Migrating birds settle in for spring

It’s here, the 10-week period each spring when migratory birds are on the wing, a major highlight on nature’s annual calendar.

Beginning in mid-March and stretching into June, the birds that departed last fall are now flying back in to reclaim territories or establish new ones. Millions of hummingbirds, orioles, warblers, flycatchers, grosbeaks and swallows are now stacking up along our lakeshores, in woodlands, in open spaces and, in some cases, at our feeders.

Spring migration starts with a trickle. In early March, red-winged blackbirds "filled my rural Freeborn County yard," reported reader Al Batt, a sign of migration's start. By early May, migration is in full swing, with birds filling the air with their songs, trills and chirps. Some three-fourths of the birds that nest in North America are migrants, and share habitats with our resident birds for half the year.

Once they arrive, they're in a rush: These birds need to nourish their bodies after their long flights, then establish a territory and find a mate quickly. Their overriding impulse is to raise a brood (or two) of young birds. That's hard-wired into their genetic code to ensure the survival of their species.

Sharing the resources

Contrary to what many believe, it isn't the approach of winter's cold that drives migrants to head south in the fall. They leave because of food — or, rather, the lack of it — and they're returning because of it. Insects will fuel their nestlings' growth and insects will soon be abundant. The two big items on the bird menu in spring and summer are fruits and insects (or, really, arthropods, a broader category that includes spiders and earthworms and other energy-laden items).

There's a rocky period each spring, especially for migrants in the vanguard, which suffer through cold snaps and late snowfalls. It's tough on our resident birds, too, the ones that stick around all winter. The foods that got them through the cold season, dried fruits on trees and shrubs and insects hibernating in tree bark, are becoming harder and harder to find.

But once insects begin to emerge or hatch, the living becomes easier. The Baltimore oriole singing from a treetop is fueled by a new crop of caterpillars in the tree canopy. Colorful warblers flitting from leaf to leaf are picking off insects with their tweezer-like beaks. A yellow-bellied sapsucker chips sap wells into tree bark to lick up the springtime flow. And ruby-throated hummingbirds rely on the sapsucker's sap "farms" (and the tiny insects they attract) while waiting for flowers to bloom.

You might look out one day in late April and see six or eight beautiful rose-breasted grosbeaks drop down onto your seed feeders. Indigo buntings are on a similar schedule, appearing at feeders and birdbaths in early May.

And then there are the birds that aren't attracted to our bird feeders, including insectivores like barn swallows and tree swallows, those agile avian athletes that snatch flying insects from the air. House wrens thrive on insects, as well, and begin to show up in late April (sometimes competing with bluebirds for nesting sites).

Now is a magical time to be watching for birds, wherever you are — you never know what might appear.

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

Migratory birds that winter in the tropics tend to arrive around the same date each year, varying by 10 days or fewer. Spurred on by changes in day length, they lift off in Central or South America with no way of knowing what the weather is like at their destination. They've been doing this for eons and their species has survived late cold spells and snowfalls.

But a major challenge is presented by our warming planet and its effect on all living things. Spring now is arriving several weeks earlier, leading to insects hatching earlier. And it’s that first burst of insect life that migratory birds have traditionally relied on for nourishment after long flights. Insects hatching earlier while birds arrive on their old schedule is fraying the web of life. This lack of synchronicity may mean there’s not enough food for birds to enter the breeding season in top form.