Climate trends and behavior of a model Amazonian terrestrial insectivore, Black-faced Antthrush, indicate adjustment to hot and dry conditions

Rainforest loss threatens terrestrial insectivorous birds throughout the
world’s tropics. Recent evidence suggests these birds are declining in
undisturbed Amazonian rainforest, possibly due to climate change. Here, we
first asked whether Amazonian terrestrial insectivorous birds were exposed
to increasingly extreme ambient conditions using 38 years of climate data.
We found long-term trends in temperature and precipitation at our study
site, 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 periodic intervals
of ambient extremes and prospective microclimate refugia within
undisturbed rainforest from 2017–2019. Simultaneously, we examined how
tagged Black-faced Antthrushes (Formicarius analis) used this space. We
collected >1.3 million field measurements quantifying ambient
conditions in the forest understory, including along elevation gradients.
For 11 birds, we obtained GPS data to test whether birds adjusted their
cover usage using variation in GPS fix success (n = 2,724) as a proxy and
elevation using successful locations (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 apparently entered cover and shifted downslope. Because
climate change intensifies the hot, dry conditions that antthrushes
seemingly avoid, our results are consistent with the hypothesis that
climate change decreases habitat quality for this species. If other
terrestrial insectivores are similarly sensitive, climate-induced changes
to otherwise intact rainforest may be related to their recent declines.