Seasonal Changes in Colour: A Comparison of Structural, Melanin- and Carotenoid-Based Plumage Colours

Plumage coloration is important for bird communication, most notably in sexual signalling. Colour is often considered a good quality indicator, and the expression of exaggerated colours may depend on individual condition during moult. After moult, plumage coloration has been deemed fixed due to the fact that feathers are dead structures. Still, many plumage colours change after moult, although whether this affects signalling has not been sufficiently assessed.) displaying various coloration types (melanin-, carotenoid-based and structural). Birds were caught regularly during three years to measure plumage reflectance. We used models of avian colour vision to derive two variables, one describing chromatic and the other achromatic variation over the year that can be compared in magnitude among different colour types. All studied plumage patches but one (yellow breast of the blue tit) showed significant chromatic changes over the year, although these were smaller than for a typical dynamic trait (bill colour). Overall, structural colours showed a reduction in relative reflectance at shorter wavelengths, carotenoid-based colours the opposite pattern, while no general pattern was found for melanin-based colours. Achromatic changes were also common, but there were no consistent patterns of change for the different types of colours.Changes of plumage coloration independent of moult are probably widespread; they should be perceivable by birds and have the potential to affect colour signalling

Ultraviolet plumage ornamentation affects social mate choice and sperm competition in bluethroats (Aves: Luscinia s. svecica): a field experiment

The blue throat feathers of male bluethroats (Luscinia s. svecica) show a reflectance peak in the ultraviolet (UV) waveband (320 to 400 nm). The throat is actively displayed during courtship, suggesting a role for sexual selection on an ultraviolet signal. Indeed, a recent aviary experiment demonstrated that females discriminated against males with artificially reduced UV reflectance (Andersson and Amundsen 1997). Here, we report the results of a similar experimental manipulation applied on free-ranging males. UV-reduced (UVR) males had a lower success in attracting mates, as judged from a significantly later start of egg laying, compared with control (C) males. UVR males also spent significantly less time advertising for additional mates when their own mate was fertile, and they had a lower success in achieving extra-pair fertilizations. Furthermore, UVR males tended to guard their mates more closely and lose more paternity in their own brood than C males did. We conclude that the treatment affected both social and extra-pair mate choice. This is the first experimental evidence that UV signalling influences male mating success in free-ranging birds

Origin-related differences in plumage coloration within an island population of great tits (Parus major)

Several studies have described geographic variation in plumage coloration, providing important insights into the processes of local adaptation and speciation. Given that such variation appears to be common, individuals of different origin within a single population may vary accordingly. However, as yet no study has been able to test for such origin-related differences. The population of great tits (Parus major L., 1758) on the small Dutch island of Vlieland is especially suitable for such a study, as we know of every breeding adult whether it has been born on the island or not, and if it is, where on the island it was born. Furthermore, we have previously found large differences in clutch size and survival among birds of different origin in the same population. Here, we measured the spectral reflectance of the yellow breast feathers, and found that yearling, but not older, birds born in the eastern part of the island had feathers that were of a less bright yellow and UV than birds born elsewhere, irrespective of where they were breeding. Interestingly, this difference in coloration among yearlings of different origin shows a remarkable similarity with the genetic differences found earlier in this population with respect to clutch size and local survival. We thus show that systematic differences in color signals may exist within populations, among individuals of different origin, and we argue that it is crucial that such variation and its potential implications be accounted for irrespective of whether these differences have a genetic or an environmental basis. De nombreuses études ont décrit la variation géographique de la coloration du plumage et ainsi ouvert des perspectives importantes sur les processus d’adaptation locale et de spéciation. Comme ce type de variation semble être commun, les individus d’origine différente dans une même population peuvent varier en conséquence. Cependant, à ce jour, aucune étude n’a réussi à tester ces différences reliées à l’origine. La population de mésanges charbonnières (Parus major L., 1758), de la petite île hollandaise de Vlieland convient particulièrement à une telle étude, car on sait, au sujet de chaque adulte reproducteur, s’il est né ou non sur l’île et, si oui, on connaît l’endroit de sa naissance sur l’île. De plus, nous avons trouvé antérieurement de fortes différences dans les tailles des couvées et la survie parmi les oiseaux d’origines diverses dans cette même population. Nous mesurons ici la réflectance spectrale des plumes jaunes de la poitrine et observons que les oiseaux d’un an, mais non les plus âgés, nés dans la partie orientale de l’île ont des plumes de coloration jaune et UV moins vive que les oiseaux nés ailleurs, quel que soit l’endroit où ils se reproduisent. Ce qui est intéressant, c’est que les différences de coloration chez les jeunes d’un an d’origines différentes sont remarquablement similaires aux différences génétiques trouvées antérieurement dans cette population, en ce qui a trait à la taille des couvées et à la survie locale. Nous démontrons donc qu’il peut exister des différences systématiques dans les signaux de coloration dans les populations, parmi les individus d’origines différentes; nous croyons qu’il est essentiel de tenir compte de cette variation et de ses conséquences potentielles, que ces différences aient une base génétique ou environnementale