Habitat Use and Morphology of Birds in Intact Amazonia Under Changing Climate

Neotropical forests contain the core of global avian diversity. Of these, the Amazon rainforest is the largest, but ~20% has already been lost to deforestation, inspiring research into the effects of clearing and fragmentation on forest birds. These studies have consistently shown that insectivorous birds that forage on or near the ground are the most sensitive species to forest disturbance. As a preamble to our study, we synthesized bird capture data collected over 40 years within continuous forest far from human disturbance. Remarkably, we found that terrestrial and near-ground insectivores have shown substantial abundance declines even within primary forest. The principal motivation for the research outlined herein is to understand the mechanism behind this surprising result. Several hypotheses have been proposed to explain vulnerability of insectivores to disturbance, one of which has implications for primary forest communities. This microclimate hypothesis posits that these birds require microclimate typical of forest interior and thus they avoid bright, hot, and dry conditions. With Amazonia facing climate change, forest interior conditions may be changing. In this study, I test three predictions of the microclimate hypothesis applied to continuous forest. First, I quantified the light and thermal niches of 10 species of terrestrial insectivores to determine whether they preferred dark and cool microclimate within primary forest. Second, I tracked the focal species Black-faced Antthrush (Formicarius analis) across the annual cycle to evaluate its behavioral thermoregulation during ambient extremes. Third, I assessed the morphology and climate exposure of 77 species through time to determine whether insectivores experienced corresponding decreases in body condition. The first two predictions were supported: I found that terrestrial insectivores were associated with remarkably dark and relatively cool conditions, and my model species sought shelter and stream valleys where conditions were buffered during the hot afternoons of the dry season. The third prediction was also supported: morphology of terrestrial insectivores changed over time, but this pattern was also pervasive throughout the entire community. I interpret these results as evidence that terrestrial insectivores are indeed sensitive specialists vulnerable to climate change, but other bird species may be also responding to its effects in what should be intact Amazonia