The Forecast Calls for Birds

Writer Bryan Pfeiffer looks for bird fallouts during Tropical Storm Irene. Photo by Ruth Einstein.

Songbirds pouring from the skies before dawn. Thousands of hawks gliding past a mountain summit. Rare oceanic birds blown in to shore. Birdwatching like this doesn’t necessarily begin when you go outside. It begins with a weather forecast the day before.

Weather can generate spectacular birding. Consider the spring fallout, when birds rain from the heavens. Fallout conditions occur when warm air from the south or southwest meets colder air to the north. The collision can produce fog, rain, and swirling winds – weather you might not consider suitable for birdwatching. But these conditions can cause countless birds – migrating north on tailwinds – to drop from migration and into view.

Topography can also be your partner. If they’re over water, migrants seek any port in a storm, which means they will pile up on islands and along peninsulas. When forced into urban areas, songbirds often move to the nearest patch of trees where they find cover and food, which is why Central Park in New York City and Mt. Auburn Cemetery in Boston are legendary spring birding destinations.

During spring fallouts I’ve seen trees glowing with dozens of warblers seeking shelter from wind and rain. I’ve encountered exhausted scarlet tanagers at my feet. And I’ve experienced 70 indigo buntings in a single thicket. So dense are birds during a genuine fallout that you can point your binoculars in most any direction to find something flitting or flying.

It pays to watch the weather in autumn as well. The right conditions for hawkwatching generally feature cold fronts with weak or moderate winds blowing from the north. Hawks move relatively effortlessly on those crisp days in September and October. They rise late morning with thermals of warmer air generated by autumn sun shining into valleys. After reaching sufficient elevation, hawks break out of their thermal and glide south on high tailwinds. Meanwhile, along the ocean shore, it’s fine to spend a fall day watching eiders, scoters, loons, grebes, gannets, and gulls. But if you want alcids, jeagers, shearwaters, and other odd ocean-going birds, grab your foul-weather gear and get out during a Nor’easter or other weather that generates on-shore winds pushing the rare birds closer to land.

It’s one thing to know the local forecast when heading afield, it’s another to “see” birds on the way. The National Weather Service’s Next Generation Weather Radar system, NEXRAD, is sensitive enough to detect birds, bats, and occasionally insects in flight. Many songbirds rise together to migrate after sunset, and they’re often dense enough to form distinctive radar patterns that have a different profile from those of clouds and rain. Migrating birds move faster than prevailing tailwinds, which means the radar patterns, when viewed over time in an animated loop, help confirm that you’re indeed looking at birds in the air and show you the direction of the flight.

Reading online radar images takes some training, but a few dedicated biologists are watching the radar and the skies, and alerting birders when migrants might be coming. Two websites to watch are Wood Creeper and the Radar Ornithology Laboratory at Clemson University. Visit their tutorials for lessons on radar and migration. A good source of radar data is Real-Time Weather Data.

Birdwatchers need not be slaves to weather – good or bad. Head out for birds any old morning this spring. But also realize that, at the very least, it pays to know which ways the wind blows.

Bryan Pfeiffer is an author, wildlife photographer, guide, and consulting naturalist who specializes in birds and insects. He lives in Montpelier, Vermont.


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