Bird migration is a hazardous business

On a single night in late September, the Cornell Lab of Ornithology estimated, 334 million birds flew over the United States on their way to winter homes.

To me that's a mind-boggling number — a third of a billion birds in the sky in the dark above cities and towns, forests and plains, lakes and rivers, mountains and valleys. And birds are moving overhead nearly every night in the autumn, sometimes in huge numbers, at other times only a trickle of birds. As the sun rises each morning, these multitudes of birds flutter down to rest and refuel for the next night's journey.

Late September was the peak of migration for many species of birds, but before and after that time other birds, hundreds of millions of them, passed overhead in similar journeys. Birds do this twice a year, in a rhythm so long established that we take it for granted: "Oh, there go the birds," we think in autumn. And, "Here come the birds," we think each spring.

Birds may take it for granted, too, since the urge to migrate is hard-wired into their brains. But migration is hazardous and full of dangers, and many birds perish along the way: Only about half of the birds that head out each fall will make it back in the spring. To make the round trip they must pass — twice — through a gantlet of dangers. Experience gained in previous migrations is a help, and so is luck. But birds face all sorts of threats that are outside their control.

Traveling alone

A young rose-breasted grosbeak, just three months old, will make the journey from Minnesota to the mountains of South America in the fall. Along the way the young bird will face exhaustion, hunger, predators, disease, pollution and natural disasters, like hurricanes, wildfires and floods. The grosbeak will have to avoid colliding with buildings, utility wires and other hazards. And its own lack of experience is a strike against it, since, like most songbirds, she'll travel alone, with only a mental map to guide her on her first trip.

On top of all this is a singular threat, almost always caused by humans: the loss of places to rest and refuel each day. These stopover sites are key to the survival of migrating species. Such a site might be a park on the shoreline of the Mississippi River, a grassy bluff in Duluth, a bushy backyard in St. Paul, or a shrubby peninsula in Chicago.

Key to survival

Bird scientists and conservationists are starting to regard these stopover sites as critical to migratory birds. Just as we count on finding cafes along the route on a road trip, birds rely on patches of habitat to provide food, water and places to rest along the way. Their trips in the fall may take days or even weeks, so these refueling stations are vital to survival.

In fact, the Cornell Lab of Ornithology and other organizations are focusing greater attention on stopover sites, many of which are threatened by human development and/or the destructive power of global climate change.

Chris Wood, who directs the lab's population studies, says that researchers are using huge databases like eBird to identify the most important areas for songbirds heading to the tropics.

"This data can guide conservation efforts to be more strategic and effective," he says.

We can help, too (see box). And making some changes in our own backyards could help a hungry and exhausted young bird survive to continue its long journey.

St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for a number of newspapers and magazines, can be reached at valwrites@comcast.net.

Create your own stopover site

Your yard can be a place for birds to rest and refuel during migration:

Plant trees and shrubs that provide food and shelter.

Provide a birdbath and/or dishes of clean water.

Avoid using pesticides on grass or plants.

Keep bird feeders filled with seeds, suet and nuts.

Leave plant stalks standing for seed eaters.

Alert birds to windows with UV-reflecting decals.

Keep cats indoors, especially during migration.

Going the distance

How far do rose-breasted grosbeaks travel? A bird that departs from Baudette, Minn., in the fall may travel as far south as Panama or northern South America, some 3,300 miles, one way.

Eye on migration

You can track bird migration by using two amazing free tools, one estimating migration night by night, the other depicting a bird's travel year.

BirdCast Migration Dashboard estimates the total number of birds migrating through your county on any given night (start here: birdcast.info/about).

And the Bird Migration Explorer allows users to enter a bird species, then watch its migration route over a year's time (start at: explorer.audubon.org).