The strange reason migrating birds are flocking to cities
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Ana Morales stepped through the shrubbery, scanning the airwaves with a radio receiver. The device had picked up a signal from a transmitter that she and colleagues had previously attached to a Swainson's thrush, a small brown and white speckled bird native to the Americas. The same signal had popped up on Morales' handheld receiver a few days earlier, emanating from exactly the same bush in a park on the edge of Montreal in Canada.
This was a worry. It seemed so unlikely that the transmitter remained attached to a live bird – more likely, it had fallen off and was hanging on a branch. Just to make sure, Morales, a graduate student at McGill University, gave the berry-laden shrub a gentle shake – and then a flutter of feathers among the branches and shadows caught her eye. To her surprise, the thrush, very much alive and healthy, was hopping about the bush in protest at having been disturbed. This little bird had hung around for longer than she expected.
Swainson's thrushes migrate from northern areas to Central and northern South America every autumn. But some make a "pit stop" in and around cities such as Montreal. For a study published last month, Morales and her colleagues had been researching how Swainson's thrushes balance the need to migrate quickly – so as to maximise its benefits – with the need to refuel, such as by stopping over in places like Montreal. They caught and radio tagged a total of nearly 80 of the birds.
Huge numbers of migrating birds visit cities all around the world on their extraordinary journeys, which often cover thousands of kilometres. It is not always obvious why they come to urban locations. Some appear to be attracted by light. Others, such as the Swainson's thrush in its bush full of berries, seem to enjoy the food on offer. But cities are not always friendly to outsiders.
https://www.bbc.com/future/article/20220217-the-strange-reason-migrating-birds-are-flocking-to-cities
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And why you might find unexpected species right in your own backyard!
