Relative species mobility is a key determinant of avian diversity in post-megafire recovery

Megafires are a class of very large wildfire linked to climate change. Such fires typically cause extensive loss of assets, and while the economic and social costs are often quantified, much less is known about the impacts on forest biota. This study investigated the effects of a megafire of unprecedented scale on birds in dry eucalypt forests of south-eastern Australia. We aimed to determine how the extent of high-severity fire influenced patterns of species occurrence and recovery of diversity post-megafire, with consideration of pre-fire occurrence and richness. Because high mobility may be an advantageous trait in fire-prone forests, relatively mobile species (migrants, nomads) and exclusively sedentary species were evaluated separately. Acoustic recorders were used to survey birds in the year before and one year after the megafire. To explore the scale at which birds may respond to high-severity fire, the proportion of area burnt at high severity was calculated in concentric circles with radii 325 and 564 m from the acoustic recorder in each site. Individual species responses were estimated using a Bayesian latent variable model. Separate Bayesian species richness models were compared based on out-of-sample predictive accuracy. Species responses to megafire and the extent of high-severity fire were mixed (positive, negative, no response), but alpha and gamma diversity were close to pre-fire levels. Negative responses to megafire shown by several species corresponded with previously published estimates of population declines. Pre-fire numbers of species in sites predicted post-fire richness, with high-severity fire having no additional influence. Relatively mobile species were prominent in the recovery of the avifauna, suggesting that dispersal capacity played an important role in recolonisation. Further studies incorporating fire, climate, environmental attributes and human land use are required to advance our mechanistic understanding of avian occurrence in fire-prone forests.