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Key Words
Verreaux's sifaka * Propithecus verreauxi * Ring-tailed lemur * Lemur catta * Communication * Alarm call * Madagascar
Introduction
Predation pressure is an important selective force in many animal species. In response to such pressure, prey species have evolved diverse sensory mechanisms and behavioural responses designed to increase the probability of survival [1]. Several recent studies have indicated that prey is capable of using anti-predator alarm calls given by other species living sympatrically, as well as its own species [for a review, 2]. A Malagasy prosimian, Verreaux's sifaka (Propithecus verreauxi), emits different calls in response to aerial and terrestrial predators [3, 4]. The ring-tailed lemur (Lemur catta) is another species of Malagasy prosimian, which also gives different alarm calls in response to raptors and to terrestrial predators [3, 5]. The response of semifree-ranging ring-tailed lemurs to anti-predator call playbacks suggested that these calls denote different classes of predators and functioned as referential signals [6, 7]. In southern Madagascar, these two species are sympatric and fall prey to the same carnivores (e.g. Cyptoprocta ferox) and raptors (e.g. Polyboroicks radiatus) [8]. Oda and Masataka [2] studied the responses of ring-tailed lemurs to anti-predator alarm calls given by Verreaux's sifakas in Madagascar and indicated that ring-tailed lemurs can perceive the type of predators to which the sifaka calls refer. It would also be advantageous for Verreaux's sifakas to recognize what ring-tailed lemur alarm calls denote and to respond to them. In this study, the anti-predator alarm calls of ring-tailed lemurs were played back to free-ranging Verreaux's sifakas in the Berenty Reserve, Madagascar, where sifakas and ring-tailed lemurs live sympatrically.
Methods
The subjects of this study were 4 troops of free-ranging Verreaux's sifakas in the Berenty Reserve, Madagascar. Berenty is a 200-ha forest reserve in the extreme south of Madagascar [9]. Verreaux's sifakas and ring-tailed lemurs live sympatrically in the reserve. Their daily ranging areas overlap but niches are separate [10]. Eleven animals...