Phylogenetic signature of uropygial gland size in a North American bird community

The uropygial gland and the oils secreted from it have been shown to serve important functions in many bird species including plumage maintenance and chemical communication. Previous species comparisons of uropygial gland size have only been conducted in South American and European communities and have found little to no phylogenetic signature. Here, we document uropygial gland measurements of 35 different species and 1 hybrid chickadee population in eastern Pennsylvania, most of which are reported for the first time. Uropygial gland size is related to overall body size, controlling for phylogenetic relatedness, but not to sex or season. We demonstrate a significant phylogenetic signature of relative uropygial gland size. Clades with larger than expected gland size for their body mass included the Paridae and select species in the Passerellidae and Parulidae, which have been shown to particularly rely on olfactory cues in a variety of ecological contexts. In contrast, we found that the Turdidae have smaller than expected gland sizes, possibly reflective of other life history traits such as ground foraging and nesting. Our results are consistent with previous species-specific studies of olfactory-based behaviors and additional life history traits and we believe that the size of the uropygial gland could be a good indicator of the differential importance and use of the uropygial gland in bird species.