Uropygial gland volatiles facilitate species recognition between two sympatric sibling bird species

Visual and acoustic cues in birds have been well documented to play a role in species recognition between closely related bird species. Here, we aimed to test whether chemical cues also play a role in avian species recognition between 2 sympatric sibling species of waxwings, Bombycilla garrulus and Bombycilla japonica. Using gas chromatographymass spectrometry, we characterized from uropygial gland secretions 38 compounds that were quantitatively divergent between species and exhibited sex differences within species. Nine major compounds, including 6 linear alkanols and 3 carboxylic acids, which accounted for more than 85% of all compounds were used for simulation of the scents. Female B. garrulus exhibited a striking preference for their mirror images scented with either conspecific body odor or its synthetic analogs and avoided the scents of the sibling species B. japonica in a Y-maze olfactometer. Our results suggest that the volatile components of uropygial gland secretions have diverged in composition and these differences contribute to species recognition between sympatric sibling bird species and subsequently affect the likehood of speciation.