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

Abstract

BackgroundPlumage 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.Methodology/Principal FindingsWe studied changes in coloration after moult in four passerine birds (robin, Erithacus rubecula; blackbird, Turdus merula; blue tit, Cyanistes caeruleus; and great tit, Parus major) 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.Conclusions/SignificanceChanges of plumage coloration independent of moult are probably widespread; they should be perceivable by birds and have the potential to affect colour signalling.

Is oxidative status influenced by dietary carotenoid and physical activity after moult in the great tit (Parus major)?

“…Feathers are passive structures and variation in their coloration is due to pigment composition and concentration, which reflects the type and quantity of carotenoids ingested during moult (Hill and McGraw, 2006;Peters et al, 2007). Feather coloration may also change after moult (Galván and Sanz, 2006;Delhey et al, 2010). Few studies have explored variation in carotenoid-based colour after moult (Hill and McGraw, 2006;Peters et al, 2008;Delhey et al, 2010).…”

“…Feather coloration may also change after moult (Galván and Sanz, 2006;Delhey et al, 2010). Few studies have explored variation in carotenoid-based colour after moult (Hill and McGraw, 2006;Peters et al, 2008;Delhey et al, 2010). Previous studies have experimentally shown that feathers exposed to sunlight become less yellow (Surmacki, 2008;Surmacki et al, 2011) probably due to an effect of pigment oxidation caused by photon absorption.…”

“…However, although many studies document the positive relationship between coloration and body condition or immune system, not all confirm these findings (Hõrak et al, 2004;Isaksson et al, 2005;Geens et al, 2009). Mechanisms underlying seasonal variation in coloration are not yet well understood, but some hypotheses have been advanced, such as UV bleaching, and bacterial or mechanical degradation (Delhey et al, 2010). In great tits, the brightness of the yellow coloration has been shown to increase with the size of the uropygial gland (Galván and Sanz, 2006), which produces an oil that birds deposit on their feathers, its size and oil composition varying with microbiome composition (Jacob et al, 2014).…”

“…Here, the ratio of heterophils to lymphocytes (hereafter H/Ly) was used as an index of physiological stress Davis et al, 2008), and blood sedimentation rate was used as an index of immune system activation (Glick, 2000). Finally, because plumage colour has recently been shown to be a dynamic trait (Galván and Sanz, 2006;Delhey et al, 2010), in order to test for any potential effect of our treatment, we decided to measure feather colour at the beginning and at the end of the experiment. As metabolism is linked with body size (Peters, 1986) and physical activity modifies body condition (Verspoor et al, 2007), body mass and tarsus length were used as covariates.…”

Evolution of long-term coloration trends with biochemically unstable ingredients

“…by microbial activity, physical damage, UV exposure) progressively exposes embedded carotenoids to additional oxidization, and thus produces colour change despite the lack of additional pigment input [17][18][19][20][21]. An important discovery is that different carotenoid types within a feather have different potential for UV and oxygen modification, with some carotenoids remaining remarkably stable once deposited in feathers whereas others change readily, considerably modifying the appearance of the plumage [20][21][22]. The biochemical stability of carotenoids typically increases with metabolic modification [23,24], including those commonly accomplished by birds [25].…”