ANTI-PREDATORY RESPONSE OF NICOBAR LONG-TAILED MACAQUES TOWARDS SNAKE THREATS

Abstract

Threat sensitivity hypothesis states that prey species assess the intensity of threat(s) from predator species and respond accordingly. An underlying assumption of the hypothesis is that prey species is able to distinguish among different threat types. Studies have equivocally established the presence of sustained stress on exposure to predator or predator cues that corroborates the hypothesis. For primate models, where ‘snake detection theory’ is comprehensively supported, snakes appear to be strong stimuli. Hence, primates are expected to distinguish among commensal snake species. Also, once detected keeping track of its location is a good anti-predatory strategy against snakes. This is usually intertwined with frequent vocalisations, which might give information about location of predator to the conspecifics. Hence studying anti-predator vocalisation becomes extremely important for understanding the anti-predatory behaviour in general. Through the present study, we test a corollary of snake detection hypothesis, examining the snake distinguishing capacity of Nicobar long-tailed macaques (NLoTM). NLoTM occur in 3 islands of the Nicobar archipelago, Katchal, Little Nicobar and Great Nicobar. The archipelago also supports 26 species of snakes. Based on previous studies on the subject, snake species in Katchal are categorized into three categories, predatory, venomous and non-venomous. We prepared 3-D models of one snake species from each category alongside suitable control models. The models were then presented to NLoTM and their acoustic and behavioural responses were recorded. Lastly, to test the validity of snake models, the following measures were taken a) recorded at least one naturalistic encounter with the chosen snake species from each category and b) used road-killed specimens for presentation. The study also attempts to quantify the vocal repertoire of NLoTM. Fourteen different types of calls in various contexts and four different types of anti- predatory calls against snakes by NLoTM are quantified in this study. Results indicate that NLoTM differentiate snakes as predatory, venomous and non-venomous beings