Post by warsaw on Dec 18, 2012 8:57:28 GMT -9
Age and sex determination of gaur Bos gaurus (Bovidae) Lead [-]
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Mammalia 75 (2011): 151–155 2011 by Walter de Gruyter • Berlin • New York. DOI 10.1515/MAMM.2010.078
2011/067
Article in press - uncorrected proof
Age and sex determination of gaur Bos gaurus (Bovidae)
One reason why the gaur Bos gaurus is a poorly understood
species is because there are no reliable data to age and sex
individuals. We studied captive gaur for two years in Mysore
Zoo, India and Omaha Zoo, USA, and determined age-specific
differences in morphological features and physical
growth, by measuring shoulder height, of male and female
gaur. We fitted von Bertalanffy growth functions to the
shoulder height data and found maximum shoulder heights
of 175 cm and 147 cm for males and females, respectively.
This study ascertained for the first time that the greater the
amount of white on the horns of a gaur, the older it is, and
that the sexes can be distinguished based on horn shape and
size differences. We found that gaur aged 15 months and
below can be classified into three age classes, but are difficult
to sex. The sex of gaur aged 15–36 months is best determined
by a study of their horns. Adult gaur, greater than
three years, are easy to sex, but are difficult to classify into
single-year age classes and are reliably classified only into
two age classes for females and three for males.
Materials and methods
Captive populations with individuals of known age provide
the ideal setting to study age-specific morphological growth
patterns of a species. We studied India’s largest captive gaur
population housed in Mysore Zoo, Mysore, from November
2005 to August 2007, and the world’s largest captive gaur
population housed at Henry Doorly Zoo, Omaha, NE, USA,
in July 2006.
We compiled data and recorded (with photographs) the
morphological characteristics of 28 different individuals of
known age, 16 females (aged 2 weeks to 16 years) and 12
males (aged 3 weeks to 11 years), during the study period
in Mysore Zoo. We ascertained age-specific differences in
body and horn color and the growth of distinguishing features
such as dewlap and dorsal ridge in males. We established
the differences in length, size, and shape of the horns
using relative measurements from individuals of known age
in the photographs.We supplemented the morphological data with quantitative
data of the growth in shoulder height of gaur. We measured
the shoulder height (height on the dorsal ridge aligned vertically
with foreleg) of different aged gaur by (a) directly
measuring individuals photographed against scales painted
within their zoo enclosures, and (b) indirectly measuring the
relative heights of gaur photographed alongside individuals
that had been measured against scales. We collected a total
of 51 measurements (25 for females and 26 for males), 37
of which were from Mysore Zoo and 14 were from Henry
Doorly Zoo. The measurements were either the most reliable
one, or the mean of two to four, of an individual at a particular
age. This yielded data of females at 18 distinct ages
(between 2 weeks and 17 years) and of males at 17 distinct
ages (between 2 weeks and 10 years).
The von Bertalanffy function (von Bertalanffy 1938) was
fitted to the shoulder height data of both sexes. This function
has been used to fit physical growth data of other large herbivore
species including elephants, both Asian Elephas maximus
and African Loxodonta africanus (Hanks 1972,
Sukumar et al. 1988), and African buffalo (Sinclair 1977)
Results
Our observations provide the most detailed and comprehensive
data on the visual morphological differences between
male and female gaur. The changes in the visible morphology
of male and female gaur as they age, that can be used
to identify gaur by age and sex, are listed in Table 1 and
illustrated in Figure 1. Schaller (1967) was correct to classify
adult gaur into broad age-classes; we found that it is not
possible to age gaur into single-year age-classes beyond the
age of three years based only on visual morphological features.
The new and important result that emerged from this
study was that horn characteristics differences make it possible
to differentiate between the sexes of gaur above the age
of 15 months. Gaur above the age of three years are even
easier to sex (Table 1).
Growth in body size is similar in the sexes until the age
of 15 months, after which growth rates in males is greater
than in females (Figures 1 and 2). Although females appear
to attain 90–95% of their maximum shoulder height by three
years (Figure 2), they continue to grow in body mass and
probably attain their maximum body size by the age of six
years. Males continue to grow for a greater number of years
than females, attain their maximum shoulder height at
8–10 years (Figure 2), and probably attain maximum body
size by 10–12 years. Maximum shoulder height was found
to be 175 cm for males and 147 cm for females
www.resource-ecology.org/publ/2011_Ahrestani,Prins_AgeAndSexDeterminationOfGaur.pdf
