Data and code for: Plumage balances camouflage and thermoregulation in Horned Larks (Eremophila alpestris)

Animal coloration serves many biological functions and must therefore
balance potentially competing selective pressures. For example, many
animals have camouflage in which coloration matches the visual background
that predators scan for prey. However, different colors reflect different
amounts of solar radiation and may therefore have thermoregulatory
implications as well. In this study, we examined geographic variation in
dorsal patterning, coloration, and solar reflectance among Horned Larks
(Eremophila alpestris) of the western United States. We found that plumage
brightness was positively associated with soil granularity, aridity, and
temperature. Plumage redness—both in terms of saturation (i.e., chroma)
and hue—was positively associated with soil redness and temperature, while
plumage patterning was positively associated with soil granularity.
Together, these plumage-environment associations support both background
matching and Gloger’s Rule, a widespread ecogeographic pattern in animal
coloration. We also constructed thermoregulatory models that estimated
cooling benefits provided by solar reflectance profiles of the dorsal
plumage of each specimen based on the collection site. We found increased
cooling benefits in hotter, more arid environments. Finally, cooling
benefits were positively associated with residual brightness, such that
individuals that were brighter than expected based on environmental
conditions also had higher cooling benefits, suggesting a tradeoff between
camouflage and thermoregulation. Together, these data suggest that natural
selection has balanced camouflage and thermoregulation in Horned Larks and
illustrate how multiple competing evolutionary pressures may interact to
shape geographic variation in adaptive phenotypes.