Assessing the vulnerability of global dryland birds to heat waves

As global average surface temperature increases, extreme climatic events (e.g., heat waves) are becoming more frequent and intense, which can drive population responses such as rapid population declines and/or shifts in species distributions. However, extreme climatic events are largely ignored in conservation plans. Birds are very susceptible to heat waves, especially in dryland ecosystems. Understanding which birds are most vulnerable to heat waves and where these birds occur can offer a scientific basis for adaptive management and conservation. We assessed the relative vulnerability of 1,167 dryland bird species to heat waves based on a trait-based approach. 61% (715/1,167) of bird species are estimated to be vulnerable to heat waves (275 highly vulnerable, 14 extremely vulnerable). 93.4% (668/715) of bird species identified as vulnerable to heatwave impacts are currently considered non-threatened by the IUCN, which suggests that many species will likely be threatened with intensifying climate change. We identified five hotspot areas of vulnerable species, 176 vulnerable birds are distributed in Australia; 146 in Eastern Africa (Ethiopia, Somalia, Kenya); 148 in Southern Africa (Botswana, Namibia and South Africa); 81 in Central Asia (Afghanistan, Tajikistan, Turkmenistan, Uzbekistan), 71 in the southwestern United States. Populations of vulnerable species recorded in the Living Planet Database were found to be declining significantly faster than those of non-vulnerable species (p = 0.042) after heatwavesheat waves occurred. In contrast, no significant difference in population trends between vulnerable and non-vulnerable species was detected (p = 0.67) when no heatwave occurred. This suggests that our framework can correctly identify vulnerable species, and that heatwavesheat waves are already impacting the population trends of these vulnerable species. Our findings will help prioritize heatwave-vulnerable birds in dryland ecosystems in risk mitigation and adaptation management as the frequency of heat waves accelerates in the coming decades.