Annual, sexual, size- and condition-related variation in the colour and fluorescent pigment content of yellow crest-feathers in Snares Penguins (Eudyptes robustus)

Abstract

Abstract. Colourful plumages observed in many birds provide ideal systems for investigating the control and function of animal signals, because we can identify the molecular currency (e.g. pigments, tissue structures) and thus the challenges associated with the production of the trait. To date, most attention has been paid to the signalling costs and benefits of the common pigmentary (e.g. carotenoid-and melanin-based) plumage colours. However, in penguins, the colour of feathers of crests or patches of head plumage is based on an unusual fluorescent pigment, presently thought to be in the class of pterin pigments, which are typically found as colourants in other animals like butterflies and amphibians. These yellow-orange colours may be used in sexual or social communication, but to date little is known about the signalling potential of such ornaments. We collected yellow crest-feathers from adult male and female Snares Penguins (Eudyptes robustus) in two years (2002 and 2003) and examined differences in colour and pigment content as a function of year, sex, body size and body condition. Unlike the typical pattern of birds, crests of female Snares Penguins contained higher concentrations of pigments than those of males. In both years, yellower feathers in females contained more yellow pigment. Birds of both sexes grew yellower and more pigment-rich feathers in 2002 -a year in which birds were in better condition -than in 2003. Males with yellower crests also tended to be larger, heavier and in better condition, regardless of year. These results highlight the potential for yellow crests in Snares Penguins to serve as a condition-dependent indicator to conspecifics. Further work is needed to determine whether or not this plumage trait is a signal of social status or attractiveness, as colourful plumage patches appear to be in other penguin species.

Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

“…For example, the yellow feathers in great (Aptenodytes), crested (Eudyptes) and yellow-eyed (Megadyptes) penguins are important to both sexes for mate selection and can reveal individual quality [17,29,30,84]. The colour-based sexual selection strategy probably evolved once in a stem-penguin lineage and was retained by members of the penguin crown group, including extinct Madrynornis mirandus.…”

“…Furthermore, yellow plumage pigmentation is a condition-dependent trait [28][29][30] and is important to the sexual selection criteria of half the living penguin genera [31][32][33][34]. Thus, further characterization of the chemical identity of this pigment could provide clues into the costs, benefits and evolution of these display traits.…”

Beak color dynamically signals changes in fasting status and parasite loads in king penguins

“…; unpublished data). YO colors are often produced by exogenous carotenoid pigments, which are acquired from the diet and may reflect yearly environmental forage conditions (Linville and Breitwisch 1997;McGraw et al 2009;Slagsvold and Lifjeld 2009). In king penguins, similar mechanisms might explain variation in YO color production between years (i.e., higher YO color in years of high resource availability; Keddar, Couchoux, et al 2015).…”

Variation of mutual colour ornaments of king penguins in response to winter resource availability

“…Colours of ornamental feathers appear to be pterin-based and the orange colour of the beak spot carotenoid-based (McGraw et al, 2004(McGraw et al, , 2007Thomas et al, 2013). Moreover, saturation has been related to the concentration of pterins in Snares penguin coloured feathers (McGraw et al, 2009), and to the concentration of carotenoids in mallard beaks (Butler et al, 2011). Thus from a mechanistic point of view, our results may suggest a lower allocation of pterins to feather ornaments during the unfavourable year, while maintaining the carotenoids allocation to the beak spot nearly constant.…”

“…Saturation is a measure of spectral purity, and indicates the degree to which a colour appears as composed of single wavelength. This measure has been related to the pigment content of ornaments in a few species (e.g., yellow feathers of Snares penguins, Eudyptes robustus, McGraw et al, 2009; beaks of mallards Anas platyrhynchos, Butler et al, 2011). Brightness is a measure of spectral intensity that indicates the total amount of light coming from an ornament.…”