Local extinctions exceed colonization rates in a bird community during dry years in the Brazilian Caatinga

Abstract

Droughts typically result in a widespread decline in many vertebrate populations and even the local extinction of some species. However, different species vary considerably in their resistance to the effects of drought. This study aimed to estimate the relative species richness and the colonization and extinction rates in a bird community during an acute drought event in the Brazilian Caatinga. We mist-netted birds during 3 years throughout seven field seasons in two sampling plots to estimate community parameters using multi-season dynamic occupancy models. The relative richness to the regional species pool varied considerably during the study period (16–49%) with markedly low values in the severe onset of the drought. The estimates in the savanna were higher than those in the shrubby-woodland plot (~ 42 vs ~ 31 species, respectively). Pollinators and seed dispersers were characterized by median to high colonization (30–69%) and local extinction rates (37–69%), indicating low site fidelity. By contrast, granivores and insectivores made up the resident component of the community, with low local extinction and colonization rates (< 30%). Our results indicate that the diversity of Caatinga bird assemblages may decline markedly during severe droughts, primarily as a result of the displacement of species that exploit resources whose availability decreases drastically in abnormally dry years. Considering the climate scenarios predicted for tropical arid and semiarid regions worldwide, we believe that pollinators and seed dispersers will be especially vulnerable to population decline and local extinctions, which will alter community structure and the persistence of ecosystem services.