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Heat tolerances of temperate and tropical birds and their implications for susceptibility to climate warming
Author(s) -
Pollock Henry S.,
Brawn Jeffrey D.,
Cheviron Zachary A.
Publication year - 2021
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/1365-2435.13693
Subject(s) - ectotherm , temperate climate , biology , global warming , tropical climate , tropics , climate change , ecology , atmospheric sciences , adaptation (eye) , geology , neuroscience
Abstract Characterizing heat tolerance is critical for predicting an organism's vulnerability to climate warming. Recent studies of ectotherms report that impacts of climate warming are expected to be greater in the tropics, where ectotherms tend to have lower heat tolerances and experience air temperatures closer to their heat tolerance limits than their temperate counterparts. However, similar comparisons of heat tolerance are largely lacking for endotherms, and it remains an open question whether climate warming will also disproportionately affect tropical endotherms. To address this empirical gap, we measured thermoregulatory responses to acute heat stress in 81 bird species (23 temperate, 58 tropical), assembling the largest comparative dataset of endothermic heat tolerances to date. After controlling for body mass and experimental chamber humidity, temperate species had significantly higher heat tolerance limits (ΔHTL = 2.2°C; 45.2 vs. 43.0°C) and upper critical temperatures (ΔUCT = 1.1°C; 38.7 vs. 37.6°C) on average than tropical species. Importantly, however, these differences do not appear to impact vulnerability to climate warming, as neither thermal safety margins [i.e. the difference between upper critical temperature (UCT) and maximum air temperature, T max ] nor warming tolerances [the difference between heat tolerance limit (HTL) and T max ] differed between temperate and tropical species. We also observed substantial variation in heat tolerance among avian orders, with pigeons and doves (Columbiformes) being among the most heat tolerant species in our dataset. Overall, our results suggest that, from a physiological standpoint, tropical birds may not be systematically more susceptible to climate warming than temperate birds, contrasting previous studies of ectotherms. Furthermore, we show that certain avian clades may be more resilient to warming irrespective of local climate. However, because we only sampled at one temperate and one tropical site, we caution that replication from other habitats and localities are needed to evaluate the generality of our findings. A free Plain Language Summary can be found within the Supporting Information of this article.