Abstract

Sibling aggression is an agonistic behavior among chicks of the same nest that occurs soon after hatching. Despite its occurrence being well-documented in several species of raptors, information available for Neotropical species is scarce. During the breeding season of 2013–2014, we conducted behavioral observations on the nests of two pairs of the Black-chested Buzzard-Eagle (Geranoaetus melanoleucus) in central Chile. Brood sizes for these nests were two and three chicks. Around 5–7 days after hatching, the first sibling aggressions were observed in both nests. They were characterized by repetitive vigorous attacks by both, older and younger chicks. We observed this behavior until the chicks were 20–25 days old, but no brood reduction occurred. This work represents the first detailed record of sibling aggression in a diurnal raptor in Chile.