Satellite tracking reveals age and origin differences in migration ecology of two populations of Broad-winged Hawks ( <i>Buteo platypterus</i> )

Abstract

Recent conservation plans for long-distance Neotropical migrant birds have emphasized the importance of understanding the ecology and threats facing a species throughout its life cycle, including migration and overwintering periods. To better understand the ecology of Broad-winged Hawks (Buteo platypterus) during the nonbreeding period, we followed the movements of 14 hawks from 2 breeding populations during July 2014–April 2019 to their overwintering sites. Three juvenile and 8 adult female Broad-winged Hawks were satellite-tracked from Pennsylvania, USA, and 3 adults (2 females and 1 male) were tracked from Alberta, Canada. We documented pre-migratory movements (post-breeding) of 4 of the 14 individuals. Adults initiated fall migration on x̄ = 25 August ± 16.38 d and 2 of the 3 juveniles began fall migration on x̄ = 20 August ± 2 d. Adults had 1–12 (x̄ = 5.0 ± 3.5) stopovers in autumn that lasted for 1–24 d and juveniles had 2–5 (x̄ = 3.0 ± 1.7) stopovers that lasted 2–51 d. Adults from Pennsylvania spent the overwintering period in Nicaragua, Brazil, Peru, and Colombia (n = 8) whereas those from Alberta wintered in Suriname, Venezuela, and Bolivia (n = 3). The distance traveled on autumn migration was greater for Alberta birds (x̄ = 10,021 ± 866 km, n = 3) than for Pennsylvania birds (x̄ = 7,925 ± 1,631 km, n = 8). Migration distance and overwintering region varied by geographic origin with age but with some overlap between the 2 distinct geographic breeding populations. Broad-winged Hawks appear to follow a hybrid time–energy minimization strategy during fall and spring migrations with (1) energy minimization in North America, and (2) time minimization in Mexico and Central America. Stopover frequency, duration, and migration rate support this hypothesis.