Paper on functional morphology of body feathers accepted in Functional Ecology

Authors marked in boldface are EvolEcol members, authors with asterisk are undergrad students.

Pap PL, Vincze O, Wekerle B*, Daubner T*, Vágási CI, Nudds RL, Dyke GJ and Osváth G 2017. A phylogenetic comparative analysis reveals correlations between body feather structure and habitat. Functional Ecology (in press).

Summary
1. Body feathers ensure both waterproofing and insulation in waterbirds, but how natural variation in the morphological properties of these appendages relates to environmental constraints remains largely unexplored. Here, we test how habitat and thermal condition affect the morphology of body feathers using a phylogenetic comparative analysis of five structural traits [i.e., total feather length, the lengths of the pennaceous (distal) and plumulaceous (proximal) sections, barb density, and pennaceous barbule density] from a sample of 194 European bird species.
2. Body feather total length is shorter in aquatic than in terrestrial birds, and this difference between groups is due to the shorter plumulaceous feather section in aquatic birds. Indeed, a reduced plumulaceous section in feather length probably reflects the need to limit air trapped in the plumage to adjust the buoyancy of aquatic birds. In contrast, the high pennaceous barbule density of aquatic birds compared to their terrestrial counterparts reflects water resistance of the plumage in contact with water.
3. Our results show that birds living in environments with low ambient temperature have long plumulaceous feather lengths, low barb density, and low pennaceous barbule density. Data also suggest that plumage probably has limited function in reducing the heat absorption of species living in hot environments.
4. Our results have broad implications for understanding the suite of selection pressures driving the evolution of body feather functional morphology. It remains to be tested, however, how other feather traits, such as the density of plumage (feathers per unit area) and the relative number of different feather types, for example downy feathers, are distributed amongst birds with different water resistance and thermoinsulative needs.

Key-words: body feathers, feather lengths, functional morphology, thermal insulation, vane density, water repellence

Figure 1. Different parts of a body feather with distal pennaceous and proximal plumulaceous sections delimited by a white stripe across the rachis at the base of the barb in which the length was at least 33% plumulaceus. The black lines define the boundary of the pennaceous and plumulaceous sections of the vane (a,b). Upper figures show two typical species with the ratio of the pennaceous feather section to plumulaceous part. In the Common Raven (Corvus corax), a terrestrial species, the plumulaceous part is longer (a), while in the Common Moorhen (Gallinula chloropus), an aquatic bird, this feather part is reduced in length (b). Lower figures illustrate a section of pennaceous vane with the rachis and barb to which the barbules attach. The density of pennaceous barbules are lower in terrestrial species, such as the Common Buzzard (Buteo buteo) (c) than in aquatic birds, represented here by the Northern Pintail (Anas acuta) (d). Scale bars for figures (a) and (b) are 1 cm, and for (c) and (d) are 0.5 mm.