Climate trends and behavior of an avian forest specialist in central Amazonia indicate thermal stress during the dry season
AbstractRainforest loss threatens terrestrial insectivorous birds throughout the world’s tropics. Recent evidence shows these birds to be declining in undisturbed Amazonian rainforest, possibly due to climate change. Here, we first addressed whether Amazonian terrestrial insectivores were exposed to climate change using 38 years of climate data. We found that climate has changed in central Amazonia, especially in the dry season, which was ∼1.3°C hotter and 21% drier in 2019 than in 1981. Second, to test whether birds actively avoided hot and dry conditions, we used field sensors to identify ambient extremes and prospective microclimate refugia within undisturbed rainforest from 2017 – 2019. Simultaneously, we examined how tagged Black-faced Anthrushes (Formicarius analis) used this space. We collected 1.4 million field measurements quantifying ambient conditions in the forest understory, including along elevation gradients. For 11 birds, we obtained GPS locations to test whether birds adjusted their shelter use (n = 2,724) or elevation (n = 640) across seasonal and daily cycles. For four additional birds, we collected >180,000 light and temperature readings to assess exposure. Field measurements in the modern landscape revealed that temperature was higher in the dry season and highest on plateaus. Thus, low-lying areas were relatively buffered, providing microclimate refugia during hot afternoons in the dry season. At those times, birds entered shelters and shifted downslope, reducing their thermal exposure by 50%. Because climate change intensifies the hot, dry conditions that antthrushes avoid, our results are consistent with the hypothesis that climate change lowers habitat quality for terrestrial insectivores. This sensitivity may be related to their declines within ‘undisturbed’ Amazonian rainforest.
