Abstract:
Extreme high environmental temperatures produce a variety of
consequences for wildlife, including mass die-offs. Heat waves are
increasing in frequency, intensity, and extent, and are projected to
increase further under climate change. However, the spatial and
temporal dynamics of die-off risk are poorly understood. Here, we
examine the effects of heat waves on evaporative water loss (EWL)
and survival in five desert passerine birds across the southwestern
United States using a combination of physiological data, mechanistically
informed models, and hourly geospatial temperature data. We
ask how rates of EWL vary with temperature across species; how
frequently, over what areas, and how rapidly lethal dehydration
occurs; how EWL and die-off risk vary with body mass; and how dieoff
risk is affected by climate warming. We find that smaller-bodied
passerines are subject to higher rates of mass-specific EWL than
larger-bodied counterparts and thus encounter potentially lethal
conditions much more frequently, over shorter daily intervals, and
over larger geographic areas. Warming by 4 °C greatly expands the
extent, frequency, and intensity of dehydration risk, and introduces
new threats for larger passerine birds, particularly those with limited
geographic ranges. Our models reveal that increasing air temperatures
and heat wave occurrence will potentially have important impacts
on the water balance, daily activity, and geographic distribution
of arid-zone birds. Impacts may be exacerbated by chronic effects and
interactions with other environmental changes. This work underscores
the importance of acute risks of high temperatures, particularly
for small-bodied species, and suggests conservation of thermal refugia
and water sources.
