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Migratory birds hit a wall of light

October 1, 2022 Don Knowler

Gazing up at the twinkling stars on Sunday night it was hard to imagine that light pollution was emerging as a major menace to birds across the world.
The Milky Way meandered across the sky and I was confident that bright and piercing light would not disrupt the journeys of birds travelling to southern Tasmania.
It’s not the same in most other cities which are blighted by artificial light.
Birds navigate by a combination of the stars, the position of the sun and the earth’s magnetic field and landmarks like rivers, hills and mountains. But night pollution has been found to be disrupting these nocturnal journeys, principally by causing disorientation as birds cross the skies. A major threat are high-rise buildings throwing out bright light in our cities, although lighthouses and illuminated oil rigs can cause a hazard at sea.
Migrating birds are attracted to artificial light, particularly when there are low cloud conditions, fog, rain, or when flying at lower altitudes. This lures them to hidden dangers in our cities.
Because birds become disorientated, they often end up circling in illuminated areas. With their energy reserves depleted, they risk exhaustion, or worse. And birds are also prone to collision with the buildings themselves.
Light pollution is estimated to cause the death of millions of birds annually and this year an annual celebration of the wonders of birds migration, World Migratory Bird Day, is setting out to draw attention to this avian toll. The event, taking place on Saturday, is promoting “natural darkness” as a conservation issue as vital as clean water, air and soil.
Currently, more than 80 per cent of the world’s population is estimated to live under a “lit sky”, and the figure is closer to 99 per cent in western developed countries.
The migratory bird celebration is organised by a range of conservation organisations across the globe, under the umbrella of the United Nations Environmental Program. The UN’s involvement makes the point that migratory birds travel across borders, inspiring and connecting people along the way.
And people are listening, especially those who run our cities and the owners of the high-rise buildings. More and more cities worldwide are taking measures to dim building lights during migration phases in spring and autumn.
Most songbirds migrate at night when there are fewer predators about, although many scientists believe the main reason is that the stars help orient them on their journeys.
Among migrants are the tiny silvereyes which build in number in Tasmania at this time of year, boosting others which have overwintered.
Because of a distinctive feature enhancing their moss-green and silver plumage – russet feathers on their flanks – it is known that the Tasmanian silvereye sub-species spends its winter in southern Queensland.
On starlit nights in September I look to the skies and know the silvereyes and the other migrants are on their way.

On The Wing

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