Analyses of sex and individual differences in vocalizations of Australasian gannets using a dynamic time warping algorithm

Abstract

The study of the evolution of sexual differences in behavioral and morphological displays requires analyses of the extent of sexual dimorphism across various sensory modalities. In the seabird family Sulidae, boobies show dramatic sexual dimorphism in their vocalizations, and gannet calls have also been suggested to be dimorphic to human observers. This study aimed to evaluate the presence of sexually dimorphic calls in the Australasian gannet (Morus serrator) through the first comprehensive description of its vocalizations recorded at two localities; Cape Kidnappers, where individuals were banded and sexed from DNA samples, and at the Muriwai gannetry, both on the North Island of New Zealand. Calls were first inspected using basic bioacoustic features to establish a library of call element types for general reference. Extensive multivariate tests, based on a dynamic time warping algorithm, subsequently revealed that no sexual differences could be detected in Australasian gannet calls. The analyses, however, indicated extensive and consistent vocal variation between individuals, particularly so in female gannets, which may serve to signal individual identity to conspecifics. This study generates predictions to identify whether differences in Australasian gannet vocalizations play perceptual and functional roles in the breeding and social biology of this long-lived biparental seabird species.