Microclimate refugia shape microclimatic niches and predict individual variability in post-breeding migration in a partially migratory species.

The characterization of species' environmental niches can help predict biodiversity responses to global environmental change and identify areas where environmental suitability declines as the conditions change. However, environmental niches, that is the full range of conditions a species experiences, are frequently described at coarse spatial and temporal scales, thus are unlikely to capture the across-individual variability in exposure to microclimate conditions. Within species ranges and even within populations, individuals may vary in their ability to access microclimate refugia or may adopt different movement strategies to avoid exposure to unsuitable conditions. This individual variability currently remains unclear but could help us understand species' capacity to adjust to changes in climate. We used an 11-year satellite tracking dataset and high-resolution remotely sensed habitat and climate information to investigate the microclimatic niche of a partially migratory grassland bird, the endangered little bustard (Tetrax tetrax) in the species' western stronghold populations in Southern Europe. Our study, including both breeding and post-breeding seasons, aimed to determine whether the local conditions experienced by individuals during the breeding season can be used to predict individual movement strategies after breeding. Furthermore, we examined whether the distance travelled during post-breeding dispersive migration influenced the level of dissimilarity between seasonal niches experienced by individuals. The little bustard microclimatic niche was characterized along a gradient of temperature and microclimate refugia availability. Our results revealed that individuals occupying breeding areas with low microclimate refugia availability were more likely to move longer distances after breeding. Furthermore, long-distance migratory individuals maintained similar microclimatic niches across seasons, whereas short-distance migrants predominantly displayed a higher niche dissimilarity between seasons. Temperature and microclimate refugia availability during the breeding season can help predict individual differences in migratory behaviour of little bustards and their niche dissimilarity across seasons. Global warming and subsequent declines in microclimate refugia availability may force this species to move earlier and travel longer distances after breeding. This study provides information that can help design conservation strategies for little bustards and other endangered grassland bird species exposed to high temperatures.