POPULATION STRUCTURE OF NILGAI (BOSELAPHUS TRAGOCAMELUS) IN THE SEMI ARID REGION OF THE THAR DESERT

Abstract

The Thar Desert is spread over twelve districts of Rajasthan. It has divided into arid and semi arid region. Study of population structure of Nilgai (Boselaphus tragocamelus) was conducted in semi arid region near Jodhpur city by using the line transects and direct count methods. The nilgai adapt in dry and hot environmental condition of desert. Population of nilgai lives in small herd (group). The grouping behaviour minimize the threats and provides the safe environment for survive. Two types herd such as bisexual herd and all male herds were observed in the nilgai population. Bisexual herds were comprised of adult dominant male, recessive males, adult females, calves, sub adult males and sub adult females while all male herds were composed of males of different age groups. Mixed (bisexual) herd size generally varied from 2 to 7 individual in the study area. The sub adult males of mixed groups were discarded by the dominant male of mixed herd. The herd size was influenced by different factors such as human activities, availability of water
and food sources. The largest herd size was observed in monsoon while smallest herd size in summer season. Density of nilgai popula area was 0.54 individuals /sq km. The adult male to adult female sex ratio (1: 1.24) tilted towards the adult female while adult female to sub adult sex ratio (1: 1.16) bent in favour of sub adult. The nilgai is yearlong breeder but maximum calves were observed in monsoon season and natality rate was recorded 0.51 calves / female