Cooperative Breeding Under Climatic Variability: population-level impacts of skipping breeding in the Greater Ani (Crotophaga major), a neotropical long-lived cuckoo

Abstract

Global climate change is predicted to alter environmental conditions across the tropics, lengthening dry seasons, raising temperatures, and increasing the frequency of severe El Niño events. As an estimated 70% of the world’s bird species depend on the tropics for reproduction, understanding how these changes are likely to affect avian reproductive success is of vital conservation importance. However, the pathways by which environmental variation might influence the nesting success of tropical birds are largely unknown. In this study, we use information-theoretic modeling approaches to investigate the effects of climatic variation on reproductive investment and success in a genotyped population of greater anis (Crotophaga major), a long-lived communally breeding cuckoo in Panama, across 11 years of monitoring. Annual reproductive output of the population varied greatly, largely driven by many ani groups skipping breeding in certain years. Likelihood of laying was strongly negatively correlated with the frequency of extreme high temperatures and with the El Niño phase of the El Niño Southern Oscillation (ENSO), which potentially reduce food availability. However, El Niño events and accompanying long dry seasons also reduced the per-capita fitness of groups that did attempt to breed, especially for birds in three-pair groups. While the mechanisms underlying these results remain equivocal, tradeoffs in reproductive advantage under different conditions may stabilize the persistence of multiple cooperative phenotypes in the greater ani. Additionally, the large variance in predation risk that could not be explained by any of our candidate predictors highlights the urgency of basic ecological research on neotropical snakes, which are the single most important regulators of reproductive success for tropical birds. In conjunction with other studies that have found that altered climate regimes depress breeding effort, our results suggest that unless tropical birds can adapt to a shifting environmental status quo, individual reproductive decision-making could have substantial population-level consequences as adverse years become more frequent.