Ultraviolet-blue plumage colouration can be perceived as an indicator of fluctuating asymmetry by Blue Tits ( Cyanistes caeruleus).

The expression of structural plumage colours (i.e. those generated by feather microstructures) often acts as a signal of quality, but the signal content of these traits remains relatively unknown. However, a hypothesis posits that the production of structural colouration depends on developmental stability because variation in developmental programs can affect the precise feather structures that generate structural colour. Here, I test this hypothesis by exploring the relationship between crown colouration, calculated by using a model of avian visual perception, and fluctuating asymmetry (FA) of tail feathers in Blue Tits ( Cyanistes caeruleus). As predicted, there was a negative correlation between the ultraviolet (UV)-blue reflectance of the crown patch and FA of feathers. There was indirect evidence for a relationship between fledging success and UV-blue colour, but not for a condition dependence of this trait. These results suggest that the signal content of the structural colouration of Blue Tits may be information regarding individuals' developmental stability. As the colour components of the crown colouration were calculated with an avian visual perception model, this indicates that Blue Tits can perceive differences in FA through variation in the expression of structural colour. [ABSTRACT FROM AUTHOR]