The benefits of being smaller: Consistent pattern for climate-induced range shift and morphological difference of three falconiforme species

Climate exerts a dominant control over the distribution of species. Generally, species migrate to higher elevations to track thermal niches, but variations in morphological traits can result in trait-specific responses to climate change. Here we attempted to explore how three sympatrically distributed raptor species (the Upland Buzzard Buteo hemilasius, UB; the Common Kestrel, also called Eurasian Kestrel Falco tinnunculus, EK; and the Saker Falcon Falco cherrug, SF) would respond to climate change over time, and whether their responses would bias by different morphology. We tested the alternative hypotheses for Allen's rule for UB, EK, and SF in Qinghai Province, China, by modeling their current and future habitat suitability and confirming whether a consistent pattern exists between climate-induced range shifts and morphological differences among species. The extent of the projected distribution range within protected areas was also calculated for each species. We identified the future downward elevation shift for all the species, but with the notable northeastward shifting of the suitable climate space for UB and SF. Climate change would induce range contraction in the future, and the most acute influence is always the result of the pessimistic SSP585 scenario. No obvious pattern in climate-induced range shift was found for EK, for whom the morphological traits were significantly smaller all the time. More seriously, the ratios of highly suitable habitats being protected for our three raptor species were almost at a deficient level (below 1%). This study firstly tested the alternative hypothesis of Allen's rule among raptors in Qinghai Province unprecedently, confirmed the morphological basis for different responses to changing climate across species, and demonstrated the protection deficiency under the current protected area design. We advocate more related studies in the future to verify our findings across more taxa.