The Coloration of the Neck Feathers of Large-Billed Crows and Carrion Crows―the Color Variation Observed in Large-Billed Crows―

Although the neck plumage of crows appears mostly black, it can look green or blue when observed carefully. In this study, we examined the neck feather coloration of 55 Large-billed Crow Corvus macrorhynchos and 32 Carrion Crow Corvus corone captured in Tochigi and Kanagawa prefectures. Visual observation revealed that most Large-billed Crow had green, teal, or blue neck feathers, whereas most Carrion Crow had blue neck feathers. The reflectance spectra, brightness (L*), and chromaticity (a* and b*) were measured at three regions of the neck of each crow by spectroradiometer. Peak reflection occurred at 480.4 ± 32.5 nm for Large-billed Crow and 422.6 ± 15.3 nm for Carrion Crows, and the difference between species was significant. A scatter plot of chromaticity showed a strong correlation only in Carrion Crow. An analysis of covariance was performed to examine the difference in the correlation between a* and b*, and a significant species difference was found. The plots of Large-billed Crow distributed on the left side of the scatter plot comparing with the regression line of Carrion Crow. These results suggest that there is a species-specific difference between the neck feather coloration of these two species, with Large-billed Crow feathers varying from green to blue, whereas those of Carrion Crow were only blue. Further research is required to reveal the specific features of neck plumage color variation in crows, especially in order to understand the variation among individual Large-billed Crow.