What do 35 years of sampling tell us about the population biology of tropical birds?

Tropical birds are notably diverse but more may be known about their evolutionary histories than theecology of extant populations. Basic questions persist about the magnitude and causes of variation in local abundances, the importance of density-dependent regulation and interspecific competition, and the influence of abiotic factors on quantities such as population growth rates. We report on a 35-year mark-recapture study of understory species conducted in central Panama. Analyses to date reveal considerable variation among species -even within foraging guilds -in the magnitude and patterns of change in annual recruitment, adult survival, and population growth rates. Populations of certain species are relatively constant over time (as is often assumed for tropical species) whereas others are quite dynamic. Abiotic factors such as the intensity and duration of seasonal drought appear to affect population growth rates of several species and this has important implications for predicting the effects of climate change on tropical wildlife. Integrating results of long-term studies from different regions is needed to develop even basic understanding about the “hows and whys” of dynamics in tropical bird populations.