Interspecific and Intraspecific Nest Threats to the Greater Ani (Crotophaga major), a Communally Breeding Neotropical Cuckoo

Abstract

Nest predation is the predominant cause of reproductive failure for birds; however, little is known about predation rates for tropical birds. Here we investigate the effect of nest height on the nesting success of greater anis (Crotophaga major), a Neotropical cuckoo bird, through both data collection on natural nests and a predation experiment using artificial nests. We hypothesize that anis prefer to lay their eggs in nests that are built at higher heights, and that nests built at higher heights experience lower rates of predation. However, our results demonstrate that nest height is not a significant factor in determining nesting success. In addition, our predation experiment reveals that artificial nests are a poor representation of nest predation on natural nests, since snakes, which are one of the most common ani nest predators, do not approach them. This experiment also led to the first visual documentation of intergroup conflict amongst greater anis, also known as sabotage, an unusual phenomenon where anis destroy each other’s clutches. We report three instances where anis sabotaged an artificial nest, as well as two instances where anis approached a nest but did not sabotage it. Using the three sabotage events, we are able to better characterize this previously unobserved behavior in order to conclude that both lone anis and whole breeding groups are responsible for sabotage, and that aggressor anis make numerous visits to the attacked clutch. We also suspect that this intergroup conflict is responsible for the evolution of a number of complicated greater ani behaviors, such as the construction of multiple partial nests during a breeding season and elaborate communal vocalizations.