Social and Reproductive Behaviour of the Smooth-billed Ani

Abstract

Sentinel behaviour has been widely described in a variety of species. The term sentinel behaviour is typically used to describe a vigilant animal that watches over foraging conspecifics. Several studies have examined the advantages of sentinels in providing early detection of predators while increasing uninterrupted foraging opportunities. However, very little effort has been made to perform formal tests of coordination of sentinel bouts (i.e. the defining feature of sentinel behaviour). For the first portion of this thesis (Chapter II), I tested for sentinel coordination in Smooth-billed Anis. By examining differences between observed and expected proportion of time without a sentinel, and overlap between multiple sentinels, I show that Smooth-billed Anis do not possess a coordinated sentinel system and may have multiple sentinels overlapping at once. Competitive dynamics of broods have been suggested to influence how adaptive sex ratios allocation can occur across hatching order. Furthermore, the influences of maternal condition and variance in reproductive success (i.e. Trivers-Willard hypothesis) have also been argued to inform sex ratio allocation of offspring sex ratios in a variety of animals. In the latter part of my thesis (Chapter III), I report a sex ratio bias of last-hatched Smooth-billed Anis chicks and show that rainfall (a proxy for maternal condition) does not have a statistically significant influence on the sex ratio of broods. While a male bias in last hatched chicks may represent a tactic to mitigate asymmetrical sibling competition, the mechanisms and adaptive advantage of this strategy remains to be explored.