Warming in the land of the midnight sun: breeding birds may suffer greater heat stress at high- vs low-Arctic sites

Background/Question/Methods

Rising global temperatures are expected to increase reproductive costs for wildlife as greater thermoregulatory demands interfere with reproductive activities. However, predicting the environmental temperatures at which reproductive performance will be negatively impacted remains a significant hurdle. Using a thermoregulatory polygon approach, we derived a reproductive threshold temperature for an Arctic songbird the snow bunting (Plectrophenax nivalis). We defined this threshold as the temperature at which individuals must reduce activity to suboptimal levels (i.e., < 4-times basal metabolic rate) to sustain nestling provisioning and avoid overheating. We then compared this threshold to operative temperatures recorded at high (82°N) and low (64°N) Arctic breeding sites to estimate how heat constraints translate into site-specific impacts on sustained activity level.

Results/Conclusions

The thermal polygon model predicts that buntings will become behaviourally constrained at operative temperatures above 11.7°C, whereupon they must make behavioural adjustments such as reducing provisioning rates to avoid overheating. Low Arctic sites had larger fluctuations in solar radiation, consistently producing daily periods when operative temperatures exceeded 11.7°C. However, whereas the low latitude site showed predictable periods of the day where activity would need to be reduced, the model revealed that birds at the high-latitude site would face entire, consecutive days when parents would be unable to sustain required provisioning rates. These data indicate that Arctic warming is likely already disrupting the breeding performance of cold-specialist birds, but further suggests counterintuitive and severe negative impacts of warming at higher-latitude breeding locations.