An Avian Enigma: Decoding Hummingbird Vocalizations in Courtship and Territoriality

Abstract

Many animals use acoustic signaling to mediate social interactions such as competition, courtship, and territory defense. Birds, with their diverse vocal repertoires, present an optimal study system to examine these signals. In this thesis, I focused on the chip call of the broad-tailed hummingbird (Selasphorus platycercus), a migratory species that stands out for its evolutionary loss of song. While the chip call has been observed in several species of hummingbirds, the structure of this monosyllabic vocalization across behavioral contexts is largely unknown. By collecting field recordings and running acoustic playbacks of the broad-tailed hummingbird chip call, I investigated the acoustic features and syntax of male and female chip calls to better understand their roles in courtship and territoriality. I found that male and female calls exhibit vocal sexual dimorphism in chip call maximum frequency, minimum frequency, and duration. I also identified a bimodal distribution in within-bout call interval consistent in both males and females and more prominent in territorial pursuit, vigilance, and courtship contexts. A closer examination of syntactic structure using Markov analysis revealed a bias toward highly stereotyped, fast, successive chip calls during male pursuit and vigilance. No such pattern was found in rufous hummingbirds. These results suggest that broad-tailed hummingbirds encode sex-specific and context-specific information in the acoustic structure of their chip calls in lieu of more complex song. This study highlights the importance of the acoustic landscape to animal communication and paves the way for future studies examining call patterning within and across hummingbird species.