# Dressed for the Weather: Tawny Owl Feather Adaptations Across a Climatic Gradient

## TL;DR

Tawny owls in colder regions have feathers that may help them stay warm, suggesting local adaptation to climate.

## Contribution

The study shows that feather properties, not coloration, may reflect local adaptation in tawny owls across Europe.

## Key findings

- Feather structures showed more phenotypic divergence than expected from genetic drift.
- Colder populations had larger plumulaceous parts in dorsal feathers, suggesting better insulation.
- Plumage color variation showed little divergence, indicating limited role of natural selection in coloration.

## Abstract

Populations are presumed to be adapted to local environmental conditions via natural selection, with gene flow breaking up local adaptations. In birds, various aspects of feathers may reflect local adaptation. For example, the insulation capacity of feathers could be greater in colder regions, while colour variation may also play a role in adapting to local environmental conditions since darker feathers are known to absorb more heat than lighter ones. We studied feather properties (plumulaceous part of the feather, density of barbs and barbules) of tawny owl,
Strix aluco
, across nine populations covering a large part of the species' European range (9–52 individuals per population) as well as their plumage colour, scored as dark (brown) versus light (grey) morphs. We compared these traits' phenotypic divergence (PST) with the divergence expected based on genetic drift (FST) inferred using eight microsatellites. The FST was low (0.022; 95% CI 0.005–0.039), and most feather structures' phenotypic divergence (PST) exceeded the FST. However, phenotypic divergence in plumage colour was low and not significant, implying a limited role of natural selection in shaping variation in plumage colouration at large spatial scales. Between‐population differentiation in feather properties was more pronounced in ventral feathers than dorsal feathers. In colder populations, the plumulaceous part of the dorsal feathers, but not the ventral feathers, was larger (implying greater insulation). Although proper evaluation hinges on understanding how insulative properties confer a fitness advantage in a given environment, our findings imply that properties of avian feathers may reflect local adaptation, possibly related to climate.

Populations of tawny owls may exhibit local adaptations in feather properties, with variations in insulation and colouration linked to environmental factors like temperature. Our study across nine European populations showed significant phenotypic divergence in feather structures, but minimal divergence in plumage colour, suggesting limited natural selection's role in shaping colouration at larger spatial scales. The findings indicate that feather properties, particularly in colder regions, may reflect local adaptation, possibly related to climate, though further research is needed to assess their functional role in fitness.