Abstract
Global environmental change is leading to an increase in the frequency, intensity, and duration of extreme weather events, so effective environmental management requires an understanding not only of the physiological response of organisms to increased mean temperatures, but also to extreme environmental conditions. To determine the physiological consequences of heatwaves on energy and water balance of arid-adapted zebra finches (Taeniopygia guttata), we measured field metabolic rate and water turnover rate of wild, free-living finches during a heatwave (consecutive days of maximum ambient temperature of 40–45°C) and during a cooler period (maximum ambient temperature of 28°C) during a summer drought. To understand how birds accommodated their energy and water requirements, we also monitored feeding and drinking behavior of zebra finches at the study site on hot and cold days over 2.5 months during the same summer. Zebra finches can accommodate heatwaves without major impacts on field energy or water turnover, even when the heatwave is superimposed on high summer temperatures and long-term drought, so long as drinking water is available. In fact, cooler periods may pose a greater energetic challenge than heatwaves during drought, when food availability is limited, due to the increased thermoregulatory cost of maintaining a high body temperature against a thermal gradient. Zebra finches avoided or limited activity during the most thermally challenging periods of the day. Their pre-emptive feeding and drinking in preparation for hours of relative inactivity at high ambient temperature, together with a high body water content and reduced midday activity and metabolic heat production, enabled zebra finches to maintain body mass during a heatwave. Predicting upcoming periods of unfavorably high ambient temperature, together with a high body water content, may be essential for survival by desert birds of extreme ambient temperature during heatwaves.
Highlights
Global environmental change is impacting average climatic conditions such as mean ambient temperature and annual rainfall but is increasing the intensity, frequency, and duration of extreme weather events such as heatwaves (Meehl and Tebaldi, 2004; Tebaldi et al, 2006; Diffenbaugh and Field, 2013; IPCC, 2014)
Birds captured during hot periods had a higher body mass (12.2 ± 0.20 g, N = 20) than during cool periods (11.5 ± 0.17 g, N = 20; t38 = 2.43; p = 0.020), but body mass did not differ significantly for those 10 individuals that were recaptured during each period and for which field metabolic rate (FMR) and water turnover rate (WTR) were measured (12.1 ± 0.23 hot and 11.4 ± 0.21 cool, mean = 11.7 ± 0.17 g, N = 20; t18 = 2.09; p = 0.051)
Metabolic water production (MWP) calculated from FMR was correspondingly lower during hot (0.953 ± 0.092 ml day−1) compared to cool periods (1.317 ± 1.00 ml day−1), and was 20 ± 2.3 and 34 ± 2.6% of the birds’ WTR respectively
Summary
Global environmental change is impacting average climatic conditions such as mean ambient temperature and annual rainfall but is increasing the intensity, frequency, and duration of extreme weather events such as heatwaves (Meehl and Tebaldi, 2004; Tebaldi et al, 2006; Diffenbaugh and Field, 2013; IPCC, 2014). These extreme weather events may have a significant, immediate, and long-lasting impact on biodiversity, especially when combined with an underlying gradual mean change in climate (Saunders et al, 2011; Harris et al, 2018; Ruthrof et al, 2018). Our current understanding of the physiological function of most organisms is inadequate to determine effective mitigation strategies for even background climate change, and is even less able to predict and manage their response to unpredictable, extreme weather events (Chown et al, 2010; Ratnayake et al, 2019)
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