Absence of microclimate selectivity in insectivorous birds of the Neotropical forest understory

Local abiotic conditions (microclimates) vary spatially and selection of favorable microclimates within a habitat can influence an animal's energy budgets, behavior, and ultimately, fitness. Insectivorous birds that inhabit the understory of tropical forests may be especially sensitive to environmental variation and may select habitat based on microclimatic (e.g. temperature, humidity, light) conditions. Sensitivity to microclimate could contribute to the population declines of understory insectivores in response to forest fragmentation or degradation, which changes the physical structure of the forest, thereby increasing light intensity and temperature and decreasing humidity. To understand the role of microclimates in the habitat selection of understory insectivores, we characterized the microclimatic associations of nine species of understory insectivores at three sites along a precipitation gradient and across seasons in central Panama. We compared the distributions of microclimates selected by birds with microclimates at randomly chosen points within their home ranges to test for microclimate selectivity. We predicted that: (1) birds would select microclimates that are more humid, cooler, and less bright than random microclimates, (2) selectivity would be greater in hotter, drier habitats and (3) selectivity would be greatest in the dry season. We found no evidence of selectivity for the nine species we sampled on a seasonal or spatial basis. Microclimate variation was minimal in the forest understory at all sites, particularly in the wet season. Understory insectivores did not use microhabitats characterized by high light intensity, and may be sensitive to light, though the mechanism remains unclear. The lack of microclimate variation in the understory of tropical forests may have serious fitness consequences for understory insectivores due to increasing temperatures associated with climate change coupled with a lack of thermal refugia. (C) 2014 Elsevier Ltd. All rights reserved.