Keep an eye out for waves of migratory birds returning to Georgia in April

Bird migration starts early

Spring migration actually kicked off in early February when purple martins started arriving from winter homes as far south as Peru for their nesting season.

In March, other songbird migrants began trickling in — Louisiana waterthrushes, Northern parula warblers, ovenbirds and more. Some non-songbird migrants also began showing up. The plaintive, evening calls of chuck-wills-widows and whip-poor-wills could be heard by late March, and everybody’s favorite, the ruby-throated hummingbird, began coming in.

But now, in April, the trickle will become a torrent. A few weeks ago, only a few thousand birds were arriving per day. But the pace is fast picking up: By late April, millions of migratory birds will be pouring in. The majority will be songbirds, most of them flying at night. (An exception is the ruby-throated hummingbird, which travels mostly by day.)

The advantages of flying at night

Flying at night has several advantages for migrating birds: The air is cooler and the darkness helps them avoid predators. Most avian migrants also use stars to navigate.

Their night flying, however, means that we can’t see these massive songbird waves winging just above our homes across Georgia. But there’s another way to detect them in real-time — by Birdcast (birdcast.org), a free online app developed by the Cornell Lab of Ornithology and its partners.

It uses weather radar and other powerful tools to detect and predict the numbers and flight directions of migrating birds aloft in Georgia and other areas. It provides data on birds’ migration intensity, speed, direction and altitude. For instance, during a 12-hour period beginning at 8 p.m. earlier this week, Birdcast showed that 435,000 birds crossed over DeKalb County, where I live.

A dangerous journey

It’s a wonder, though, that neotropical birds make it back at all. Migration is fraught with deadly dangers — hungry predators, light pollution, building collisions, starvation because of habitat loss and exhaustion.

The American Bird Conservancy estimates that this spring, more than 2 billion birds — including ruby-throated hummingbirds — returning from Latin America will fly more than 500 miles nonstop (as long as 18-22 hours) over the Gulf of Mexico to reach the Gulf Coast.

As they come in, they are exhausted and emaciated, badly in need of rest and refueling. After a few days, though, they’ll fan out to nesting grounds across the country, including Georgia, and Canada. Along the way, they’ll need more rest and refueling stops — forests, thickets, fields, wetlands. Unfortunately, such habitats are becoming fewer as development chews up thousands of acres each month.

Males, sporting their spiffy breeding plumage, typically arrive at spring nesting grounds a week or two before females to establish territories, which helps them lure mates. When the birds form breeding pairs, they’ll quickly commence mating and nest building.

Timing is everything: Over eons, migratory birds have keyed their return to when tons of caterpillars and other insects are devouring the tender, new foliage of trees and other vegetation. In turn, the adult birds will feed the insects to their babies, thus saving the trees from defoliation. Climate change, however, threatens to disrupt this age-old timing.

The incoming migrants will mix in with our year-round species — cardinals, bluebirds, chickadees and others, which have been nesting for several weeks now. The year-round species may be preparing to raise a second clutch by the time most spring migrants are starting on their first brood.

IN THE SKY: From David Dundee, retired Tellus Science Museum astronomer: The moon will be last quarter on Friday (April 10) and new on April 17. Over the next two weeks, the only planet visible is Jupiter, high in the west at dusk. Mercury, Mars, Venus and Saturn aren’t visible.

Charles Seabrook can be reached at Charles.seabrook@yahoo.com.