TY - JOUR
T1 - Heat tolerances of temperate and tropical birds and their implications for susceptibility to climate warming
AU - Pollock, Henry S.
AU - Brawn, Jeffrey D.
AU - Cheviron, Zachary A.
N1 - Funding Information:
We thank the Autoridad Nacional del Ambiente (ANAM) for providing research permits to work in the Republic of Panama and the Smithsonian Tropical Research Institute (STRI)—especially Raineldo Urriola, Adriana Bilgray and Owen McMillan, Egbert Leigh and Joe Wright for logistical support. We thank the South Carolina Department of Natural Resources for providing research permits to work in South Carolina and Brett DeGregorio, Chris McBride and especially Tracey Tuberville for logistical support. Access to field and laboratory facilities on the Savannah River Site were made possible by Award Number DE-FC09-07SR22506 from Department of Energy to the University of Georgia Research Foundation. All protocols were approved by the University of Illinois at Urbana-Champaign (#12202), the University of Georgia (#A2013 02-014-Y1-A0) and the Smithsonian Tropical Research Institute (#2013-0101-2016) Institutional Animal Care and Use Committees. We also thank: Blair Wolf, for helpful discussions and insightful guidance on avian thermal physiology; Mark Vukovich for generously allowing us to catch birds at his feeders; and finally, all of the field technicians who helped collect these data, including Yocelin Bello, Fernando Cediel, Noah Horsley, Sean MacDonald, Simon Nockold, Diego Rincón-Guarín, Chris Wagner, Tyler Winter and Kittie Yang. This research was supported in part by an NSF Graduate Research Fellowship, Smithsonian Tropical Research Institute Short-Term Fellowship, Smithsonian Committee for Institutional Cooperation Fellowship and University of Illinois PEEC Summer Research Grant to H.S.P.; a U.S. Army Corps of Engineers Engineer Research and Development Center - Construction Engineering Research Laboratory (ERDC-CERL) grant (#W9132T-11-2-0010) and U.S. Department of Agriculture National Institute of Food and Agriculture Grant (#875370) to J.D.B. The authors declare no competing interests.
Funding Information:
We thank the Autoridad Nacional del Ambiente (ANAM) for providing research permits to work in the Republic of Panama and the Smithsonian Tropical Research Institute (STRI)—especially Raineldo Urriola, Adriana Bilgray and Owen McMillan, Egbert Leigh and Joe Wright for logistical support. We thank the South Carolina Department of Natural Resources for providing research permits to work in South Carolina and Brett DeGregorio, Chris McBride and especially Tracey Tuberville for logistical support. Access to field and laboratory facilities on the Savannah River Site were made possible by Award Number DE‐FC09‐07SR22506 from Department of Energy to the University of Georgia Research Foundation. All protocols were approved by the University of Illinois at Urbana‐Champaign (#12202), the University of Georgia (#A2013 02‐014‐Y1‐A0) and the Smithsonian Tropical Research Institute (#2013‐0101‐2016) Institutional Animal Care and Use Committees. We also thank: Blair Wolf, for helpful discussions and insightful guidance on avian thermal physiology; Mark Vukovich for generously allowing us to catch birds at his feeders; and finally, all of the field technicians who helped collect these data, including Yocelin Bello, Fernando Cediel, Noah Horsley, Sean MacDonald, Simon Nockold, Diego Rincón‐Guarín, Chris Wagner, Tyler Winter and Kittie Yang. This research was supported in part by an NSF Graduate Research Fellowship, Smithsonian Tropical Research Institute Short‐Term Fellowship, Smithsonian Committee for Institutional Cooperation Fellowship and University of Illinois PEEC Summer Research Grant to H.S.P.; a U.S. Army Corps of Engineers Engineer Research and Development Center ‐ Construction Engineering Research Laboratory (ERDC‐CERL) grant (#W9132T‐11‐2‐0010) and U.S. Department of Agriculture National Institute of Food and Agriculture Grant (#875370) to J.D.B. The authors declare no competing interests.
Publisher Copyright:
© 2020 British Ecological Society
PY - 2021/1
Y1 - 2021/1
N2 - 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, Tmax] nor warming tolerances [the difference between heat tolerance limit (HTL) and Tmax] 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.
AB - 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, Tmax] nor warming tolerances [the difference between heat tolerance limit (HTL) and Tmax] 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.
KW - birds
KW - climate warming
KW - endotherms
KW - heat tolerance limit
KW - thermal safety margin
KW - upper critical temperature
KW - warming tolerance
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U2 - 10.1111/1365-2435.13693
DO - 10.1111/1365-2435.13693
M3 - Article
AN - SCOPUS:85092574737
VL - 35
SP - 93
EP - 104
JO - Functional Ecology
JF - Functional Ecology
SN - 0269-8463
IS - 1
ER -