Melanin-Based Iridescent Feather Color in the Jungle Crow

Abstract

ABSTRACT. Sexual differences in Japanese Jungle Crows (Corvus macrorhynchos) are not obvious because both sexes have black plumage. However, closer examination reveals that their plumage color is not only black; it is also iridescent color. Furthermore, the iridescence is more pronounced in adult males than that in females. The iridescence seems to be related to the density and concentration of melanin granules. The density of melanin granule and the concentration of eumelanin in feathers were significantly higher in males than that in females (P<0.01). However, the amount of pheomelanin was below the detection limits in this study.KEY WORDS: crow, feather color, HPLC, melanin.J. Vet. Med. Sci. 71(9): 1261-1263, 2009 Melanin is the most abundant and widespread pigment in birds. The 2 basic types of melanin pigments are eumelanin and pheomelanin [8]. Black and gray feathers are typically thought to contain mostly eumelanins, whereas earth-toned feathers are dominated by pheomelanins, much like red human hair [1]. The relationship between feather color and melanin pigments has been studied by various researchers. Hasse reported [2] melanin concentrations in wild rock pigeons (Columba livia) and domestic pigeons. McGraw and Wakamatsu measured melanin concentrations of zebra finches (Taeniopygia guttata) feathers color [6], and also reported melanin concentrations in the feathers both sexes of European barn swallows (Hirundo rustica rustica) [7].Although, jungle crows (Corvus macrorhyncho) have melanin-based iridescent black feathers coloration, it's not known as to how much they have the melanin concentration and whether they have sexual differences in the amount of melanin concentration and density. The present study examined whether any sexual differences exist in the feathers of jungle crows, using electron microscopy and high performance liquid chromatography (HPLC).Adult jungle crows of both sexes were captured from January 2005 to November 2006 at Niiza city, with permission of the Saitama prefecture (Permit to capture of wild animals No. 01-02), and kept in a laboratory animal facility. The sex of each bird was confirmed by gonad examination after dissecting. The secondary feathers (the feathers that adhere to the ulna) were removed from each individual under anesthesia with pentobarbital (35mg/kg) and the feathers were washed under running water and stored under dry cool conditions until analysis.First, we used electron microscopy to determine the microstructure of the feather barbules. For this study, five adult males and four adult females were used. We cut the upper 0.5 cm of the barb of 5 barbs from the secondary feathers of each bird. The feather barbs were immersed in 0.1% Tween-20 for 1 hr followed by 0.25 M sodium hydroxide. These barbs were fixed with 1% osmic acid solution for 24 hr after immersion in 2.5% glutaraldehyde for 48 hr. They were dehydrated in ethanol (70%, 80% and 90%) and then rinsed in 90% ethanol: 90% acetone (1:1 v/ v), followed by 90, 95 and 100% acetone. They were then immersed ...

Nanostructural self-assembly of iridescent feather barbules through depletion attraction of melanosomes during keratinization

“…In addition, because keratin is the main cytoskeleton protein in keratinocytes [53,54], its concentration may also affect their elliptical cross-sectional shape. We further predict that barbules with thin-film iridescence should have a greater volume fraction of melanosomes than noniridescent barbules, and this is supported by evidence from a comparison of iridescent and non-iridescent barbules from jungle crows (Corvus machrorhynchos; [55]) and population-level variation in the chestnut-bellied monarch (Monarcha castaneiventris; [56]). Finally, the interactions between depletion attraction and other short-range forces (such as Coulombic forces) may contribute to the diversity of iridescent structures.…”

Enhanced photothermal absorption in iridescent feathers

“…However, temperature increased considerably less with shape than with melanin content. Therefore, the large number of melanosomes in iridescent feathers [32,33] likely explains their higher surface temperatures after radiative heating, with shape and structural effects playing only a minor role.…”

“…Due to the highly absorptive properties of melanin [31], we hypothesized that melanin-based feathers would absorb more light, and heat more, than feathers with other pigments (carotenoids) or without any pigment (whites) (figure 1). Within melanin-based feathers, we hypothesized that nanostructured iridescent feathers would heat more due to greater amounts of melanin within the feather barbules [32,33], their lower reflectance in the near-infrared [24] and plasmonic photothermal effects (i.e. highly localized conversion of light to thermal energy) [22].…”