A trait-based assessment of southern African arid-zone birds' vulnerability to climate change

Trait-based assessments allow rapid evaluation of species' vulnerability to climate change, but often overlook subtle yet consequential interspecific variation in behavioural and physiological traits. We assessed 241 southern African arid-zone bird species' vulnerability to increasing air temperature associated with climate change. Species' sensitivity was scored using organismal traits (three morphological, 25 ecological, four behavioural, three physiological). We assessed sensitivity under different trait weightings and data availability scenarios to account for data gaps and uncertainty in traits' relative importance. Relative vulnerability was assigned by combining sensitivity and exposure scores. Between 7 % and 17 % of species assessed are highly vulnerable. Passeriformes emerged as the most vulnerable order, relative to other orders assessed, on account of modest heat tolerance limits and reliance on panting, a relatively inefficient avenue of evaporative heat dissipation. Bucerotiformes, Charadriiformes, Accipitriformes and Falconiformes are also highly vulnerable. Caprimulgiformes, Columbiformes, and Strigiformes are least vulnerable, on account of pronounced evaporative cooling capacities and high heat tolerance limits. Vulnerability of Galliformes, Apodiformes and Otidiformes was inconsistent, varying substantially with trait weightings and scenarios, making them priority taxa for research and conservation. Whereas the method tends to inflate sensitivity scores for species with little available data and despite weighting uncertainty, we were able to identify taxa that consistently scored as highly vulnerable and require close attention, based on current knowledge of determinants of climate change sensitivity. Similar trait-based assessments may prove critical for ensuring population declines in unexpectedly vulnerable, or typically overlooked, species do not go unnoticed and appropriate conservation efforts are initiated.