Changes in thermal niche position and breadth of bird assemblages in Spain in relation to increasing temperatures

Abstract

Aim: Animal communities around the world are responding to climate change by altering their taxonomic composition, mainly through an increase in the colonisation rate of warm-dwelling species and the local extinction of cold-dwelling ones. We assessed whether the taxonomic composition of bird assemblages in peninsular Spain has changed in accordance with the recent increase in temperature. We also evaluated the role of species thermal affinities and population dynamics on these changes. Location: Peninsular Spain. Taxon: Birds. Methods: We compared assemblages reported in the last Spanish breeding bird atlases (1998–2002 vs. 2014–2018) in 10 × 10 km squares. We described species' thermal niches by overlaying global species breeding distributions and world temperature metrics (based on mean, minimum, maximum and range), and then aggregated them to obtain a set of community thermal indices for each assemblage (CTIs and CTR for ranges). Long-term average temperatures and local current temperatures were related to changes in CTIs using spatial GLMMs, which considered habitat change. We identified the species most responsible for variation in assemblages and regressed species' influence on thermal affinities and population dynamics. Results: CTIs increased with temperature and warm-dwelling species became more prevalent to the detriment of cold-dwelling ones. However, we found a counteracting effect of temperature and habitat. Cold-dwelling forest species were among the most influential species, mainly through colonisation, while warm-dwelling farmland species contributed through local extinctions (both attenuated local increases in CTI). The mean thermal breadth of assemblages (CTR) decreased with temperatures. Main conclusions: The taxonomic composition of bird assemblages shifted in line with the main expectations due to global change (thermophilisation), mainly due to local colonisation of warm-dwelling species, although it did not show the pattern of thermal homogenisation suggested elsewhere. Our results add further evidence of the interplay between climate warming and land-use change in the ongoing adjustment of animal communities.