Group size, sex and age composition of chital ( Axis axis) and sambar ( Rusa unicolor) in a deciduous habitat of Western Ghats

Abstract

Knowledge of the social structure of a population is important for a range of fundamental and applied purposes. Group characteristics and population structure of chital ( Axis axis) and sambar ( Rusa unicolor) were studied in a deciduous habitat of Mudumalai Tiger Reserve, Western Ghats, India, during 2008–2009. Vehicle transects were monitored monthly to gather information on group–size and age–sex composition of chital and sambar. The average mean group size and crowding for chital and sambar was 13.1 ± 0.5 ( n = 1020), 3.6 ± 0.2 ( n = 377) and 33.3, 11.0 respectively. The average adult male:adult female:fawn ratio was 63.4:100:22.3 ( n = 9391) and 43.9:100:23.7 ( n = 1023) in chital and sambar respectively. The mean group size of chital and sambar varied significantly between seasons (Kruskal–Wallis test, p = <0.001). Peak fawning season was observed from February to May for chital and May to August for sambar. Group's sex–age composition influenced group formation in both species between seasons at different level. Adult male and fawn were the important predicting variables of change in group size. Skewed female sex ratio was probably due to selective male predation by large predators. Although fawning occurred throughout the year, both species showed seasonality in fawning. The above mentioned patterns differed between species depending upon their ecological adaptation in foraging strategies and habitat preference.