Global Warming Reshapes Bird Distributions and Conservation Priorities in Madagascar

Anthropogenic climate change is worsening its effects on human societies, economies, natural systems, and biological diversity through altered precipitation patterns and increased global temperatures. Tropical islands and areas with high endemism are especially vulnerable, because rising temperatures and changing rainfall are expected to make vast regions unsuitable for many of their narrow-ranged, endemic species potentially causing the disappearance of bird communities. By combining ecological niche models (ENMs) with community-ecology measures of biodiversity, we assess how the geographic distributions of Madagascar's birds may shift and how a changing climate could reshape their assemblages. We modelled the current and projected future distributions of 237 bird species using conventional ecological niche models for common species and ensembles of small models for rare species, projected under six general circulation models and two emissions scenarios across two future time periods, and linked these projections to assemblage-level measures of species richness, spatial beta-diversity, and community body mass. Our projections point to widespread habitat loss: even under the most optimistic assumptions, almost every species is expected to undergo range contraction, with the majority losing more than half of their current extent. Projected ranges contract by an average of 30.7% under SSP245 and 39.9% under SSP585 across two future time horizons (2041-2060, hereafter '2060', and 2081-2100, hereafter '2100'), with the steepest losses occurring by 2100 under SSP585. While no species is projected to loss its full range worldwide, within Madagascar total habitat loss could cause regional extirpation of 15-27 species by 2060 and 45-237 by 2100, depending on the emissions pathway. These contractions translate into species-richness declines in 62% of assemblages and biotic homogenization in 60% of them, with the heaviest losses concentrated in the central highlands and west and species gains largely confined to the eastern coast. Functional change followed a distinct trend: mean community body size is expected to rise in most assemblages (87.7%), regardless of compositional turnover or elevation. Although individual species respond differently depending on their dispersal ability, behaviour, and energetic demands, our results suggest that climate change may push Madagascar's bird communities toward species loss and biotic homogenization, while simultaneously reshaping the body-size structure of assemblages. Incorporating biodiversity projections of this kind is therefore essential to the success of long-term conservation planning and socio-environmental policy.