Some migrating bird species are becoming increasingly attracted to city life, yet these unnatural habitats can be lethal. Every autumn, Swainson’s thrushes migrate from the north to central and northern South America. Some, though, make “pit stops” in and around towns like Montreal.

Morales, a doctoral student at McGill University, and her colleagues investigated how Swainson’s thrushes combine the need to migrate quickly – in order to maximize their benefits – with the need to recharge, such as by stopping in areas like Montreal, for a paper published last month. Thousands of migrating birds stop in cities all over the world as part of their incredible trips that can traverse thousands of kilometers. It’s not always clear why they choose to live in cities. Some appear to be drawn to light. Others, like the Swainson’s thrush in its berry-filled bush, appear to enjoy the food available. However, cities are not always welcoming to visitors.

Unfortunately, the death toll is alarming. Domestic cats, for example, kill some migrating birds, while others collide with structures. So, how can we make cities more like travel lodges for these animals, rather than death traps? Morales and her colleagues discovered that Swainson’s thrushes stop in Montreal for remarkably extended periods of time, where many of the birds molt — a process in which the birds shed and regenerate some of their feathers. This helps them prepare for the long journey ahead. It’s the equivalent of getting a new set of tires for your car.