Brilliantly colored leaves are impressive, but I say migrating birds are fall's real signature event. Think about it: You may have to travel to find autumn foliage. But you can probably find a spot to observe migrating birds near where you live, if not right in your backyard. Every autumn, more than 5 billion birds migrate across North America, crossing the U.S. at rates of tens of millions a day.

Contrary to popular belief, birds migrate not because the weather becomes too cold, but because they run out of things to eat. With the coming of winter, insect life dies down, snow covers the ground, water freezes over: nature's cupboard is becoming bare. Birds that can find something to eat will frequently stay put, such as city pigeons or carrion-eating crows.

A sky full of Canadian geese at Wisconsin's Horicon National Wildlife Refuge. Photo Credit: Refuge Reporter

You hear a lot about 'flyways' the notion being that birds move in defined corridors, like traffic down a road. Traditionally, birders talked about four main flyways: Pacific, Central, Mississippi and Atlantic. Research indicates that this can be a misleading way to think about migration. Instead, imagine broad bands, like test patterns on a television, moving down the continent. Geographic features can funnel birds, narrowing the bands. Mountain chains the Cascades and Sierra Nevada, Rockies, and the Appalachians present barriers and also opportunities. Raptors coast the 'thermals' or (updrafts of warmer air) found along the ranges. South pointing peninsulas, such as New Jersey's Cape May, funnel birds in the autumn; just as a north pointing peninsulas funnel them in Spring. Birds moving down the coast find the land narrowing beneath them and they become concentrated at the peninsula's tip.

How do you find a good spot to observe the fall migration? Three words: habitat, habitat, and habitat. Birds will congregate where they can find something to eat and protection from predators. Believe it or not, autumn and spring birdwatching can be pretty good in New York City. But you won't find many birds along hectic Seventh Avenue. Instead, try the brushy areas of Central Park and the dearly preserved wetlands at the city's edge. (However, if you look up you may spot a hawk making its home in the cliff-like walls of skyscrapers.)

We've done a survey of good places to observe the fall bird migration. Some of these places are where birds will be passing through. Some are winter destinations, where they might be spending a few months. Here's an overview . . .