-0.424
0.840*
0.760*
0.738*
0.612*
-0.059
3
0.048
0.056
0.015
-0.031
-0.019
0.108
-0.421
-0.440
-0.259
0.104
4
0.418
0.382
0.476
0.545
0.524
-0.119
-0.092
-0.095
0.203
0.929*
*. Largest absolute correlation between each variable and any discriminant function
a. This variable not used in the analysis.
Papadatou et al., (2008) and Parsons and Jones (2000) found terminal frequency as
the most important variable in most of their discriminant functions.
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
 Classification table
Overall, 69.7% of the echolocation calls were correctly classified into the different
groups, exceeding the value for classification based on chance (33.3%). At the individual
group level, 52.6% of calls of Scotophilus dinganiiwere correctly classified, 75.5% of
Scotophilus leucogaster,70.0% of Mops niveiventer, 55.6 % of Mops condylurus, 93.8%
of Chaerephon major (Table 11).
About 47.4% of calls of Scotophilus dinganii were misclassified as calls of Scotophilus
leucogaster while 25.0% of calls of Scotophilus leucogaster were misclassified as
belonging to Scotophilus dinganii. For Mops niveiventer, 30.0% of their calls were
misclassified as belonging to Mops condylurus. For Chaerephon major, 6.3% of their
calls were classified as belonging to Scotophilus dinganii(Table 11).
Table 11: classification table
Classification Results
Predicted Group Membership
species
S.
dinganii
% S. dinganii
S.leucogaster
M.niveiventer
M.condylurus
C. major
52.6
25.0
0.0
0.0
6.3
S.
M.
leucogaster niveiventer
47.4
75.0
0.0
11.1
0.0
.0
0.0
70.0
33.3
0.0
Total
M.
C.
condylurus major
.0
0.0
30.0
55.6
0.0
.0
0.0
.0
.0
93.8
100.0
100.0
100.0
100.0
100.0
69.7% of original grouped cases correctly classified.
 Canonical discriminant function plot
The plot of mean canonical scores and the canonical discriminant functions (Fig. 37)
demonstrates that the species groups are well separated in multidimensional space. It can
be observed that Function 1 mostly separate the calls from Mops condylurus and Mops
niveiventer which are two closely related species from those of Scotophilus dinganii and
Scotophilus leucogaster which are also closely related. Then function 2 mostly separate
Mops species and Scotophilus species from Chaerephon major.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Figure 37: Canonical discriminant functionsplot
Figure 37 shows the groups centroids of Scotophilus dinganii (forearm length 4957mm) and Scotophilus leucogaster(forearm 43- 51mm), are almost on the same spot,
indicting that calls parameters of these morphologically similar species are almostthe
same. Their calls are different from the calls of Mops condylurus (forearm 45-50mm) and
Mops niveiventer (forearm 44-47mm) which are species that are smaller than the
Scotophilus species but are morphologically similar to each other. The calls of
Chaerephon major forearm(42-44mm) are distinct from the Scotophilus species and the
Mops species. This goes to confirm the fact that closely related species, with similar
morphology and/or ecology may show convergent evolution of their call features and
hence similarities in their echolocation calls (Papadatou et al., 2008) and Parsons and
Jones (2000).
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Some of the 13 species of bats found in the Maroua area have been studied in
other part of Africa and their echolocation call parameters published.
Scotophilus dinganii was the largest bats captured during the study. This species
recorded calls with a maximum frequency of 58.5±8.9kHz. This is higher than the peak
frequency of 33.4±1.4kHzrecorded by Taylor et al., (2005) for individuals from St. lucia,
kwazulu natal south Africa. These differences can be due to differences in recording and
analysis techniques, habitat (clutter or open), and distance from the detector and humidity of
air (Kalko and Schnitzler 1993). Intraspecific variation of echolocation calls can also be due
to differences in sex (Jones et al., 1992) and age (Masters et al., 1995).Scotophilus
leucogaster is smaller and is usually distinguished from the Scotophilus dinganii by the
white color of it venter. This species recorded a maximum frequency at 55.7±4.3kHz. These
species can thus be distinguished from each other by their maximum frequency. Both species
produce echolocation pulses that are broadband, curved FM/QCF calls with an initial steep
FM sweep that ends with a QCF (Table 6). All FM/QCF are expected to forage mainly in
open spaces (Vaughan et al., 1997) because FM/QCF calls are suitable for use in open
environments with some obstacles (Simmons et al., 1979).
For the molossid bats, Mops condylurus recorded a maximum frequency 39.2±6.
kHz. This is much higher than the peak frequencies of 26-35 kHzrecorded in Mozambique
by Monadjem (2010b). Chaerephon pumilus recorded a maximum frequency of
44.2±3.4kHz. This was much higher than peak frequencies recorded in other parts of Africa.
The
peak
frequency
is
25.6±1.7
kHz
in
Kivoko
Kenya
(Taylor
et
al.,
2005);22.7±3.3kHzfrom Amani Nature Reserve in Tanzania (Aspetsberger et al.,2003); 32.9
± 4.5 kHz from Mlawula Swaziland and maximum frequencies of 43.0 ±1.0 kHz,28.7± 1.8
kHz and 28.7± 2.5 kHz in three different localities around Durban south Africa (Taylor
1999) . All molossid bats in this study produced FM calls.
The maximum frequency of Rhinolophus fumigatus was 62.6 kHz, which is higher
than the peak frequency of 54 kHz recorded from a single male in Mozambique by
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
Monadjem et al., (2010d). Schoeman and Jacobs (2008) also recorded a peak frequency of
53.7 kHz from South Africa. It can be observed that there is geographical variation in the
echolocation call parameters. This means that studies that use characteristic echolocation
calls to attempt the identification of species must make sure they compare them to calls
of known individuals of the same region. Furthermore, the rate of correct classification
by DFA was comparable to those achieved by other studies that have tried to use DFA to
classify calls from individual bats from known species.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
CONCLUSION AND PERSPECTIVES
Descriptions of echolocation call are important because they can be used to
investigate theecology and habitat use by bats and to supplement species
inventoriesbased on traditional capture methods. The descriptions we present here are
essential prerequisites to future investigations. This study has demonstrated the additional
contribution that acoustic sampling can make to survey and inventory for clarifying the
bats of Cameroon in general and the Far-north region in particular.
This study enabled us to increase the number of insectivorous bat species recorded in
the Maroua area from 15 to 18 by the traditional mist netting technique. Recording of
echolocation calls from these 13 species enabled us describe the call typed made by these
bats as either FM, FM/QCF and FM/CF/FM types. The visual sonogram displayed using a
zero-crossing period meter provided more information about the echolocation calls.
This information includes parameters such as minimum and maximum frequencies, call
shape, and call duration, which then may be used for qualitative species identification.
Subjecting the call characteristics of five species whose calls are described for the first time,
to a DFA, revealed overall correct classifications of 69.7%.The DFA shows that it is possible
to separate bats by their calls.It brought out the parameters that highly predict group
membership as the minimum frequency (Fmin) of calls. The successful description
echolocation calls from five species and our discriminant analysis provided a highidentification performance, potentially offering a tool for future acoustic surveys in the
Maroua area. Before the insectivorous bats in this region could be identified, using their
echolocation calls the model need to be standardized by recording the same species in all
environments in which the species can be found. It is for this reason that we are making the
following recommendations:
 The recording of the same insectivorous bat species in different environment of the
region in other to account for geographical variation.
 To ensure that many more individuals‟bats are used in future studies.
 To record the same bat species under different conditions such as hand release,
leaving the roost and in free flight.
Masters II Dissertation, University of Maroua (E.N.S)
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The Characterisation of Echolocation Signals of Insectivorous Bats in the Far-north
Region of Cameroon
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