To be on this side of the winter solstice, however imperceptible the lengthening of the daylight hours, fills me with relief. The sun’s slow return has begun, and I’m looking forward to the light lingering longer in the day. Then again, there are the next few months to get through, which can feel static, sullen and still. So I take to the mountains, hoping a bit of altitude will compensate for winter’s fleeting light.
Passing through a small broadleaved woodland, a flash of azure draws my attention to the midsection of an oak tree. Perched on a branch, leaning forward as if in a mad dash to its next destination, is a jay, otherwise known in Irish as scréachóg choille, the woodland screecher. Jackdaw-sized (it belongs to the same family), this exotic-looking species appears a rather unlikely bird to be found in Ireland. On the occasions I’ve spotted one, it reminded me of a budgerigar that has escaped captivity only to find itself in a damp, mossy Irish wood.
Jays give off the sense of being perpetually preoccupied, always on their way to something more urgent and important than resting on an oak branch, singing a tune. Argumentative and noisy, they’re the lovable gangsters of the forest and give off a general sense of being up to no good. This one allows me the briefest of glances before it nimbly shoots out of view, but not before I spot its blinged-out band of electric-blue wing feathers: a raucous bird of paradise in a Wicklow woodland.
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Thankfully, they’re doing all right in Ireland; having expanded their range over the past few decades, they’re found in woodlands across the country. They’ll eat insects, fruits, reptiles and eggs of other birds, but they always favour the nut of the oak tree, acorns packed with healthy fats (like those in olive oil and fish) and essential proteins.
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When acorns fall from the oak tree in autumn, a jay will hide up to 5,000 of them around the wood, using the arboreal space as a kind of secret larder for winter’s colder months, when high-quality food is hard to come by. The acorns they don’t eat will grow upwards, and jays are like guerilla tree planters, disseminating oak genetics far and wide.
The markings and colours of jay feathers are dashes, dots and streaks of black and rufous-brown. But it’s the unmistakable dazzling blue wing feathers, gleaming like a sapphire bracelet, that instantly gives them away. What’s fascinating about this blue is that it exists, in many ways, as a kind of play of light, nature’s optical illusion.
Two pigments create various colours in birds and other species such as butterflies. Melanin produces dark, earthy tones of browns, blacks and greys; another pigment, carotenoid, produces bright oranges, reds and yellows. But the greens and blues seen in many species, including the jay and the vivid iridescent feathers of the peacock, aren’t from pigments at all; they appear because of the feather’s shape and the way it interacts with the light.
The first person to notice this was English scientist Robert Hooke, who wondered why the colour of a peacock’s feather changed and shimmered depending on the angle of the light (similar to how a soap bubble changes colour in a bath or an oil slick appears at sea). And so, one afternoon in 1665, Hooke put the feather on the stage of the recently invented microscope and peered down.
What he saw wasn’t a smooth surface but a multitude of layered, minuscule filament-like barbs arranged in a way that reflects and refracts light as it travels through. It’s like holding a shiny DVD in one hand and tilting it towards the light. It will wink back at you in iridescent splendour with a rainbow of colours. There’s no pigment or paint on its surface; instead, the tiny grooves on the surface cause light to scatter and spread into its spectrum of colour.
This “structural colour” phenomenon explains why the jay in the wood has blue in its wing feathers. In many birds, just as in butterflies, the colour depends on the thickness of the tiny layers. In butterflies, thicker scales amplify blues and greens; the same goes for feathers. The microscopic structures in the jay’s wing feathers, made of keratin, are just the right size to reflect blue, and it does so in a vibrant and exotic way that doesn’t fade over time. Textile researchers are exploring whether structural colour could be used in the fashion industry as an alternative to harmful and polluting chemical dyes.
The oak wood where the jay lives is behind me, and I trek up the mountain’s steep slope. Below, a thick covering of fog spreads out across the lowlands like a layer of newly sheared white wool. The late morning winter sun pushes out through the grey clouds and offers a weak pulse of warmth. Spring will be with us soon.