The Vocal Repertoire of the White-throated Magpie-jay, Calocitta formosa
From February 2003 through May 2005, I studied the vocalizations and communication system of the white-throated magpie-jay (Calocitta formosa) in Santa Rosa National Park, Area de Conservacion Guancaste, Guanacaste, Costa Rica. The goal of the study was to determine the size and function of the vocal repertoire of this species. I surveyed the repertoire as a whole, and used playback and observation to study three specific call types to determine their explicit function. White-throated magpie-jays mob in response to low and high threat predators. Mobbing calls vary structurally and in delivery depending on the threat of the predator, with higher threat contexts elicit faster calling bouts and shorter calls. A playback showed that receivers pay attention to both variables, approaching if calls are short or given rapidly. Female magpie-jays beg loudly early in the nest cycle, when they are fertile. Group members provision the female at low rates initially, but increase provisioning when eggs hatch. Provisioning is positively related to begging. Begging is the loudest signal in the vocal repertoire, and is variable in structure. Begging probably indicates the need of a female, but the structural and amplitude characteristics suggest that females have co-opted begging to signal their fertility. Magpie-jays produce a distinct visual and vocal display in response to low-threat predators, the predator approach display. 134 call types were recorded during predator approaches, and the same call types were recorded in the hour before dawn. Production of and response to these calls is strongly male-biased, and males were more likely to respond to playback when their mate was fertile. These loud calls may function as alarms, but the male bias and elaborate nature suggest males have co-opted them for self-advertisement. Magpie-jays use fourteen functionally distinct call types, but use at least 150 structurally distinct types. Fourteen functional call types is not usual for a corvid, but such structural diversity is unprecedented in this group. Comparisons among nine corvids suggest that several aspects of social ecology can affect repertoire sizes.
corvid; animal communication; begging; dual-function signal; mobbing; advertisement
dissertation or thesis