Light and thermal niches of ground-foraging Amazonian insectivorous birds

Insectivores of the tropical rainforest floor are consistently among the most vulnerable birds to forest clearing and fragmentation. Several hypotheses attempt to explain this pattern, including sensitivity to extreme microclimates found near forest borders—particularly brighter and warmer conditions. Importantly, this “microclimate hypothesis” has additional implications for intact forest under global climate change that could be evaluated through direct assessment of the light and temperature environment of terrestrial insectivores. In this study, we harness novel technology to directly quantify the light and thermal niches of 10 species of terrestrial insectivores in undisturbed Amazonian rainforest. Loggers placed on birds (N = 33) and their environment (N = 9) recorded nearly continuous microclimate data from 2017–2019, amassing >5 million measurements. We found that midday light intensity in treefall gaps (~39,000 lux) was >40 times higher than at the ground level of forest ...