Bats in the megafire: assessing species' site use in a postfire landscape in the Sierra Nevada

Large high-severity fires are increasing in frequency in many parts of the world, including the coniferous forests of the Sierra Nevada mountains. These "megafires" alter vegetation and environmental conditions in forests, yet their impacts on native wildlife remain poorly understood. Bats play an important role in forest ecosystems, but their responses to megafires likewise are understudied. We investigated bat responses to the King Fire, a megafire that burned nearly 40,000 ha within the Eldorado National Forest in 2014, half of it at high severity. From June to September 2017, we used remote acoustic recorders to survey bats at 26 sites with varying fire severity (unburned, mixed, and high severity). We analyzed data with Royle-Nichols occupancy models to investigate how bat space use was influenced by megafires, and whether this response was driven by prey availability, fire severity, or fire-altered habitat conditions. We calculated prey species richness, biomass, and abundance, from moths sampled with blacklight surveys. Vegetation covariates included tree density, canopy cover, and shrub density, measured along vegetation transects. To capture general effects of fire, we also included fire severity and the percentage of dead trees as potential covariates on space use. Prey variables were highest in unburned forests, were the most common predictors of, and generally had positive effects on bat space use. Responses to tree density and canopy cover varied by species; the most common vegetation covariate, shrub density, had weak positive effects on bat space use. In spite of the varying prey and vegetation conditions across fire severity categories, most bats showed weak to no response in space use to fire severity and tree mortality. We attribute this to the highly mobile nature of bats, which reduces the impact of potentially negative local conditions.