A Study of Vigilance Behaviour of Chital (Axis axis) in Pench Tiger Reserve, Madhya Pradesh

Abstract

Predation is an important agent of natural selection in animal communities and so vigilance behaviour has very high selection pressure acting upon it. During feeding bouts, unless plant density and biomass are high and food intake is limited only by the processing rates, herbivores tend to experience a trade-off between vigilance and feeding. Thus, vigilance as a behaviour pattern ought to be tightly regulated by the cost-benefit ratios. A study on vigilance behaviour of chital (Axis axis) was conducted at Pench Tiger Reserve, Madhya Pradesh from December 2008 to April 2009. The objectives of the study were to examine the determinants of individual and group vigilance in chital; and also to examine the t effect of conspecific behaviour on individual vigilance. I used scan sampling with fixed interval recording to estimate group vigilance and focal animal sampling with continuous recording to estimate individual vigilance levels. Three main factors that are known to affect :, vigilance from studies on other herbivores were examined: group size, density of animals in the group and visibility. Scanning behaviour was used as an estimate of vigilance. 'Scanning' refers to the state when the animal has its head above shoulder level and the senses of sight, smell and hearing are actively 'scanning' the environment. Individual vigilance was found to decrease with increasing group size, decreasing density and increasing visibility. In large groups adult males, fawns and adult females with fawns were found to be significantly more vigilant than females without fawns and yearling males. Group vigilance level was found to increase significantly with increasing group size, even as the group scan level decreased. Individuals seemed to reduce vigilance with relation to group size rather than the group vigilance level. The results suggest that individual chital do not adopt levels of scanning that maximize cooperative predator detection. The benefits of the group size effect vary with age-sex classes and other probable internal and external predation risk Factors and so vigilance is more likely governed by a combination of dilution and detection hypotheses mechanisms, the focus changing from one to the other with individual risk.