Plumage pigmentation patterns of diurnal raptors in relation to colour ornamentation and ecology

While sexual signalling often compromises camouflage, some traits, including avian barred plumage, have been suggested to function simultaneously in camouflage and sexual signalling. Compared to coloration without pigmentation patterns, visual patterns are often beneficial for camouflage, and the precise arrangement of parallel bars in the pigmentation patterns of barred plumage may, at close range, provide cues on plumage quality useful for signalling. We used diurnal raptors, which benefit from camouflage for hunting in daylight, to test whether the evolution of some pigmentation patterns is associated with traits indicative of sexual selection. Phylogenetic regressions showed a negative association between the extent of barred and mottled plumage. There was also a negative association between the extent of ornamental colours and mottled plumage, thought to function mostly for camouflage, indicating a compromise between ornamentation and camouflage. The trade-off between ornamental colours and barred plumage was weaker than the one with mottled plumage, consistent with the hypothesis that barred plumage at times evolves for camouflage, similarly to mottled plumage, but at times can be co-opted for signalling together with ornamental colours. However, both barred plumage and ornamental coloration were only weakly related to socioecological traits suggestive of increased sexual selection. Therefore, despite differences in evolution between mottled and barred plumage in raptors, suggesting that the latter has more diverse functions than camouflage alone, behavioural research is needed to confirm the possible dual function of barred plumage as an ornamental trait.