Mapping evaporative water loss in desert passerines reveals an expanding threat of lethal dehydration

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.avian ecology | physiological ecology | climate change | heat waves | water balance E xtreme weather events are increasingly seen as an important factor in ecology and conservation, with consequential effects on individuals, populations, communities, and ecosystems (1-3). Recent data indicate an increase in the incidence of heat waves and extreme high temperatures (4, 5). Despite difficulties in quantifying trends in mass mortality events, heat waves are known to have caused a number of large-scale die-offs among birds, pteropodid bats, and other taxa in recent years (6, 7). Moreover, current (8) and projected (9) increases in the frequency, duration, and severity of heat waves are likely to make these mortality events more common as the century progresses (10).Birds may be particularly susceptible to heat waves given their typically diurnal activity periods, small size, and high mass-specific rates of metabolism and water loss. Small birds also have a very limited capacity to store vital resources such as water, and consequently must balance their water budgets over time scales of minutes to hours during hot weather (10). Constraints on water availability and heat stress are known to produce changes in behavior, reproductive success, occupancy, and mortality in birds (11). Heat-related mortali...

Ecological genomics predicts climate vulnerability in an endangered southwestern songbird

“…Recent work on birds supports the idea that exposure to high temperatures can result in dehydration and heat stress related mortality (Albright et al . ; Zhang et al . ).…”

“…These results are consistent with the recent work by Albright et al . () who found that small passerines in the Desert Southwest were particularly prone to mortality resulting from the failure to maintain body temperatures below lethal limits. While more research is needed, it is possible that physiological pathways responsible for overheating are related to those involved in interspecific adaptation to temperature extremes.…”

“…Recent work suggests that small desert passerines, in particular, will experience higher rates of mortality due to dehydration and hyperthermia as the frequency of extreme temperature events increases (Albright et al . ). In addition, work in poultry has shown that high temperatures can cause heart strain, or in some cases heart failure, as birds attempt to dissipate heat through increased blood circulation.…”

Revisiting concepts of thermal physiology: Predicting responses of mammals to climate change

“…The power of evaporative cooling to dissipate heat from the body, in environments in which evaporation can occur freely, probably is limited only by the capacity to consume water to replace that lost (Van Sant, Oufiero, Muñoz‐Garcia, Hammond, & Williams, ). Small endotherms are unlikely to maintain continuous evaporative cooling, because they would have to devote too much time to drinking (Albright et al., ; Crompton, Taylor, & Jagger, ). However, most large mammals do sustain some degree of continuous evaporative cooling, even in environments that would not be considered particularly hot.…”

Environmental and ecological correlates of avian field metabolic rate and water flux

“…Water relationships of birds and the factors that affect them are much less understood than the drivers of BMR and FMR. Yet, FWF is a key characteristic affecting the ability of birds to respond to climate change in arid environments (Albright et al, ; Riddell, Iknayan, Wolf, Sinervo, & Beissinger, ). Our results represent a comprehensive analysis of the environmental factors affecting interspecific variation of FWF in birds.…”