Impact of climate on the migration phenology of the endangered Little Bustard in Spain

The phenology of animals is closely tied to seasonal climatic patterns so, by altering temperature and precipitation regimes, climate change disrupts the phenological cycles of species. More specifically, the influence of rising temperatures on the phenology of bird migration has been long studied. Most of such studies focus on species performing long‐distance winter migration. However, much less is known about how short‐distance and partial migrants, with both winter and summer movements, respond to changes in climatic conditions. In this study, we analyse the migration phenology and strategy of the Little Bustard Tetrax tetrax , one of the most endangered farmland birds in Europe, and how it has changed over a 20‐year period in response to changes in temperature and precipitation. We used 117 annual trajectories from 63 GPS‐tagged Little Bustards between 2005 and 2024, collected across the species' distribution in Spain. These trajectories were classified as sedentary and migratory, and the latter into pre‐breeding and post‐breeding migrations. Our results revealed a trend for Little Bustards to advance both their pre‐ and post‐breeding migrations during the study period. The shift in post‐breeding migration is directly related to rising summer temperatures and declining summer rainfall, with birds departing earlier in hotter and drier conditions. The shift observed for the pre‐breeding migration is directly related to the temperature in their wintering grounds, with birds spending more time there with higher temperatures. This study underscores the sensitivity of Little Bustards to increasing temperatures during both breeding and wintering seasons and their adaptation capacity, which gives rise to their complex migration patterns.