Fall migration: How is it different from spring?

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If you pay attention to birds, you will have noticed that fall migration is not just spring migration in reverse. These two annual journeys reflect very different goals from a bird’s point of view, and present different challenges to the migrants as well as to our volunteers.

Chestnut-sided Warbler in Spring. Photo by US Fish and Wildlife Service Headquarters.
Chestnut-sided Warbler in spring. Photo by US Fish and Wildlife Service Headquarters.

Imagine you are a Chestnut-sided Warbler –  one of the roughly 350 species in North America that undergo long-distance migrations. You spend the winter in a sultry Central American forest. But when spring comes to the northern hemisphere, you need to get to your northerly breeding habitat, find a mate and hatch your young at the precise moment your preferred insect food becomes abundantly available. You need to get where you’re going in a hurry. You also need to look and sound your best to the opposite sex. When millions of birds pursue this mission at once, the result is a rapid, intense, colourful and noisy northward migration.

As fall approaches, temperatures cool and insects are harder to find. You need to move south, but there is no pressing agenda to fulfill when you arrive. You can take your time, lingering wherever you find food or other resources along the way. Following a different route than the one you took used in spring might help you conserve energy by taking advantage of wind patterns.  Flashy feathers and tuneful songs are no longer of use. Thus fall migration is a slow trickle of birds, less focussed and more subdued.

Chestnut-sided Warbler in fall. Photo by Andy Reago & Chrissy McClarren.
Chestnut-sided Warbler in fall. Photo by Andy Reago & Chrissy McClarren.

Our volunteers patrol the streets of Ottawa looking for birds that have collided with windows during both migrations. What we observe depends on the season.

In fall, we find birds gradually over a longer period, rather than in short bursts. We see a lot of young birds that just hatched over the summer and are migrating for the first time in their lives. Unfortunately when we find them, it’s because this maiden journey has been interrupted by a window strike. However, perhaps because of their youth, we find that a higher proportion of these birds survive their impacts than they do in spring. As a result, we have to perform a lot of rescues and our drivers are busy making lots of trips to the Wild Bird Care Centre.  Another challenge is that the birds are no longer in their breeding plumage, so identifying them is a bit trickier!

Whether it’s spring or fall, migratory birds face a long and perilous journey. Their chances of survival improve when humans take steps to mitigate the dangers we have placed in their path. You can help by making your windows bird-safe. Please call 613-216-8999 if you find a bird that needs to be rescued and report any dead birds using our online form. Happy migration!

Photo Sources: 
Spring: U.S. Fish and Wildlife Service Headquarters (Chestnut-sided Warbler) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
Fall: By Andy Reago & Chrissy McClarren (Chestnut-sided Warbler) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

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