Study reveals how Canadian songbirds change their bodies during migration

Researchers at Western University’s Advanced Facility for Avian Research explore how much songbirds’ bodies can change to fly higher when migrating

A yellow-rumped warbler perches on a branch near Kamloops, B.C. (Photo: Amanda Nelson/Can Geo Photo Club)
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Migratory birds are extraordinary endurance athletes. Not only is their migration one of the riskiest and most energetically demanding feats in all the wildlife kingdom, but in making this journey they outpace any mammal’s aerobic performance by far. The blackpoll warbler is one of the champions of North American migratory songbirds, managing average southbound flights of 2,540 kilometres over 62 non-stop hours, all while weighing just 12 to 14 grams — about the same as a triple-A battery. While the journey has always been perilous, today’s climate conditions — including scorching heat, smoke from wildfires, more violent storms and more intense droughts — make it even more challenging.

How birds respond to their changing environment is the subject of groundbreaking research at Western University’s Advanced Facility for Avian Research in London, Ont. Postdoctoral researcher Catherine Ivy is investigating seasonal changes in bird physiology that allows them to overcome some of these dangers by flying at high altitudes, where oxygen is limited. Ivy’s recently published study sheds light on how much songbirds’ bodies change seasonally. “When they get ready to migrate, their body changes, and they are now optimized to move oxygen to their flight muscle,” she says.

The study compared how six species of songbirds (blackpoll warbler, myrtle yellow-rumped warbler, hermit thrush, warbling vireo, red-eyed vireo and Swainson’s thrush) transport oxygen through their body during migratory and non-migratory seasons. It shows how birds are like magical shapeshifters, able to adjust their breathing patterns and change the size of their muscle fibres.

Ivy analyzed birds flying in the university’s hypobaric climactic wind tunnel, one of only two in the world, which mimics flight at high altitude conditions. “Not only can we change the pressure, but we can adjust temperature, humidity and wind speed. We can simulate anything,” Ivy says.

She found that myrtle yellow-rumped warblers performed especially well in high altitude conditions, reaching up to 4,000 metres — almost half the altitude of a commercial jet. Though they didn’t stay that high for long, they were able to fly at 3,000 metres for over an hour. Analysis of their seasonal physiology revealed that the changes they underwent allowed them to fly in a low oxygen environment with little effect.

Not all birds performed equally in the wind tunnel. The hermit thrush could not fly higher than 3,000 metres and exhibited fewer seasonal changes. Whether that puts the hermit thrush at a disadvantage in terms of climate change remains to be investigated. Yet what is certain is that not only do migration strategies vary among songbirds, but the seasonal changes to their bodies that enable their colossal endurance flights are nothing short of amazing.


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This story is from the March/April 2024 Issue

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