A migratory bird that gets stuck with second-rate winter accomodations will achieve only lackluster breeding success the next summer, hundreds or even thousands of miles away, a new study suggests.
Isotopes are forms of atoms with different numbers of neutrons.
Birds that arrive late, however, show ratios typical of poor, dry habitats. Monitoring redstarts wintering in Jamaica, the researchers found that dominant males and the tougher females claim forest territories with abundant insects for food. An underclass of smaller, weaker redstarts gets pushed into scrub, which has fewer insects. The researchers found that birds in prime winter territories increased or maintained their weight, but the birds in the slums lost up to 11 percent of their fat for the flight north, leaving some 10 days later than birds in the forest. The researchers could not track those particular birds north, a problem with many such studies.