When birds go bad: circumstantial evidence for infanticide in the communal South-American Guira Cuckoo

Abstract

The Guira Cuckoo (Guira guira) is a communal breeder (joint-nester) that experiences high rates of egg loss due to tossing behaviour of individuals in the group, as well as exceptionally high mortality among nestlings. Here, we report events leading to the complete loss of broods in nine nests, resulting in the death of 48 nestlings. Circumstantial evidence surrounding each episode is suggestive of infanticidal behaviour by adult group members. No evidence of predation was noted, and the occurrence of dead nestlings in the nest, or on the ground, suggests that group members may adopt infanticide as a reproductive tactic. Many groups renest at least twice during the extended rainy season, with renestings observed 18 times during 68 group-years. Hence, individuals may have repeated opportunities for breeding successfully. We predict that infanticidal behaviour should be executed by those individuals excluded from reproduction within their groups. A new nesting episode, initiated within a shorter time interval, would presumably benefit the excluded individual(s) by providing a new breeding opportunity. Direct evidence is needed to verify the infanticide hypothesis.