Data for: Allometry reveals trade-offs between Bergmann’s and Allen’s rules, and different avian adaptive strategies for thermoregulation

Animals tend to decrease in body size (Bergmann’s rule) and elongate
appendages (Allen’s rule) in warm climates. However, it is unknown whether
these patterns depend on each other or constitute independent responses to
thermal environment. Here, based on a global phylogenetic comparative
analysis across 99.7% of the world’s bird species, we show that the way in
which the relative length of unfeathered appendages co-varies with
temperature depends on body size and vice versa. First, the larger the
body, the greater the increase in beak length with temperature. Second,
the temperature-based increase in tarsus length is apparent only in larger
birds, whereas in smaller birds, tarsus length decreases with temperature.
Third, body size and the length of beak and tarsus interact each other to
predict the species’ temperature preferences. These findings suggest that
the animals’ body size and shape are products of an evolutionary
compromise that reflects distinct alternative thermoregulatory
adaptations.