COS 73-5 - Microhabitat selection in Costa Rican birds is mediated by temperature

Abstract: Climate change is driving increasingly frequent and severe temperature extremes. At the same time, large-scale habitat conversion and degradation are eliminating the ability of organisms to cope with harsh conditions. When temperatures spike, organisms often survive by retreating to insulated tree canopies and other thermally-buffered habitats, so land-use change that removes large amounts of natural vegetation can result in exposure to lethal temperatures. As such, maintaining or restoring thermally-buffered habitats in disturbed landscapes such as agriculture could be crucial to species persistence in a changing world. However, we currently have very little information about how species use agricultural landscapes, let alone about whether particular types or amounts of habitat could provide them with refuges against climate extremes. We aimed to quantify the use of thermally-buffered habitats by birds, a taxonomic group that has experienced recent declines and is vulnerable to climate extremes. Specifically, we used ~13,500 observations of habitat selection across 80 bird species in northwest Costa Rican forests and agriculture to examine (1) how use of thermally-buffered microhabitats (i.e., the midstory or understory beneath tree canopies) changed as temperatures increased as well as how these temperature effects were modulated by (2) land cover and (3) species traits.



We found that Costa Rican birds were significantly more likely to be found beneath the canopy of rainforest trees at higher temperatures, with the probability that an individual selects for this habitat rising by 1.3% for every 1°C temperature increase. Correspondingly, birds were less likely to use tree canopies when temperatures increased (decreasing by 1% for every 1°C increase). Contrary to our initial hypotheses, we found that birds were more likely to retreat to the shade of tropical trees at higher temperatures at sites with higher forest cover (and less likely to change their habitat selection in open agricultural sites). Finally, generalist species that forage across a wider range of forest strata and diet items were more likely to exhibit temperature-mediated habitat selection compared to specialists in forest strata and diet. Together, our study suggests that while tropical trees may provide species with thermal refuges, the benefits of thermally-buffered habitats may both be species-specific and depend on the quality of vegetation present. Ensuring that working landscapes are productive and biodiverse under a changing climate might thus necessitate maintaining nearby forest patches with understory and midstory habitat under a closed canopy.