Steep Decline of a Winter Resident Bird Community in Puerto Rico Needs Swift Action
Population declines of Nearctic-Neotropical migratory birds may first become apparent on their wintering grounds where they spend up to nine months of their annual cycle. A long-term study by scientists at the Forest Service's International Institute of Tropical Forestry, which began in 1973 using constant-effort mist netting in dry forest in southwestern Puerto Rico, shows a collapse in both the abundance and diversity of wintering birds over the past 40 years, but especially during the past decade. Whereas the estimated abundance of all winter residents combined fluctuated around a common mean from 1990 to 2001, migrant numbers declined dramatically beginning in 2002. When a set of constant, linear trend, and piecewise regression models was compared, a negative linear decline was strongly supported, with local extirpation of the winter resident community predicted in 2025. Environmental factors play a key role in the population dynamics of Gu�nica's birds. Regional hurricanes, with their recent increase in occurrence and intensity, have devastating impacts on the entire avian community. However, understanding population regulation in long-distant migrants is difficult. If the declines on the wintering grounds shown in the study are widespread, the baseline for current research is greatly changed and the populations they may study are already much reduced.
Forest Service Partners