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Environmental temperature shapes heart size evolution in birds

Fan, Haiying1; Luo, Haokang1; Chen, Guanghong1; Xie, Shiyan1; Huang, Zuhao1; Guo, Weibin1; Ke, Dianhua1

Published May 19, 2026 on Dryad. https://doi.org/10.5061/dryad.xgxd254wv

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Abstract

Hesse’s rule posits that animals living in cold environments have larger heart size compared to closely related species inhabiting warmer regions. However, evidence for this pattern in birds remains limited, and a comprehensive cross-species examination is still lacking. In this study, we tested Hesse’s rule and its modulation by biological and ecological factors using a Bayesian phylogenetic generalized linear mixed model across 915 bird species. Our results support Hesse’s rule: species in colder climates have larger hearts (after controlling for body mass) than their relatives in warmer areas. Additionally, we found that body size, flight mode, migratory behavior, and territoriality significantly influence the relationship between heart size and environmental temperature. These findings collectively demonstrate that the evolution of heart size is not governed by a singular environmental driver but is shaped by a complex interplay of selective pressures, including thermoregulatory demands, locomotor strategies, and behavioral adaptations. Future studies should aim to uncover the physiological mechanisms behind these effects and assess their generality across wider ecosystems and taxa, thereby advancing our understanding of how climate influences physiological traits and evolutionary pathways.