Another Life: What does whiteness tell us about wildlife?
Natural selection should keep only changes that improve survival. But how, in the evolution of swans from small dinosaurs, did the four northern swan species go white while those in the southern hemisphere sprout some dark feathers and the native swan in Australia is mostly black?
Chilled: snowy owl carries the spirit of cooler climates. Illustration: Michael Viney
Flying low into the wind along the shore, to change one salty lake for another, a line of whooper swans make a ripple of whiteness even brighter than the crests of surf piled up behind them. The wildness of the shore at this time, with flashes of water in every fold of land, send my thoughts up the coast to the tip of Mayo’s Mullet peninsula, where another big white bird often visits in winter.
The snowy owl can seem, perhaps, the whitest bird of all, whether perched on a High Arctic boulder or a rock beside the henge on the brow of Falmore Hill. Like the barnacle geese on the neighbouring Inishkea islands, and the Arctic gyrfalcon, another snowy hunter that follows them there, the owl seems to carry the spirit of chillier latitudes.
The whiteness of so much wildlife is full of paradox and mystery. One seeks to know what the whiteness is “for”, as natural selection should keep only changes that improve survival. But how, in the evolution of swans from small dinosaurs, did the four northern swan species go white while those in the southern hemisphere sprout some dark feathers and the native swan in Australia is mostly black?
In the High Arctic, white animals and birds seem to make more obvious sense: whiteness is for camouflage in all that snow and ice, right? But big groups of perennially white hares nibbling poppies on the bog-brown summer tundra could not be more conspicuous. Then, it is the sheer speed of the adults (up to 64km/h) that can save them from foxes and wolves. And it was not camouflage but bitter cold that turned parts of many Irish hares white in the exceptionally hard winter a couple of years ago.
The polar bear, clearly, is not worried about predators; nor does it always look white, depending on the slant of the sun. A mother and daughter I watched from a cliff in northeast Greenland seemed beautifully tinged with gold. The outer hairs of the polar bear’s fur are shiny and stiff, quick to shed water at a shake. They are also hollow, like fine light tubes, and carry short-wavelength energy from the sun to the bear’s black skin. The animal mainly has blubber to keep it warm, but the hollow hairs may also play a part in thermoregulation.
Wolves, foxes and the stoat family all tend to get paler, or even white, the farther north they range, but whiteness in birds, whether whole or in patches, can serve many purposes, from the Arctic to the tropics. Whiteness itself is an absence of colour – keratin, the substance of feathers, is naturally transparent and scatters all frequencies of the spectrum visible to the human eye. Coloured feathers have structures that reflect light selectively or are filled with granules of melanin pigment.