Natal dispersal and philopatry of chimango caracaras (Milvago chimango) in suburban, rural and natural habitats, determined by band recovery and re-sighting data

Abstract

Natal dispersal is a process whereby birds move from their birthplace to the site of their first attempt at reproduction. This process has strong implications for the dynamics and genetic structure of populations. However, studies on the dispersal of neotropical birds of prey are scarce. Here we investigated the post-fledgling and natal dispersal and philopatry of a common but poorly studied raptor, the Chimango Caracara (Milvago chimango) through band recovery and resighting data analysis across human modified and natural environments. During 10 years of study we banded 1738 individuals, with 793 banded as nestlings or fledglings in suburban, rural and natural habitats of central Argentina. We determined the dispersal distance for 94 individuals, 80 of which were recaptured at their natal site. Nine individuals moved between 5 and 120 km during the post-fledgling period (i.e. prior to their first breeding attempt) and five had natal dispersal distances (i.e. from natal to definitive breeding sites as adults) that varied between 10 and 800 km. Throughout band re-sighting we determined that Chimango Caracaras were able to breed at an age of 2 years old. Individuals tended to disperse to similar colonies and habitats as their natal sites (i.e. similar type of colony and degree of anthropogenic disturbance). Although most Chimango Caracaras exhibited short-distance dispersal (<10 km), some individuals may disperse over large distances (≈ 800 km). Our study shows for the first time the impact of natal area on breeding grounds in Chimango Caracara with consequent predictions for population structuring of this species.