Frontiers in Ecology and Evolution (Jul 2020)
High Rates of Exposure to Simulated Winter Storm Cues Negatively Affect White-Throated Sparrow (Zonotrichia albicollis) Energy Reserves
Abstract
Birds are often able to cope with, and respond to, inclement weather with physiological and behavioral responses. As storms become more severe or frequent as a result of climate change, the adaptive coping responses of many species may be pushed beyond current tolerance limits. We investigated the effects of experimental recurrent inclement winter weather cues on body composition, glucocorticoid hormones, and behavior of white-throated sparrows (Zonotrichia albicollis). We used a hypobaric climatic wind tunnel to simulate storms by transiently decreasing barometric pressure and temperature, and measured behavioral responses, body composition, and baseline corticosterone levels in birds exposed, or not exposed (control), to different frequencies of simulated storms. In study 1, experimental birds were exposed to one storm per week over 9 weeks. In study 2, experimental birds were exposed to two storms per week over 12 weeks. Birds exposed to one simulated storm per week had higher fat and lean masses than control birds, with no differences in the amount of time groups spent feeding. This change in body composition suggests that birds were coping by increasing energy stores. In contrast, birds exposed to two simulated storms per week had lower fat masses compared to control birds, even though they spent more time feeding. Experimental birds in study 2 also had lower baseline corticosterone levels than controls. These changes suggest that the coping response observed in study 1 was not possible in study 2. These findings provide novel experimental evidence that birds detect and respond to changes in temperature and barometric pressure independent of other storm-related cues. One simulated storm per week resulted in potentially adaptive responses of increased mass. However, increasing the frequency of storm exposure to twice per week exceeded the birds’ capacity to maintain these energy reserves. These results also experimentally demonstrate that repeated exposure to inclement weather cues can directly affect birds’ energy reserves, even in the absence of a storm itself, with strong implications for survival as severe weather events continue to become more prevalent.
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