A MIGRATORY BOTTLENECK FOR THE WHITE-THROATED HAWK BUTEO ALBIGULA IN THE ANDEAN FOOTHILLS OF CENTRAL CHILE

Abstract

The White-throated Hawk Buteo albigula is one of the most abundant migratory raptors in the Austral-Neotropical system, but no bottlenecks in its migratory routes are known. Here, we describe the finding of the first migratory bottleneck for this species on the Andean slopes of central Chile. We counted a total of 5,424 White-throated Hawks migrating from south to north from 17 March until 13 April 2023, in Cachapoal, O'Higgins Region, Chile (34° S; 70° W). In addition, we counted 1,314 Variable Hawks Geranoaetus polyosoma and seven Cinereous Harriers Circus cinereus migrating through this site for a total of 6,745 raptors, which represent the largest count of migrant raptors in the Austral-Neotropical system. Both, the passage rate (24.2 hawks/hour) and the total number of White-throated Hawks observed per season, were higher at Cachapoal than at any other previous count site (daily passage rate range = 1.0–7.2 hawks/hour; total hawks per season = 35–294). We estimated that over 84% of the breeding population of White-throated Hawks transit the Cachapoal bottleneck during their autumn migration. Remote tracking technologies and observations at other points of the Andes should help to further examine this proposal. Continuing with the long-term count of White-throated Hawks in this bottleneck will allow us to assess the population trends of this important predator in the southern temperate forests.