Impacts of changing rainfall regime on the demography of tropical birds

Abstract

Increasing dry season length in central Panama reduced population growth rates and viability in nearly one-third of the 20 tropical bird species investigated. Such changes are projected to alter tropical bird community structure in protected areas. Biodiversity in tropical regions is particularly high and may be highly sensitive to climate change1,2. Unfortunately, a lack of long-term data hampers understanding of how tropical species, especially animals, may react to projected environmental changes. The amount and timing of rainfall is key to the function of tropical ecosystems and, although specific model predictions differ3,4, there is general agreement that rainfall regimes will change over large areas of the tropics5,6. Here, we estimate associations between dry season length (DSL) and the population biology of 20 bird species sampled in central Panama over a 33-year period. Longer dry seasons decreased the population growth rates and viability of nearly one-third of the species sampled. Simulations with modest increases in DSL suggest that consistently longer dry seasons will change the structure of tropical bird communities. Such change may occur even without direct loss of habitat—a finding with fundamental implications for conservation planning. Systematic changes in rainfall regime may threaten some populations and communities of tropical animals even in large tracts of protected habitat. These findings suggest the need for collaboration between climate scientists and conservation biologists to identify areas where rainfall regimes will be able to plausibly maintain wildlife populations.