Continent-wide tracking to determine migratory connectivity and tropical habitat associations of a declining aerial insectivore.

North American birds that feed on flying insects are experiencing steep population declines, particularly long-distance migratory populations in the northern breeding range. We determine, for the first time, the level of migratory connectivity across the range of a songbird using direct tracking of individuals, and test whether declining northern populations have higher exposure to agricultural landscapes at their non-breeding grounds in South America. We used light-level geolocators to track purple martins, Progne subis, originating from North American breeding populations, coast-to-coast (n = 95 individuals).

Tracking long-distance songbird migration by using geolocators.

We mapped migration routes of migratory songbirds to the Neotropics by using light-level geolocators mounted on breeding purple martins (Progne subis) and wood thrushes (Hylocichla mustelina). Wood thrushes from the same breeding population occupied winter territories within a narrow east-west band in Central America, suggesting high connectivity of breeding and wintering populations. Pace of spring migration was rapid (233 to 577 kilometers/day) except for one individual (159 kilometers/day) who took an overland route instead of crossing the Gulf of Mexico.