Abstract:
Intense heat waves are occurring more frequently, with concomitant increases in the risk of catastrophic avian mortality events
via lethal dehydration or hyperthermia. We quantified the risks of lethal hyperthermia and dehydration for 10 Australian aridzone avifauna species during the 21st century, by synthesizing thermal physiology data on evaporative water losses and heat
tolerance limits. We evaluated risks of lethal hyperthermia or exceedance of dehydration tolerance limits in the absence of
drinking during the hottest part of the day under recent climatic conditions, compared to those predicted for the end of this
century across Australia. Increases in mortality risk via lethal dehydration and hyperthermia vary among the species modelled
here but will generally increase greatly, particularly in smaller species (∼10–42 g) and those inhabiting the far western parts
of the continent. By 2100 CE, zebra finches’ potential exposure to acute lethal dehydration risk will reach ∼ 100 d y−1 in
the far northwest of Australia and will exceed 20 d y−1 over > 50% of this species’ current range. Risks of dehydration and
hyperthermia will remain much lower for large non-passerines such as crested pigeons. Risks of lethal hyperthermia will
also increase substantially for smaller species, particularly if they are forced to visit exposed water sources at very high air
temperatures to avoid dehydration. An analysis of atlas data for zebra finches suggests that population declines associated
with very hot conditions are already occurring in the hottest areas. Our findings suggest that the likelihood of persistence
within current species ranges, and the potential for range shifts, will become increasingly constrained by temperature and
access to drinking water. Our model adds to an increasing body of literature suggesting that arid environments globally will
experience considerable losses of avifauna and biodiversity under unmitigated climate change scenarios.
