Making History

Researchers have long wondered whether migratory birds return to their birthplace to breed. But a new study, co-authored by Colin Studds, Kurt Kyser and Peter Marra at the Smithsonian Migratory Bird Center, says choice of breeding ground is affected by where young birds spend their first winter. The scientists followed the travels of the American redstart, a small songbird native to North America that winters in Latin America and the Caribbean. While some redstarts settle in Jamaica's lush mangrove swamps, others end up in nearby dry scrub, where they tend to lose weight. Come spring, healthier birds head home about a week sooner than their scrub-dwelling, less fit brethren. These early birds arrive in the southern United States when food is plentiful. The thinner redstarts leaving later must head farther north to find enough food. The research suggests that climate change could impact migratory patterns. Tropical climates are predicted to get drier, "which could delay bird departure, even from good habitats," says Marra.