The ecstatic display call of the Adélie penguin (Pygoscelis adeliae)

Abstract

The ability to understand the complex mechanisms by which species communicate has been the focus of study for many years. The Adélie penguin (Pygoscelis adeliae) breeds in vocally challenging Antarctic colonies and has evolved a complex system of intra- and intersexual visual and vocal behaviours. Unique to the Adélie penguin, is the presence of two distinct display calls, the Loud Mutual Display (LMD) call and male Ecstatic Display Call (EDC). The EDC is used for both mate choice and territory defence; but apart from general structure and function this call remains basically unstudied. Therefore, the aim of this study is to examine the EDC with regard to its function (during mate choice) and variability over time, with location and with changing conditions. It is predicted that the EDC will be an individual call that is distinct from the LMD call. Additionally, the effects of an inclement breeding season on factors that affect breeding success will be examined using a logistic regression approach. The study took place over two breeding seasons(2000/1 & 2002/3) on Ross Island, Antarctica, with the majority of research being conducted at Cape Bird. Results of the study indicate that the EDC is an individual call that cannot reliably be described as a male display as females also give an EDC that is acoustically comparable. The similarities between the EDC and the LMD call seem to relate only to syllabic organisation (structure), as almost every call parameter was different between call types. Furthermore, several call parameters differed between Ross Island colonies. These parameters varied with both geographical location and colony size. In conjunction with variation in call parameters, the health and breeding success of the colonies was different. The stability of call parameters (from Cape Bird) indicated that parameters that separate colonies not only alter between breeding years, but also vary during a single breeding season. The function of the EDC as an honest signal during mate choice was supported by spectral analyses. These analyses found heavier males had significantly lower Frequency Modulation (FM) in the short repeated syllables of their calls than lighter males. Furthermore, a male’s breeding success could be predicted during the early breeding season by the FM. Logistic regression models showed that early male arrival, weight and good nest quality were most influential in predicting fledging success. The logistic regression method also showed that the parameters measured varied in their predictive ability as the season progressed. This study has not only enhanced the wealth of knowledge regarding Adélie breeding behaviour and developed our understanding of the vocal repertoire of this species, but also has implications for honest signalling theory, and the evolution and stability of vocal variation at different spatial and temporal scales.