Longer wing bones in warmer climates suggest a role of thermoregulation in bird wing evolution
Author(s)
Type
Journal Article
Abstract
Aim
The tendency for animals in warmer climates to be longer-limbed (Allen's Rule) is widely attributed to the demands of thermoregulation. The role of thermoregulation in structuring bird wings, however, has been overshadowed by the selective demands placed on wings by flight. We test whether occurrence in warmer climates is associated with longer wing bones.
Location
Global.
Time Period
Current.
Major Taxa Studied
Aves: Passeriformes.
Methods
Using computer vision, we measure wing-bone length from photographs of museum skeletal specimens for 1520 species of passerine birds. We then model the relationship between wing-bone length and temperature, accounting for allometry, the demands of flight efficiency and manoeuvrability, and a range of ecological and environmental variables.
Results
Wing bones are longer in warmer climates. Our models, largely as a result of allometric effects, explain nearly all the variation in wing-bone length in our data, with a marginal R2 = 0.80 and a conditional R2 > 0.99.
Main Conclusions
Across 1520 species of birds, higher temperatures are associated with longer wing bones, as predicted by Allen's Rule. The vascularised musculature along these bones is maximally uncovered when birds actively hold their wings away from their bodies to aid in cooling or during flight. Conversely, the musculature along the wing bones is insulated by feathering when at rest, such that wings play a minor role in heat exchange when individuals are less active and may need to retain heat. While our analyses do not directly establish the mechanistic basis underlying the pattern we recover, given the asymmetry in the role of wings in thermoregulation, we interpret the positive relationship between temperature and wing-bone length to reflect increased demand for heat dissipation in warmer climates. Our findings highlight the role of thermoregulation in shaping even the most critical features of vertebrate anatomy.
The tendency for animals in warmer climates to be longer-limbed (Allen's Rule) is widely attributed to the demands of thermoregulation. The role of thermoregulation in structuring bird wings, however, has been overshadowed by the selective demands placed on wings by flight. We test whether occurrence in warmer climates is associated with longer wing bones.
Location
Global.
Time Period
Current.
Major Taxa Studied
Aves: Passeriformes.
Methods
Using computer vision, we measure wing-bone length from photographs of museum skeletal specimens for 1520 species of passerine birds. We then model the relationship between wing-bone length and temperature, accounting for allometry, the demands of flight efficiency and manoeuvrability, and a range of ecological and environmental variables.
Results
Wing bones are longer in warmer climates. Our models, largely as a result of allometric effects, explain nearly all the variation in wing-bone length in our data, with a marginal R2 = 0.80 and a conditional R2 > 0.99.
Main Conclusions
Across 1520 species of birds, higher temperatures are associated with longer wing bones, as predicted by Allen's Rule. The vascularised musculature along these bones is maximally uncovered when birds actively hold their wings away from their bodies to aid in cooling or during flight. Conversely, the musculature along the wing bones is insulated by feathering when at rest, such that wings play a minor role in heat exchange when individuals are less active and may need to retain heat. While our analyses do not directly establish the mechanistic basis underlying the pattern we recover, given the asymmetry in the role of wings in thermoregulation, we interpret the positive relationship between temperature and wing-bone length to reflect increased demand for heat dissipation in warmer climates. Our findings highlight the role of thermoregulation in shaping even the most critical features of vertebrate anatomy.
Date Issued
2025-04-01
Date Acceptance
2025-03-22
Citation
Global Ecology and Biogeography, 2025, 34 (4)
ISSN
1466-822X
Publisher
Wiley
Journal / Book Title
Global Ecology and Biogeography
Volume
34
Issue
4
Copyright Statement
© 2025 The Author(s). Global Ecology and Biogeography published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Identifier
10.1111/geb.70033
Subjects
Allen's rule
birds
flight
heat dissipation
macroecology
morphology
wing evolution
Publication Status
Published
Article Number
e70033
Date Publish Online
2025-04-04