The uguisu is a small passerine bird that is native to East Asia. It is known for its distinctive call that sounds like the Japanese words “ho-ho-ke-kyo”, which has led to it being given names such as the Japanese bush warbler or Japanese nightingale. But beyond its beautiful song, the uguisu is also recognizable for its unique plumage. So what colour is a uguisu? Let’s take a closer look at this fascinating bird.
The Male Uguisu’s Vibrant Colour
The most striking feature of the male uguisu is its bright colouration. While the females and juveniles have more subdued, olive-brown plumage, the adult males are a vivid shade of greenish-yellow on their wings, back, rump, and tail. Their underparts are a lighter whitish-yellow. On their heads they have a distinctive black mask-like facial pattern with white patches above and below the eye.
So in summary, the predominant colour of the male uguisu’s plumage is a bright, lemon-lime yellow. When they flit through the forest canopy, it’s hard to miss that burst of vibrant chartreuse among the greens. The male’s flashy feathers likely serve to attract mates and proclaim territory.
Seasonal Colour Changes
While the male uguisu’s yellow breeding plumage is their most well-known trait, their colour is not static throughout the year. During the non-breeding season, the males moult into a more subdued grey-green and white plumage. This helps them blend in and be less conspicuous outside of mating season. Then in spring, they moult back into their bright breeding colours to attract females.
So the answer to “what colour is a uguisu?” depends on the season! In breeding season, males are typically a vibrant yellow-green. In non-breeding months, both males and females take on more neutral soft greys and olive hues better suited for camouflage.
Geographic Variation in Colour
Adding another layer of complexity, uguisu colour can also vary across their geographic range. For example, the nominate subspecies in Japan has very yellow males in spring. But some subspecies found in more northern areas, like P. u. taczanowskius on Sakhalin Island, have darker olive-green males. Meanwhile, southern subspecies like P. u. omeiensis from China are generally paler yellow above with whiter underparts.
So while the bright springtime breeding plumage of Japanese uguisu remains the most iconic, ornithologists recognize up to 30 subspecies across the bird’s distribution, each with its own subtle variations in colour and patterning. Geography and genetics influence their diverse palette.
Diet Influences Colour
In addition to seasonal and regional diversity, another factor that can affect uguisu colouration is diet. Carotenoid pigments obtained from their food are what produce the yellows and oranges in their feathers. Uguisus feed on insects and fruit, both of which provide carotenoids.
So the richness of yellow in a male’s plumage may correlate with the availability of carotenoid-rich prey in his territory. Males who can secure more vibrantly pigmented foods may accordingly develop more colourful feathers, which could signal their health and fitness when trying to attract a mate. A male with duller coloration may be lacking key carotenoids in his local habitat.
UV and Near-UV Elements
Our human eyes only see a portion of the avian visual spectrum. Researchers using UV cameras and spectrometry have revealed that many bird feathers have “hidden” UV reflective elements we cannot perceive. This is true of the uguisu’s plumage as well.
While they appear yellow-green to us, their feathers have additional UV reflections. The UV sheen may enhance signalling between birds in mate selection and territorial interactions. So the uguisu’s colour palette incorporates both human-visible elements and UV channels only other birds can fully appreciate.
Shiny Structural Colours
In addition to pigmentary colours from carotenoids, uguisu plumage incorporates structural colours. Their feathers contain nanoscale tissue structures that refract and reflect select wavelengths of light. This produces a shimmering, iridescent sheen.
Dramatic examples include the glossy blue-green patches on their secondaries and tail feathers. These structurally-produced hues augment and interact with the yellow pigments to create their overall colourful appearance. The mix of structural “metallic” colours and pigmentary colours allows uguisus to achieve their aesthetic brilliance.
A Disguise Against Predators
So in summary, the breeding male Japanese uguisu is most readily distinguished by its bright yellow-green plumage accented with a dark facial mask. But this conspicuous colour is only worn temporarily each spring.
Outside breeding season and in other parts of their range, uguisus take on less flashy plumage. Duller female-like colours likely help male uguisus survive unnoticed against predators when they are not trying to attract a mate.
Their distinctive melodious call remains constant, but uguisu colour changes strategically with the seasons to balance sexual display with camouflage. Their colour variability highlights the adaptable selective pressures shaping their appearance.
Conclusion
Through intricate seasonal moults, carotenoid diet, and structural feather attributes, the uguisu produces a complex and dynamic range of colours. Subtle variations distinguish subspecies across eastern Asia. But the quintessential image remains the Japanese breeding male, with its brilliant fluorescent yellow and black mask – a living ornament emblematic of spring. The uguisu’s colour is not singular, but reveals an intricate interplay of genetic adaptation, seasonal imperatives, visual communication, feeding ecology, and predators. Its colour spans the avian visual world, incorporating human-visible hues modified with ultraviolet and structural effects. In the end, the multifaceted colour of the uguisu reflects the bird’s own diverse biology and natural history.