ACOUSTIC COMMUNICATION IN THE JOINT-NESTING SMOOTH-BILLED ANI, CROTOPHAGA ANI

Abstract

<p>I studied acoustic and visual communication in the Smooth-billed Ani, a joint-nesting, cooperatively breeding cuckoo. I describe vocal repertoire of this species using both qualitative and quantitative methods. In this first, formal description of the species’ repertoire, I provide verbal descriptions of each call type, the contexts in which each call is produced, spectrograms, and acoustic measurements for each call type. I used multivariate statistics to show that call types can be correctly classified based on acoustic measurements alone. Smooth-billed Anis are capable of complex communication, including the use of functionally referential alarms and signals of aggression that reliably predict attack. Functionally referential signals are produced in response to a specific set of stimuli and elicit predictable, appropriate responses in signal receivers, even in the absence of any other cues. I show that anis produce two distinct signal types, <em>chlurps</em> and <em>ahnee</em> <em>alarms</em>, in response to two different predator classes, aerial and terrestrial, respectively. I also show that receiver responses to playback of these alarm signals are distinct and appropriate to evade predation from aerial and terrestrial attackers. Aggressive signals should increase in aggressive contexts, predict subsequent aggression and elicit responses from signal receivers. I show that <em>hoots</em>, an acoustic signal, and throat inflation, a visual signal, both increase in aggressive contexts and reliably predict aggressive escalation in the form of direct attacks on a mount. The receiver response to <em>hoots</em> and throat inflation remains to be tested. In the synthesis, I provide suggestions for future research.</p>