Diets dictate which birds go - or stay

Every fall, migratory birds set out on journeys dictated largely by their diets. Insectivores such as swallows and purple martins travel thousands of miles to ensure continued access to flying insects. Hummingbirds go where flowers are in bloom all year long. And orioles wing southward for a ready supply of fresh fruit. As winter descends in the north, these foods disappear, and so do the birds that depend on them.

Many of the colorful warblers, brilliant scarlet tanagers and bobolinks, might travel to South America before settling in. Eagles head for open water, which might be only as far away as Wabasha, Minn., and hawks travel to areas with a reliable, above-ground rodent supply.

More than 90 percent of the bird species we enjoy in spring and summer are on their way to areas where they'll live and forage for the next six months. From Mississippi to Mexico, from Belize to Brazil, our summer birds will soon settle in among those area's year-round residents.

Most of our Northern Hemisphere birds leave before they ever experience winter and its food scarcity. Their genes told them in August to start getting ready, and then environmental cues suggest when it's time to leave. This all is triggered by changing day length: When days start getting shorter, migratory birds start their migration countdown.

Tropics bound

The Baltimore orioles you feed each spring and summer are now flying as far south as Colombia and Ecuador to feed from fruit-laden shrubs and trees. The handsome rose-breasted grosbeak is a welcome sight to folks in the West Indies and Central America.

Our Eastern bluebirds are heading for Southern states, although some won't leave at all, if they can find enough water and berries to survive the winter. Some of our robins end up as far away as Guatemala, others move only a few hundred miles and increasing numbers stay behind to tough it out all winter.

Those acrobatic barn swallows are now chasing insects in Central and South America. Purple martins are settling down in Brazil, and tree swallows are free flying in northern South America and Trinidad.

Most woodpeckers don't migrate, but yellow-bellied sapsuckers do, with males traveling several hundred miles south and females traveling even farther, to Gulf states or the tropics.

Winter standbys

Even though most of our summer birds have left the area, we can enjoy watching the birds that stay through the winter. Goldfinches are still out there, but they're hiding in plain sight after molting into duller feather coats, eagerly dining on seed heads.

There are the white-breasted nuthatches, the busy chickadees and the bullying blue jays searching for insects or raiding their own caches of seeds and nuts. The sight of a pair of cardinals feeding on the ground brightens even the gloomiest day. And then there are birds like the dark-eyed junco, which migrates down from the north to spend the winter in parks and gardens, foraging on top of the snow for seeds.