Meeting Abstract
We studied thermoregulatory performance of summer-acclimatized wild birds to heat stress in the deserts of Australia, North America and South Africa. We measured evaporative water loss (EWL), resting metabolic rate (RMR) and body temperature (Tb) continuously using ramped temperature profiles with increasing air temperatures in 40+ species, which included 10 orders with body size ranging from 7- 450g. We estimated the heat tolerance limit (HTL) for each species by measuring Tb, EWL and RMR and activity when exposed to air temperatures ranging from 30-64°C. We found that birds from the orders Columbiformes (pigeons and doves) and Caprimulgiformes (nighthawks and nightjars) had the highest HTLs and were able to thermoregulate at air temperatures as high as 60°C. Perching birds (Passeriformes), in contrast, showed a much more limited capacity for thermoregulation at high air temperatures and exhibited HTLs near 50°C. We found that HTLs appear to be driven by the primary pathway of evaporative heat loss, where birds that evaporate water from the skin or have a well-developed gular apparatus were most effective at heat dissipation at high air temperatures. Body size was also a critical factor in determining the capacity of a species to tolerate high temperatures. This work greatly expands our knowledge of avian tolerance to heat and provides insights into how rapid warming and more intense heat waves may change avian distributions and community structure.
