Podoces, 2012, 7(1/2): 21–32
PODOCES
2012
Vol. 7, No. 1/2
Journal homepage: www.wesca.net
Diet Composition of the Barn Owl Tyto alba (Aves: Tytonidae) and Spotted
Owlet Athene brama (Aves: Strigidae) Coexisting in an Urban Environment
A. Mohamed Samsoor Ali1,2*& R. Santhanakrishnan1
1) Department of Zoology, Saraswathi Narayanan College, Perungudi, Madurai - 625 022, Tamil Nadu, India
2) Present Address: Environmental Impact Assessment Division, Sálim Ali Centre for Ornithology and Natural
History (SACON), Anaikatty, Coimbatore - 641 108, Tamil Nadu, India
Article Info
Original Research
Received 17 October 2012
Accepted 7 February 2013
Keywords
Arthropods
Barn Owl
Diet
Food niche overlap
Small mammal
Spotted Owlet
Abstract
The comparative diet of the Barn Owl Tyto alba and the Spotted Owlet
Athene brama were studied in an urban habitat of Madurai District, Tamil
Nadu, Southern India, during January–December 2008. Regurgitated
pellets of these two owl species were analysed to understand their dietary
composition. The diet of the Barn Owl mainly comprised small mammals
such as Suncus murinus (51.9%) and Rattus rattus (28.6%), while the diet
of the Spotted Owlet comprised mostly arthropods (84.9%); Coleoptera
(40.9%) and Orthoptera (32.4%). Food niche overlap between the Barn
Owl and the Spotted Owlet in overall diet was 6.5%, which indicated very
low degree of overlap.
1. Introduction
The Barn Owl Tyto alba (Scopoli, 1769) and
the Spotted Owlet Athene brama (Temminck,
1821) are known to coexist and use the same
habitat in southern India. Since these two
species are small mammal predators and known
to live together, they are suitable species for
studying resource partitioning and ecological
segregation. Coexisting species usually depend
on different requirements among the total
resources available to them. The diversity of
prey items taken by different predator species
constitutes ecological studies of sympatric or
coexisting species. Studies on food partitioning
are relatively scarce for raptors, and especially
owls in India, but considerable reports are
available regarding coexisting owls in various
geographical ranges (Georgiev 2005, Scheibler
2007, Riegert et al. 2009, Nadeem et al. 2012).
* Corresponding: [email protected]
The Barn Owl and the Spotted Owlet were
studied independently by various authors in
different parts of India and thus far, no attempt
has been made to study the above coexisting
owls in any particular area.
The Barn Owl, a widely distributed,
resident, and nocturnal raptor in India, is
closely associated with human-made structures
and agriculture (Marti et al. 1979, Kahila et al.
1994, Santhanakrishnan 1995). The Barn Owls
are often found in close proximity to humans,
and their occurrence is strongly associated with
the presence of buildings with suitable places
for roosting or nesting (de Bruijn 1994,
Shawyer 1994). Its diet consists chiefly of small
mammals, particularly rodents, but birds,
reptiles, amphibians and insects are also eaten
(Santhanakrishnan 1995, Mushtaq-ul Hassan et
al. 2004, Sommer et al. 2005, Leonardi & Arte
2006, Neelanarayanan 2007a). Extensive
studies have been conducted on the nesting and
feeding habits of the Barn Owl in many parts of
21
Diet composition
omposition of Barn Owl and Spotted Owlet – Ali & Santhanakrishnan
the world (Roulin 2002, Altwegg et al. 2003,
Haralambos et al.. 2005) but little is known on
the ecology of this species in south
outh-east Asia,
particularly in India. Available literature on
Indian Barn Owls focuses mainly on nest-sites
nest
(Nagarajan et al.. 1995), utilization of manman
made nest boxes (Neelanarayanan et al.
al 1995),
sexual dimorphism (Kanakasabai et al
al. 1996),
nestling growth patterns (Nagarajan et al. 2002)
and diet composition (Neelanarayanan 2007a,
b).
The Spotted Owlet is the most common
small-sized
sized (Ali & Ripley 1983) and least
studied owl species in India.
a. Spotted Owlets are
nocturnal and roost in the day under thick,
shady vegetation, cavities in tree, human-made
human
structures, including functional or nonnon
functional irrigation wells and crevices found in
rock cliffs (Santhanakrishnan et al. 2010a). It is
a generalist predator that feeds on diverse prey
such as rodents, bats, small birds, reptiles,
amphibians and invertebrates like insects,
annelids, scorpions and molluscs (Jain &
Advani 1984, Kumar 1985, Jadhav &
Parasharya 2003, Pande et al. 2004, 2007).
The present study focused on investigating
investigat
the diet of the Barn Owl and the Spotted Owlet
in an urban habitat simultaneously. Our aim
was to compare the dietary composition and
food niches of these two owl species over a
period of one year (January–December
December 2008) in
the urban environment of Madurai District,
Tamil Nadu, southern India.
2. Study Areas and Methods
2.1. Study areas
This study was conducted in the Madurai
District of Tamil Nadu, southern
outhern India (Fig. 1).
Topographically, the area is mostly flat with a
few hilly tracts. Madurai, lies between 9°56' N
and 78°07' E, is situated on the banks of the
River Vaigai. The climate is dry and hot, with
rains during October to December (northeast
monsoon). During our research,
research summer
temperature
emperature reached a maximum of 40°C and a
minimum of 26.3°C, while winter temperature
reached a maximum of 22.5°C and minimum of
19.7°C. The average annual rainfall is about
850 mm. Paddy is the predominantly cultivated
crop in the study area; however other
oth crops
such as sugarcane, banana, jasmine, betle vine,
groundnut and sorghum are also cultivated in
different regions.
22
The regurgitated pellets of both owl species
were collected in two different places situated
at the middle of the city of Madurai South
Taluk,
aluk, surrounded by houses, shops and other
human-made
made structures. The roost
roost/nest sites of
the Barn Owl were located in Sout
South Krishnan
Temple (9°54'50.65˝N, 70°07'01.46˝E). A pair
of the Barn Owls was spotted in the fifth
opening of the temple tower. The temple tower
provided a series of steps inside that provided
easy access to the owls. Also a roost
roost-site of the
Spotted Owlet was located in Thirumalai
Naikar Mahal (9°54'53.89˝N, 70°07'20.39˝E).
A pair of the Spotted Owlets was located in a
roof of building
ng and the pellets were recovered
beneath the building.
Fig. 1. Map of India, Tamil Nadu and Madurai District
(Map not to scale).
2.2.. Pellet collection and analysis
The roost-site / nest-sites
sites of both species were
visited twice a month from January 2008 to
December 2008 for the collection of the pellets.
Fresh pellets were collected separately during
each visit and pleced in plastic bags along with
tags indicating the species of owl, site name and
date of collection before being brought to the
laboratory.. Pellets were kept at 70°C in a hot air
oven for 24 hours to kill the associated
invertebrates.
Podoces, 2012, 7(1/2): 21–32
The length and width of owls pellets
collected were first measured using a Vernier
Caliper (with an accuracy of 0.05mm). The
samples were then weighed using electronic
balance with accuracy to 0.01 g. Pellets were
analysed following Schueler (1972) and Yalden
(2003). At the time of analysis, each pellet was
put in warm water or 3% Sodium Hydroxide
solution for softening. The pellet materials were
carefully opened up using tweezers. During
pellet examination, skulls, bones, feathers,
beaks and insect remains were separated out
first for identification. For studying seasonal
variations in the diets of the two owl species,
four seasons of a year namely post-monsoon
(January–March), summer (April–June), premonsoon (July–September) and monsoon
(October–December) were recognised.
2.3. Prey identification
Mammalian prey items were identified to
species level by comparing their bony remains
(e.g. skulls, mandibles) with museum
specimens collected from the same study area.
Birds, reptiles and amphibians were identified
by their feathers, beaks, skulls, synsacrum,
mandibles
and
parasphenoid
processes
(Naranthiran 1989, Daniel 1992, Daniels 2005).
We were not able to identify the bats, birds and
amphibians down to species level. Arthropod
prey items were identified up to order level on
the basis of undigested anatomical pieces such
as heads, mandibles, wings, legs, stings and
body rings (Naranthiran 1989, Yalden 2003,
Asokan et al. 2009). Most of the remains of
bats, birds, lizards and frogs were not intact.
2.4. Biomass estimation
The biomass of the prey of all mammalian
species recovered from the pellets were
estimated using a standard log-log regression of
right mandible length as a function of body
weight
following
Hamilton
(1980),
Santhanakrishnan
(1987,
1995)
and
Neelanarayanan (2007b). For this study, the
locally available mammalian species such as
House Rat Rattus rattus, Lesser Bandicoot Rat
Bandicoota bengalensis, Indian Field Mouse
Mus booduga and Grey Musk Shrew Suncus
murinus and their corresponding log-log
regression values for the calculation of biomass
were used as described by Santhanakrishnan
(1995).
2.5. Data analysis
Magurran (1988) was followed to assess and
compare the diversity in the diet of two owl
species by using species richness (S),
Shannon’s index (H’), and Peilou’s evenness
(E) indices. Food niche breadth (NB) was
estimated according to Levins (1968): NB =
(∑Pi2)–1, where, Pi is the proportion of prey i in
the food. The food niche overlap values
between two owl species were calculated by
Pianka’s index (Pianka 1973): O = ∑PijPik/
√∑Pij2 Pik2 where, Pi is the proportion of prey
species i in the diet of predator j and k
respectively. A value of 0 means no overlap and
1 means complete overlap. Kruskal Wallis
ANOVA was used to estimate the variation of
the prey remains between seasons. Data are
presented as mean ± SD. The MINITAB
(version 13.1) statistical software was used for
the statistical analyses.
3. Results
3.1. Pellets
Fresh Barn Owl pellets were dark green in
colour and covered with mucous. Pellets were
compact and had many bones (Fig. 2). A total
of 402 Barn Owl pellets were collected during
the study period. The average pellet length
(N=213) was found to be 3.7 ± 0.88cm (range:
1–8cm), width (N=213) of pellet was 2.5 ±
0.53cm (range: 0.8–4cm) and the average dry
weight of pellet (N=98) was found to be 3.3 ±
1.23g (range: 1.2–6.9g). The number of prey
items per pellet varied from one to seven with
the mean of 1.3±0.98 prey per pellet.
The regurgitated pellets of the Spotted
Owlets were in different size and shapes (Fig.
3). The fresh pellets were compact and dark in
colour because they contained masses of
undigested material, mostly insects. The
average length of the Spotted Owlet pellet
(N=310) was 2.7 ± 0.23cm (range: 2.2–3.3cm)
and width (N=310) was 1.4 ± 0.13cm (range:
1.1–1.8cm). The mean weight of the 111 pellets
was 0.39 ± 0.77g (range: 0.11–0.89g). The
mean number of prey items per pellet was 8.3 ±
2.45 (range: 3–19).
23
Diet composition of Barn Owl and Spotted Owlet – Ali & Santhanakrishnan
3.2. Diet of the Barn Owl
From all collected pellets, a total of 567
prey items could be distinguished with a
total mammalian biomass of 30,153 g
(Table 1). The Barn Owl fed on
insectivore mammals, rodents, bats,
lizards, frogs and insects. Six small
mammalian species comprised 89.7% of
all prey recorded from the study area.
Among the mammals, the Suncus
murinus (51.9%) was the most dominant
prey species in the diet of the Barn Owl,
followed by rodents, Rattus rattus
(28.6%) and Mus booduga (4.8%). The
proportion of insects in the diet was 3.4%
and other prey items were formed less
than 3%. Among the mammalian biomass
consumed by the Barn Owl, rodents
constitute 58.4% of the diet and that of
Suncus murinus was 41.6% (Table 1).
Fig. 2. Various shapes and sizes of the Barn Owl pellets recorded
in Madurai District, Tamil Nadu, Southern India.
Fig. 3. Various shapes and sizes of the Spotted Owlet pellets
recorded in Madurai District, Tamil Nadu, Southern India.
24
3.3. Seasonal diet of the Barn Owl
A total of 131 prey items were identified
from the analysis of 89 pellets in the
post-monsoon. Small mammals were
main prey items (90.2%) of the Barn
Owl. The Suncus murinus was
predominant prey species among small
mammals which accounted for 63.6% of
the total number of the prey individual
and 67.2% of their biomass. The Suncus
murinus was followed by Rattus rattus
(15.0%, 30.1%), Mus booduga (9.3%,
2.7%) and frogs (3.1%). The contribution
of other prey species such as bats, birds,
lizards and insects was less than 3%. The
Bandicoota bengalensis was absent in the
post-monsoon diet of the Barn Owl
(Table 2).
Podoces, 2012, 7(1/2): 21–32
Table 1. Prey frequencies (%) and biomass (%) consumed by the Barn Owl and Spotted Owlet in Madurai
District, Tamil Nadu, Southern India.
Prey items
Small mammals
Insectivores
Suncus murinus
Rodents
Bandicoota bengalensis
Rattus rattus
Mus booduga
Bats (Chiroptera)
Birds
Lizards
Frogs
Arthropods
Coleoptera
Orthoptera
Hemiptera
Diptera
Hymenoptera
Lepidoptera
Arachnida (Scorpions)
Unidentified items
Total Number and Estimated
biomass (g)
Barn Owl (N=402)
%
%
Total
Number
Biomass
Number
Spotted Owlet (N=310)
%
%
Total
Number
Biomass
Number
51.9
41.6
294
2.8
34.7
72
2.3
28.6
4.8
2.1
1.8
0.4
1.8
3.4
53.5
1.5
-----
13
162
27
12
10
2
10
0.5
3.1
1.2
--4.5
--
3.6
58.9
2.8
----
13
79
31
--115
--
3.4
------3.2
100
--------30153
19
------18
567
40.9
32.4
3.9
1.7
2.3
2.2
1.5
3.0
100
--------4125
1053
836
100
44
60
58
38
78
2577
Table 2. Seasonal changes in frequency (N%) and biomass (B%) of consumed prey items in the diet of Barn Owl
in Madurai District, Tamil Nadu, Southern India.
Prey items
Small mammals
Insectivores
Suncus murinus
Rodents
Bandicoota bengalensis
Rattus rattus
Mus booduga
Bats (Chiroptera)
Birds
Lizards
Frogs
Insects
Coleoptera
Unidentified items
Number of pellets
Total prey items
Mean prey/pellet
Estimated biomass (g)
Post-monsoon
%N
%B
Summer
%N
%B
Pre-monsoon
%N
%B
Monsoon
%N
%B
63.6
67.2
36.2
48.5
52.1
39.3
56.4
28.9
0.0
15.0
9.3
2.3
1.6
0.4
3.1
0.0
30.1
2.7
-----
2.9
41.3
0.0
2.2
2.9
0.0
2.9
3.3
48.2
0.0
-----
0.7
32.5
5.6
0.0
0.7
0.0
1.4
1.0
58.4
1.3
0.0
----
5.2
25.0
4.5
3.8
1.9
0.0
0.0
7.2
61.8
2.1
-----
0.8
3.9
---
7.2
4.3
---
5.6
1.4
---
0.0
3.2
---
89
131
1.1 ± 0.25
5151
95
138
1.2 ± 0.19
7056
89
142
1.1 ± 0.35
7851
129
156
1.3 ± 0.21
10095
25
Diet composition of Barn Owl and Spotted Owlet – Ali & Santhanakrishnan
Values
During the summer,
Prey species Richness Diversity Index (H') Evenness Index (E)
95 Barn Owl pellets were
analysed, yielding 138
9
prey
items.
The
8
consumption of small
7
mammals was decreased
6
(82.6%) in the summer
5
diet. The most preferred
prey both in number and
4
biomass was Rattus rattus
3
(41.3%, 48.2%) and
2
Suncus murinus (36.2%,
1
48.5%). The Bandicoota
0
bengalensis, bats, birds
and frogs were consumed
Post-monsoon
Summer
Premonsoon
Monsoon
almost
equally.
The
Seasons
proportion of coleopteran Fig. 4. Prey diversity in the diet of the Barn Owl in Madurai District, Tamil Nadu,
insects increased (7.2%) Southern India.
in summer, and Mus
booduga and lizards were
3.4. Diet of the Spotted Owlet
absent in the summer diet.
The remains of 2,577 prey items were found in
During the pre-monsoon, 89 pellets were
analysis of 310 pellets of the Spotted Owlet.
examined and again small mammals (90.9%)
The Spotted Owlet had eaten most frequently
were most dominant in the diet of the Barn
on arthropods (84.9%) followed by small
Owl. Numerically, Suncus murinus (52.1%)
mammals (7.6%) and lizards (4.5%). The
was most dominant prey species but Rattus
arthropods preyed upon are exclusively insects,
rattus was more important in term of the
predominantly Coleoptera (40.9%) and
biomass (58.4%). The consumption of Mus
Orthoptera (32.4%) followed by Hemiptera
booduga increased (5.6%) and the proportion of
(3.9%), Hymenoptera (2.3%), Lepidoptera
other prey items were low.
(2.2%) and Diptera (1.7%). Small mammals
Totally, 129 pellets were analysed during
were represented by two orders and four
monsoon, yielding 156 prey items. Like other
species. Among the mammalian prey, Rattus
seasons, small mammals were the principal diet
rattus was the dominant (3.1% in numbers and
and represented 94.9%. Among the small
58.9% in biomass) followed by Suncus murinus
mammals Suncus murinus
numerically
(2.8% in numbers and 34.7%in biomass) (Table
dominated (56.4%) in the diet but Rattus rattus
1).
contributed 61.8% biomass. The consumption
of Bandicoota bengalensis, Mus booduga, bats
3.5. Seasonal diet of the Spotted Owlet
and birds were increased during the monsoon.
A total of 511 prey items were recovered from
No lizards and insects were consumed during
the analysis of 60 Spotted Owl pellets in the
the monsoon.
post-monsoon. Arthropods were predominant
The consumption of Suncus murinus
(84.8%) in the diet while rest of it comprised
(Kruskal Wallis ANOVA: H=56.21, P<0.001),
small mammals (7.6%) and lizards (4.8%).
Mus booduga (H=123.5, P<0.0001), bats
Among the arthropods, the Spotted Owlet
(H=94.2, P<0.001) and birds (H=110.2, P<
preyed mainly on the Coleoptera (47.2%) and
0.0001) was significantly different between the
Orthoptera (24.4%). The Suncus murinus
seasons. Both prey diversity index (H') and
(3.6%) was a frequent mammalian prey species
evenness index (E) had its lowest value in
in the diet of the Spotted Owlet but Rattus
summer and its highest value was in monsoon
rattus contributed more biomass (50.3%; Table
(Fig. 4).
3).
26
Podoces, 2012, 7(1/2): 21–32
Table 3. Seasonal changes in frequency (N%) and biomass(B%) of consumed prey items in the diet of Spotted
Owlet in Madurai District, Tamil Nadu, Southern India.
Prey items
Post-monsoon
Summer
Pre-monsoon
Monsoon
%N
%B
%N
%B
%N
%B
%N
%B
3.6
40.2
0.9
55.6
4.9
27.7
3.6
38.0
Bandicoota bengalensis
Rattus rattus
Mus booduga
0.4
2.2
1.4
6.0
50.3
3.5
0.5
3.2
2.3
4.2
40.2
0.0
0.0
1.5
0.7
0.0
68.5
3.8
0.0
6.9
0.0
0.0
62.0
0.0
Lizards
4.8
--
4.9
--
1.2
--
5.2
--
Arthropods
Coleoptera
Orthoptera
47.2
24.4
---
39.6
36.7
---
35.4
40.1
---
41.7
28.1
---
Hemiptera
Diptera
Hymenoptera
Lepidoptera
4.0
2.2
2.0
2.6
-----
3.1
1.2
0.9
1.7
-----
4.6
2.8
3.3
2.1
-----
3.8
0.9
2.7
2.6
-----
Arachnida (Scorpions)
Unidentified items
Number of pellets
Total prey items
2.4
2.8
---
1.2
3.8
---
0.8
2.6
---
1.7
2.9
---
Small mammals
Insectivores
Suncus murinus
Rodents
Mean prey/pellet
Estimated biomass (g)
60
511
83
572
86
724
81
770
8.3 ± 3.25
984
6.9 ± 2.51
1008
8.4 ± 4.21
962
9.5 ± 4.17
1171
Overall, 572 prey items were identified in
the analysis of 83 pellets during summer. Again
arthropods remained dominant by numbers
(84.4%) but the biomass was mostly due to
Suncus murinus (55.6%) and Rattus rattus
(40.2%). Coleoptera (39.6%) and Orthoptera
(36.7%) were the most frequent among
arthropods. The proportion of Suncus murinus,
Coleoptera, Hemiptera, Diptera, Hymenoptera,
Lepidoptera and Arachnida decreased, while
that of Rattus rattus, Mus booduga, lizards and
Orthoptera increased in the diet.
Analysis of 86 pellets of the Spotted Owlet
during pre-monsoon revealed the presence of
724 prey items. The consumption of Arthropods
increased (89.1%) as compared to other
seasons. The proportions of Rattus rattus, Mus
booduga, lizards and Coleoptera decreased and
the proportions of Suncus murinus (4.9%) and
Orthopteran
insects
(40.1%)
increased
comparatively. The Rattus rattus (68.5%) had
the greatest portion in its diet in terms of
biomass. No Bandicoota bengalensis was eaten
in this season.
During the monsoon, 81 pellets were
examined, arthropods remained dominant by
numbers (81.5%), but the biomass was mainly
because of the presence of two mammalian
species, Rattus rattus (62.0%) and Suncus
murinus (38.0%). The proportions of
Orthoptera (28.1%) decreased and the
proportions of Coleoptera (41.7) and lizards
(5.2%) increased greatly. No Bandicoota
bengalensis and Mus booduga were consumed
during the monsoon season.
There was significant seasonal variations in
the diet of the Spotted Owlet for the prey items
such as Coleoptera (Kruskal Wallis ANOVA:
H=85.06, P<0.001), Orthoptera (H=185.3,
P<0.0001),
Hymenoptera
(H=158.3,
P<0.0001), lizards (H=65.52, P<0.001), Rattus
rattus (H=156.41, P<0.0001) and Mus booduga
(H=85.65, P<0.001). Diversity indices (H')
revealed that the greatest and lowest diet
diversity was during the summer and postmonsoon, respectively. The diet evenness index
(E) had the highest value in summer and lowest
value in monsoon (Fig. 5).
27
Diet composition of Barn Owl and Spotted Owlet – Ali & Santhanakrishnan
Food Overlap
Values
3.6. Comparison of diets
of two sympatric owl
Prey species Richness Diversity Index (H') Evenness Index (E)
species
14
The Barn Owl and the
Spotted Owlet consumed a
12
wide variety of prey items,
10
but the dominant prey taxa
were different between the
8
two owl species. The diet
composition of the Barn
6
Owl indicated that small
mammals remained the
4
dominant prey, making up
to 89.7% of their diet.
2
Among
these,
the
0
insectivore
mammal
Suncus murinus was the
Post-monsoon
Summer
Premonsoon
Monsoon
major
prey
species
Seasons
(constituting
51.9%),
Fig.
5.
Prey
diversity
in
the
diet
of
the
Spotted Owlet in Madurai District, Tamil
followed by the rodent
Nadu, Southern India.
species
Rattus
rattus
(28.6%).
Arthropods
0.1
clearly dominated the diet
of the Spotted Owlet,
0.08
constituting 84.9%, along
with a lesser amount of
0.06
small mammals (7.6%) and
lizards (4.5%). Among
0.04
arthropods,
the
Coleopteran beetles and
0.02
Orthopteran insects were
the most dominant prey
0
items throughout the year.
Post-monsoon
Summer
Pre-monsoon
Monsoon
Both
species
were
dependent
significantly
Seasons
more on the biomass of
Fig. 6. Seasonal changes in food overlap of the Barn Owl and Spotted Owlet
Rattus rattus. The niche inhabiting in Madurai District, Tamil Nadu, Southern India.
breadth of the Barn Owl
was considerably wider
the pellets were different than the reports by
(2.8) than the Spotted Owlet (2.3). The food
Buxton & Lockley (1950; 110×50 mm), Glue
niche overlap between the Spotted Owlet and
(1967; 45×26 mm) and Nadeem et al. (2012;
the Barn Owl in overall diet composition was
48.2×38.2 mm). In agreement, Hardy (1977)
6.5%, which indicated very low degree among
stated that the size of the pellets significantly
both species. The low degree of food overlap
varied, which depended on the composition of
was also found in different seasons in both
the diet and the size as well as nutritive value of
species (Fig. 6).
taken prey. The mean number of prey per pellet
4. Discussion
The size of the Barn Owl pellets in this study
area were similar to those reported by other
workers (Glue 1967, Santhanakrishnan 1995,
Alvarez-Castaneda et al. 2004, Mahmood-ul
Hassan et al. 2007a). The length and width of
28
averaged 1.3 for the Barn Owl, which was
similar to the average given by other workers
(Neelanarayanan 2007a, Travaini et al. 1997,
Bellocq 1998, Charter et al. 2007, Magrini &
Facure 2008). The average measurements of
pellet sizes reported for the Spotted Owlet in
Podoces, 2012, 7(1/2): 21–32
other studies (Tariq et al. 2003, Pande et al.
2004, Nadeem et al. 2012) were different from
our findings. Mean number of prey items per
pellet was 8.3 for the Spotted Owlet, which
compares favourably with mean given by
Naranthiran (1989) and Pande et al. (2007). In
contrast, Mahmood-ul Hassan et al. (2007b)
reported the mean number of prey as being only
1.6 prey items in Pakistan. The number of prey
per pellet of the Spotted Owlet was higher than
that of the Barn Owl possibly because much
larger numbers of insects were consumed by the
Spotted Owlet.
Several investigations on the diet of the Barn
Owl in different geographical regions
confirmed that small mammals were the main
components of the diet (Marti 1974, Gubanyi et
al. 1992, Pezzo & Morimando 1995, Travaini et
al. 1997, Alivizatos & Gounter 1999, Love et
al. 2000, Bose & Guidali 2001, Mushtaq-ulHassan et al. 2004, Alivizatos et al. 2005,
Leonardi & Arte 2006, Mahmood-ul-Hassan et
al. 2007c, Magrini & Facure 2008, Nadeem et
al. 2012) and our results also indicated a similar
pattern. Numerically, the Suncus murinus
(51.9%) was the main contributor while in
terms of biomass, the Rattus rattus (53.5%) was
the main prey in the diet of the Barn Owl. In
contrast to our findings, Santhanakrishnan
(1995) and Neelanarayanan (2007a) reported
that field rodents of agricultural value such as
Bandicoota bengalensis, Tatera indica,
Millardia meltada and Mus spp. were
consumed predominantly and that Suncus
murinus constituted only 20% of the diet in the
Cauvery Delta region, Tamil Nadu, India. In the
present study, the regurgitated pellets of both
owl species were collected in an urban
environment (dominated by human habitations).
Therefore, Suncus murinus and Rattus rattus
were the predominant prey in the Barn Owl
diet.
Barn Owls consume negligible amounts of
birds. As other studies indicate, this may be
because Barn Owls may concentrate on birds
when other prey are scarce (Alivizatos et al.
2005, Leonardi & Arte 2006). Small
proportions of lizards and frogs were recorded
in the diet of the Barn Owl in this study. Some
authors report these prey in the diet of the Barn
Owls (Sommer et al. 2005, Neelanarayanan
2007a). The presence of insects in the diet of
the Barn Owls have been described by many
authors in different locations (Travaini et al.
1997, Alvarez-Castaneda et al. 2004, Alivizatos
et al. 2005, Charter et al. 2007). Small fractions
of Coleopteran insects were recorded in the diet
of the Barn Owl in the present study.
The consumption of small mammals in the
diet of the Barn Owls among the seasons was
more or less similar, but changes were noticed
among the prey species within the small
mammals. The main prey component of the
Barn Owl diet, Suncus murinus was taken at
lowest frequency during the summer season. In
this period, the proportion of Rattus rattus,
Bandicoota bengalensis, birds and insects
increased. This seasonal trend was also
documented by other authors (Barbosa &
Benzal 1996, del Guasta 1999, Debrot et al.
2001, Mahmood-ul-Hassan et al. 2007c). The
changes in prey composition in our study area
may reflect the opportunistic hunting strategy
of the Barn Owl in relation to the abundance
and availability of prey items (Marti 1972,
Barbosa & Benzal 1996, del Guasta 1999, Bose
& Guidali 2001, Mahmood-ul-Hassan et al.
2007c).
The pellet analysis demonstrates that the
Spotted Owlet is not a specialist, with a diet
composition of 84.9% invertebrates and 12.1%
vertebrates. In general, insects (83.4%) play an
important part of the Spotted Owlet diet.
Among insect prey, Coleoptera (40.9%) and
Orthoptera (32.4%) formed important insect
prey. Our results were similar to those
documented for the Spotted Owlet in India and
Pakistan (Jain & Advani 1984, Kumar 1985,
Naranthiran 1989, Beg et al. 1990, Jadhav &
Parasharya 2003, Pande et al. 2004, 2007, Shah
et al. 2004, Mahmood-ul-Hassan et al. 2007b).
Mammals constituted only 7.6% of the total
prey items. Rattus rattus and Suncus murinus
were the most common prey among mammals
and thus the Spotted Owlet plays an important
role in pest control in human environments.
Similar small mammal prey was reported for
the diet of the Spotted Owlet by other authors
(Jain & Advani 1984, Kumar 1985, Naranthiran
1989, Pande et al. 2004). Lizards and scorpions
were hunted throughout the year. The Spotted
Owlet foraged more on Coleopteran beetles
throughout the year, with its lowest proportion
during the pre-monsoon season. The decrease
was compensated by an increased proportion of
Orthoptera, Hemiptera, Diptera, Hymenoptera,
29
Diet composition of Barn Owl and Spotted Owlet – Ali & Santhanakrishnan
Lepidoptera and Suncus murinus. During the
monsoon season, the consumption of
Coleoptera, Rattus rattus and lizards increased
while a decrease in Orthoptera and other insect
prey was observed.
In conclusion, the diet composition of the
Barn Owl and the Spotted Owlet varied
throughout the year. The low dietary overlap
between the two owl species may be due to
their different body sizes. The Spotted Owlet is
smaller (80–100g) than the Barn Owl (400–
500g) and seems to prefer comparatively
smaller prey. The prey size selection of small
mammals in the study area indicated that the
Spotted Owlet had consumed 68% of the
mammals in the 1–20g weight class interval,
whereas the Barn Owls had selected mammals
with a preference on 1–60g weight class
interval up to 73% (Santhanakrishnan et al.
2010b, 2011). The observed differences
between the Barn Owl and the Spotted Owlet
diet in the study area may be caused by several
factors. Taken collectively, their body size, prey
availability, habitat type used for hunting prey,
and hunting techniques allow these owls to
minimise potential competition for food.
Acknowledgements
We thank the Ministry of Environment and Forests,
Government of India, New Delhi for providing
financial support. We are grateful to the Principal
and the Management of Saraswathi Narayanan
College, Madurai for having rendered facilities and
encouragements. We are also thankful to Mr. U.
Anbarasan and Mr. P. Muthukumar who assisted
with the fieldworks. We thank David H. Johnson
(Director – Global Owl Project) for his thoughtful
edits to an earlier version of this manuscript.
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