Enduring the heat: the microclimate characteristics that determine site suitability for an endangered grassland bird during post-breeding

Environmental changes, including habitat loss and fragmentation in combination with climate change, have increased population reliance on protected areas (PAs) while also requiring individuals to adapt to changing local conditions or search for refugia when conditions deteriorate. Microclimate refugia within PAs may be critical for allowing species to persist when exposed to extreme thermal conditions, yet the availability of microclimate refugia and the ability of PAs to protect species from extremes has rarely been considered. We GPS-tracked 47 little bustards ( Tetrax tetrax ) in the Iberian Peninsula in 2009–2019, to understand their micro-scale climate and habitat use in the warmest period of the year, the post-breeding season. We compared post-breeding conditions at locations used in that period with those not used after breeding. We found that increasing temperature may reduce site suitability, while sites with greater microclimate refugia availability were more likely to be used by little bustards post-breeding. Although dispersed shrubs may provide micro-refugia, dense shrubby patches were avoided. While almost 63 % of the breeding locations were in PAs, only under 7 % of all post-breeding locations were within these key conservation areas, showing this species is not well protected across its life cycle. We assessed the impact of expected increasing temperatures from climate change scenarios and found that up to 15 % of currently used locations are predicted to become unsuitable, including those falling within PAs. Habitat management strategies should maintain landscapes with diverse characteristics that may provide shelter from extreme temperatures, such as scarce patches of low-density shrubs. • Protected areas are rarely used by little bustards during the summer. • Site usage increases with greater microclimate refugia availability. • Sparse shrubs may provide microclimate refugia. • Almost 15 % of currently used locations predicted unsuitable with global warming.