A long day's journey in flight

Now is one of the best times to watch for migrating birds swooping and diving overhead.

It's a bird, it's a plane - no, wait, it is a bird. But what kind? As winter approaches and flocks of birds leave your tree limbs for warmer climates, you may be wondering exactly what's swooping overhead.

Now is one of the best times to look for birds in the northern hemisphere, when birds migrate south to escape the cold and lack of food, says Steven J. Saffier, science associate of Audubon at Home, a bird group. "Generally, birds migrate in the spring [when they fly north to breed] and in the fall," he says.

As days grow shorter and temperatures drop, most birds know it's time to move on. Their food, which includes fruit and insects, runs out. Lakes and streams that supply food freeze over.

Not all birds migrate. Some, like the American dipper, find enough to eat to survive winter. But most birds take to the skies.

When they migrate, birds have to stop along the way to rest and refuel, sometimes for several days or weeks. This is a good time to see them. Ponds and lakeshores attract ducks, geese, and blue herons. Flower beds attract hummingbirds. Grain fields near harvest time will attract seed-eating birds such as American goldfinches or mourning doves. They also attract raptors, which go after rodents that eat the seeds.

"Most birds will not cross big bodies of water like oceans or the Great Lakes," says Greg Kaltenecker of the Idaho Bird Observatory. "So coastlines, especially peninsulas, are great places to see migrating birds."

Air currents called "thermals" play an important role in migration. "Many birds rely on warm currents of air that rise from the ground, called thermals, which propel them in their gliding flight," says Mr. Saffier.

These currents help keep birds airborne, so they don't have to exert as much energy on their long journeys. Many birds rely on thermals when they travel along common migration routes called "flyaways." Imagine a bird highway of sorts. There are four major flyaways in North America, with lots of branches. They include paths along the Atlantic Ocean, the Mississippi River, the central US, and the Pacific Ocean.

Some birds travel very far. The American goldfinch, for instance, spends summers in Canada and winters in the southern US.

When you're watching the skies, there are signs that can help you identify birds. You can assess a bird's "gis." This is a bird-watching term that stands for "general impression and shape." It originally was a military term used to identify aircraft. In bird-watch talk, it includes the bird's silhouette, wing angle and shape, flight pattern, and the way it moves and behaves. For instance, does the bird flap or glide? Does it have long wings sticking straight out or pointed wings that curve?

It's a good idea to have a bird book handy. And if you carry a notebook and pencil, you can sketch the way a bird flies and identify it later. Binoculars also help catch the details.

Many birds, including songbirds and some waterfowl, migrate at night, says Mr. Kaltenecker. "Listen for migrating geese or swans passing over on a clear night in late October," he says. But morning is the best time to see most birds. They stop to feed and rest after a night's journey. Some migrating birds include:

Bluebirds. When they migrate (not all do), they form loose flocks, as families leave together. They can look like butterflies when they flutter their wings in slow, deep beats. They also are known to fly lopsided!

Canada geese fly in a "V" shape. They have black heads and necks and white chin straps.

The great blue heron has a 7-foot wing span and flies with its long legs behind it. It migrates alone or in groups up to 100.

One of the most interesting migrating birds is the rufous hummingbird. It flies the farthest of all hummingbirds, making a yearly trip between Mexico and the Pacific Northwest and Alaska. It may travel as far as 2,000 miles. Hummingbirds rely on nectar from flowers, so they move to climates where they can find flowering plants. During its journey, the hummingbird makes rest stops. It claims a plot of nectar-filled flowers and guards it, chasing away other birds, butterflies, and bees.

Raptors are birds of prey and include hawks, falcons,and eagles. Each has its own pattern of flapping and gliding. They tend to be stronger and larger than other birds. Sharp-shinned hawks, Cooper's hawks, and northern goshawks typically make several wing flaps followed by a glide. Peregrinefalcons are the size of crows and have sharp sickle-shaped wings. They dive after their prey, usually other birds, and migrate alone.

The bald eagle can dive up to 100 miles per hour in quest of its favorite food, fish. It can carry up to eight pounds in its beak. Bald eagles are not bald, but have white feathers on their heads. The brown eagles flying with them are their young, whose white feathers haven't grown in yet. Eagles can soar for hours using wind currents and have a screechy cry.

The turkey vulture is a glider that rides air currents with so much skill that, sometimes, it doesn't even have to flap its wings. From the ground, it appears to have a black body and silvery gray feathers.

American kestrels are often seen hovering over country roads and fields looking for prey. They are smaller than falcons and fly by making several wing flaps followed by a long glide. The male bird has a rust-colored back and a head that's rust, blue, black, and white. Its wings are bluish-gray, dotted with black. The female has duller coloring.

Have fun with the birds this fall and keep your eyes on the skies!

Sources: National Audubon Society, Idaho Bird Observatory, Audubon at Home.