The Rain Never Bothered Me Anyway: Precipitation as a Predictor of Egg Laying Initiation in a Cooperative Breeder

Abstract

Photoperiod, temperature and rainfall are the three primary environmental triggers for avian breeding activity. For temperate and desert species, temperature and rainfall serve as short-term cues, with extreme temperatures inhibiting breeding and rainfall stimulating it. Such effects have not been studied to nearly the same degree in tropical species, which inhabit entirely disparate regions with relatively steady temperatures and variable, though predictable, precipitation. It is integral that research be conducted on these species, as well, so that as climate change worsens and extreme climatic events become increasingly common, we have a baseline understanding of how typical environmental shifts impact tropical avian behavior and biology. This thesis serves as a contribution to such literature as an analysis of the breeding strategies of the greater ani (Crotophaga major), a socially monogamous, Neotropical, cooperative breeder. Here, I examine the effects of precipitation on the ani's timing of egg laying, particularly for nests with two and three breeding pairs. Ultimately, I find that while annual rainfall results in earlier egg laying initiation for groups of two pairs, it delays breeding for groups of three pairs, as does breeding season rainfall. Laying times of two-pair groups are not impacted by breeding season precipitation. These trends could be due to a combination of precipitation affecting food availability, predator presence, and competition between individuals.