Passerine phenology in the largest tropical dry forest of South America: effects of climate and resource availability

Abstract

ABSTRACTIn tropical dry areas, rainfall is predicted to be the most important climatic variable influencing bird phenology because it triggers food and foliage production. In addition, because resources are scarce, the moulting and breeding seasons are not expected to overlap. We conducted a 2-year study on the phenology of passerine birds at one site in Caatinga, South America’s largest dry forest region to: (a) evaluate the contributions of climate, foliage cover, and food abundance to the onset of the breeding and moulting seasons, (b) assess the duration of the breeding and moulting seasons, and (c) measure the frequency of the bird moult–breeding overlap. Birds can use rainfall or humidity as environmental cues to start their breeding seasons. The effects of water availability are mediated by both foliage cover and food abundance, but foliage cover is more important to the onset of the bird breeding season than food abundance. In contrast, both foliage cover and food abundance equally influence the timing of the primary moult. Because we found several cases of moult–breeding overlap, we suggest that some passerine species adapt that strategy to adjust the timing of their life history stages to the relatively short period of abundant resource availability.