Metabolic heat production and thermal conductance are mass-independent adaptations to thermal environment in birds and mammals

Trevor S. Fristoe, Joseph R. Burger, Meghan A. Balk, Imran Khaliq, Christian Hof, James H. Brown

Research output: Contribution to journalArticlepeer-review

66 Scopus citations


The extent to which different kinds of organisms have adapted to environmental temperature regimes is central to understanding how they respond to climate change. The Scholander-Irving (S-I) model of heat transfer lays the foundation for explaining how endothermic birds and mammals maintain their high, relatively constant body temperatures in the face of wide variation in environmental temperature. The S-I model shows how body temperature is regulated by balancing the rates of heat production and heat loss. Both rates scale with body size, suggesting that larger animals should be better adapted to cold environments than smaller animals, and vice versa. However, the global distributions of ∼ 9,000 species of terrestrial birds and mammals show that the entire range of body sizes occurs in nearly all climatic regimes. Using physiological and environmental temperature data for 211 bird and 178 mammal species, we test for mass-independent adaptive changes in two key parameters of the S-I model: basal metabolic rate (BMR) and thermal conductance. We derive an axis of thermal adaptation that is independent of body size, extends the S-I model, and highlights interactions among physiological and morphological traits that allow endotherms to persist in a wide range of temperatures. Our macrophysiological and macroecological analyses support our predictions that shifts in BMR and thermal conductance confer important adaptations to environmental temperature in both birds and mammals.

Original languageEnglish
Pages (from-to)15934-15939
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number52
StatePublished - Dec 29 2015

Bibliographical note

Funding Information:
We thank Felisa A. Smith and reviewers for their helpful comments. I.K. was supported by the Higher Education Commission of Pakistan and the German Academic Exchange Service. I.K. and C.H. were supported by the Landes-Offensive zur Entwicklung Wissenschaftlichökonomischer Exzellenz funding program to the Biodiversity and Climate Research Centre. J.R.B. was supported by the Shadle Fellowship from the American Society of Mammologists. M.A.B. and J.R.B. were supported by the Program in Interdisciplinary Biological and Biomedical Sciences through the University of New Mexico (Grant T32EB009414) from the National Institute of Biomedical Imaging and Bioengineering.


  • Bergmann's rule
  • Body size
  • Macrophysiology
  • Metabolic rate
  • Thermal conductance

ASJC Scopus subject areas

  • General


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