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Forest Resources and Wildlife Management
Forest Resources and Wildlife Management Publications
2009
Morphometries of White-browed
Sparrow-Weavers Ploeepasser mahali
in south-western Zimbabwe
Leitner, Stefan
http://ir.nust.ac.zw/xmlui/handle/123456789/555
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OSTRICH 2009, 80(2): 9!}-102
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OSTRICH
ISSN 0030-6525 EISSN 1727-947X
dol: 10.298910STRfCH.2oo9.80.2.6.833
Morphometries of White-browed Sparrow-Weavers Ploeepasser mahali in
south-western Zimbabwe
Stefan Leitner1 ,2*, Peter Mund y 3 and Cornelia Volgt1 ,3
Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, D-82319 Seewiesen, Gennany
2 School of Biological Sciences, Royal Holloway University of London, Egham, Surrey, 7W20 OE>(, UK
Department of Forest Resources and Wildlife Management, National University of Science and Technology, Bulawayo, Zimbabwe
• Corresponding author, e-mail: [email protected]
1
3
This paper describes size and body condition of individuals in a population of the cooperatively breeding White-browed
Sparrow-Weaver Plocepasser mahali in south-western Zimbabwe in relation to the birds' social status within their colony.
We undertook measurements and observations of colour-ringed individuals during two successive breeding seasons. Each
colony was organised into a dominance hierarchy, with a single dominant breeding pair and male and female subordinates.
Our results showed that males were generally larger than females in body mass, wing and bill length. Within each sex size
was not significantly related to dominance status. Body condition did not vary by sex, age or status.
Introduction
The White-browed Sparrow-Weaver Plocepasser mahali
is a cooperatively breeding songbird belonging to the
family of weaverbirds (Ploceidae). Its distribution ranges
from the north-eastern to the southern parts of Africa. The
subspecies P. m. mahali that we investigated is a common
resident bird in southern Zimbabwe and in South Africa
(du Plessis 2005). It inhabits semiarid Acacia and mopane
Colophospermum mopane savanna woodland. Birds live
in groups of 2-10 individuals in year-round territories with
a dominant breeding pair and male and female subordinates (Collias and Collias 1978, Lewis 1982, Ferguson
1988). Previous studies suggested that dominance rank
was closely correlated with body mass in females during
breeding and that the most dominant male of the group was
usually the heaviest bird (Collias and Collias 1978, Earle
1983). However, no statistical comparisons have been
made. The purpose of the present study was to identify
whether, and by how much, birds differed in morphological
measurements and mass according to their social status.
Materials and methods
Study area
Our stUdy site was in the south-western part of Zimbabwe,
about 60 km south-east of BUlawayo near the village of
Esigodini, 20°08'-20°14' Sand 28°56'-29°0' E (Figure 1).
This area mainly consisted of farmland at altitudes ranging
from 1 120-1 235 m in the transition zone between
middleveld and highveld. The landscape was characterised
by Acacia savanna, bushy hillsides, and open grassland.
Data were collected in two consecutive years during the
rainy season: from 25 January to 19 March 2000, and from
30 January to 1 March 2001. We conducted the study on
two commercial farms, which were 10 km apart from each
other (Figure 1). In 2000 and 2001 we identified 28 and 27
White-browed Sparrow-Weaver groups, respectively, on
these study sites. Neighbouring groups were at least 40 m
apart. To determine territory size we measured the distance
between the outermost trees occupied by the respective colony and prepared 1: 1 000 draWings of the colony
boundaries. Drawings were scanned using HP Scan Jet
6400 connected to a PC. The region of interest was delineated on the screen with the computer mouse and the areas
were calculated by a built-in function of SPOT 3.2.4 software
(Diagnostic Instruments, Burroughs, Minnesota).
a
Study animals
Birds were captured with mist nets during the day and
with a special trap after sunset to catch them inside their
roosting nests. Every bird caught had a unique combination of a numbered aluminium ring and two coloured plastic
rings placed on its legs. Birds were sexed according to
the coloration of their beaks: black bills in adult males and
horn-coloured in adult females (Earle 1983). Birds were
considered immature when bill colour was not yet uniform
and the sex could not be identified unequivocally. Details
on the identification of the social status of individuals have
been described elsewhere (Voigt et al. 2006). Morphological
measurements such as wing length, bill length, body mass,
as well as fat and muscle score, were obtained using
standard methods following a protocol of the bird banding
station at Vogelwarte Radolfzell (1995) of the Max Planck
Institute. Body mass was measured using a 100 g Pesola
spring balance (Pesola, Baar, Switzerland) with an accuracy
of 0.5 g, wing length (maximum chord) using a steel ruler
with an accuracy of 0.5 mm, and bill length (from feathers)
and tarsus length (from the notch on the metatarsus to
the top of the bone above the folded toes) using a calliper
Leitner, Mundy and Voigt
100
:
Fence
II
Gate
o
•
Zimbabwe
House
Colony in 2001
o
Colony in 2000
•
Colony in both years
.......
I
Intabanenda
/t:::J D.~
•
I.
-'...
_I
~o ~
(20·09' S, 29°00' E)
o
Ie
I
/
/
I
•
0
•
0
Figure 1: Schematic map showing the location of the two study sites on commercial farmland in south-western Zimbabwe and the location
of White-browed Sparrow-Weaver breeding colonies in the study sites in 2000 (open circles), in 2001 (filled circles) and in both 2000 and
2001 (shaded grey circles)
with an accuracy of 0.1 mm. For fat scoring we used a
scale (0-8) to estimate the visible fat deposit of the bird;
o indicated no fat, through to 8, which meant that the breast
muscle was not visible and the fat deposit covered the
entire abdomen. For muscle scoring we used a scale (0-3):
o meant sternum sharp, muscle hollowed, through to 3,
which meant that the sternum was almost not visible due to
fUlly developed musculature.
Statistical methods
All statistics were performed using Systat 11 software
(Systat Software, Chicago). Comparisons of morphological measurements according to sex, age and social status
were made by one-way analysis of variance with post-hoc
multiple comparisons (Tukey HSD test) and the significance
level was fixed at P < 0.05.
Results and discussion
Altogether, 111 White-browed Sparrow-Weavers were
captured (61 in 2000 and 50 in 2001), from which 90
were sexed by bill colour (Earle 1983), excluding the 21
immatures with non-uniform bill colour. Of the adult birds,
67 could be assigned a dominant or subordinate status (see
Table 1). Territory sizes ranged from 2500-10000 m' and
were slightly smaller than reported previously from another
study in northern Zimbabwe (Vemon 1983). Large colonies
persisted throughout both study years, whereas small
colonies were often abandoned after one breeding season.
The majority of groups persisted longer than one year.
As Figure 1 shows, groups can frequently be found in the
vicinity of buildings, roads and fences.
We compared each morphological measurement between
adult males and females of different social status and
immature birds. The analysis revealed significant differences in wing length, bill length and body mass (Table 1).
Post-hoc multiple comparisons showed that dominant
males had larger wing length (P = 0.0001) and body mass
(P = 0.003) than dominant females. Furthermore, both
groups of males had larger wing length than immature
birds (dominant male vs immature, P = 0.0001; subordinate vs immature, P = 0.001), and dominant males also
had larger bill length than subordinate females (P = 0.004).
However, within each sex the birds did not differ in size
according to their social status. Collias and Collias (1978)
reported a significant correlation between dominance rank
Ostrich 2009, 80(2): 99--102
101
Table 1: Comparisons of morphological measurements from Whlte-browed Sparrow-Weavers according to sex, age and social status (values
are the mean ± SD)
Status
N
Body mass (g)
Wing length (mm)
Tarsus length (mm)
Bill length (mm)
Fat score
Muscle score
Adult males
Dominant
Subordinate
26
13
47.4 ± 2.3
45.5 ± 2.7
103.2 ± 2.4
102.7 ± 2.0
25.4 ± 0.5
24.9 ± 0.7
15.0 ± 0.3
14.8 ± 0.5
3.1 ± 1.0
3.1 ± 0.9
1.9 ± 0.3
1.9 ± 0.4
Adult females
Dominant
Subordinate
20
8
44.0 ± 2.9
44.3 ± 2.7
100.2 ± 1.7
100.7 ± 1.8
25.1 ± 0.4
25.1 ± 0.6
14.7 ± 0.5
14.3 ± 0.5
3.3 ± 1.3
3.5 ± 1.3
1.9 ± 0.3
1.9 ± 0.4
Immatures
F statistics
21
43.6 ± 3.3
99.5± 2.6
24.9±0.7
14.6 ± 0.4
3.4 ± 1.0
1.9 ± 0.3
6.66-*
10.97*2.35
4.310.37
0.08
* P < 0.05, ** P < 0.01, *** P < 0.001
and body weight in three out of five colonies in a Kenyan
population but their analyses were not made according to
sex. Therefore a comparison with the results of our study
is difficult. Earle (1983) found that dominant males had
larger wing lengths than females; moreover, dominant
males were heavier than all other birds within the group and
breeding females were heavier than non-breeding females.
Our data, in contrast, showed no differences in body mass
between dominant and subordinate males (P = 0.293).
Within females we did not find a difference in body mass
either (P = 0.999), which may have been because we did
not sample dominant females just prior to egg-laying as
Earle (1983) did. Similar to his data, breeding males of the
group-living Green Woodhoopoe Phoenicu/us purpureus
were heavier than non-breeding males but they were also
significantly older (Radford and du Plessis 2004). So it is
possible that this factor explained the difference in body
size (AN Radford pers. comm.) For sparrow-weavers no
data on age structure of a population are available. The
only morphological predictor of social status found so far in
White-browed Sparrow-Weavers is testes size, being about
three times larger in dominants than in subordinates during
the breeding season (Voigt et al. 2007).
When we pooled all adults of both sexes, males differed
significantly from females in having larger wing length, bill
length and body mass (Table 2). Similar data were found by
Earle (1983) but due to large variation the differences were
not significant in his study. No sex difference existed in our
sample for tarsus length and muscle condition (Table 2).
Fat scores were insignificantly different across sexes, ages
and status (Table 1; P> 0.8), although on average females
and immatures scored higher than males. However, when
all adult males and females were pooled, females scored
significantly higher than males, though only just (Table 2;
P= 0.042).
The average measurements of the birds in our sample
were smaller in all dimensions than those from a study in
South Africa by du Plessis (2005): 1-2 rnm shorter in wing
length, 1 mm in tarsus length and nearly 2 g in mass). We
can not directly compare bill length, as it was measured
differently from our study. These data are in agreement
with Bergmann's rule, which proposes that within-species
body size is positively correlated with latitude and colder
climate (Bergmann 1847) and which has been confirmed
in other passerines from southern Africa, such as the Cape
Table 2: Comparisons of morphological measurements from adult male
(M; N = 43) and female (F; N = 47) White-browed Sparrow-Weavers
Measure
Body mass
(g)
Sex
M
F
Mean
46.9
44.4
SD
2.8
2.6
Range
39.5-54.0
37.5-52.0
t statistics
Wing length
(mm)
M
F
103.2
100.3
2.3
1.8
99-108
97-105
6.760 **
Tarsus length
(mm)
M
F
25.2
25.0
0.6
0.5
24.0-26.4
24.2-25.9
1.61
Bill length
(mm)
M
F
15.0
14.6
0.4
0.5
13.9-15.8
13.3-15.6
3.60"
Fat score
M
F
3.0
3.5
1.0
1.3
1.0-6.0
1.0--6.0
2.06*
Muscle score
M
F
1.9
1.9
0.3
0.4
1.0-2.0
1.0-3.0
0.58
4.41-*
* p.< 0.05, ** P < 0.01, *.* P < 0.001
Sparrow Passer melanurus (Slotow and Goodfriend 1996)
and the Dark-capped Bulbul Pycnonotus tricolor (Crowe
et al. 1981).
Acknowledgements - This research was supported by funding
from the Max Planck Society. We thank the Research Council of
Zimbabwe for permission to conduct this study. We are grateful to
W Wickler and the late R Hartley for support.
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Received March 2008, accepted September 2008
Editor: A Monadjem