Raptors on the move, taking advantage of thermals

It’s that time of year again – birders are talking about kettles, updrafts, thermals and cold fronts. Raptors are on the move.

The jargon of migration isn’t hard to decipher once you get a mental picture of what it represents. Raptors must expend more energy than small songbirds to stay aloft, so they take advantage of whatever air turbulence they can find. This means they migrate during the day, when such turbulence is generally more pronounced. They are quick to take advantage of these conditions:

Thermals are circulating columns of warm air that rise when the sun heats the earth’s surface. Once a raptor – such as a broad-winged hawk, which utilizes thermals heavily -finds such a column, it sets its wings and simply allows this invisible escalator to carry it a mile or more into the sky. This can happen amazingly quickly; in seconds the birds will be almost out of sight. As the top of the thermal dissipates, the bird simply glides away into the distance, having achieved ample altitude so that it doesn’t have to flap its wings for quite awhile. If it is lucky, it finds another thermal to catch as it nears the ground – and up it circles again.

Thermals may attract many raptors, forming what birders have coined a “kettle” of hawks – so called because the rising birds resemble the steam rising above boiling water.

Birds of prey also utilize updrafts – airflow that is deflected up and over mountain ridges. These may come in handy on cloudy days, when the sun is unable to create thermals. Likewise, certain weather conditions are more conducive to easy migration – or, at least, to directing the birds to where we can see them. The passage of a cold front and the ensuing northwest winds have traditionally produced the highest counts of hawks at certain lookouts.

The raptors of Maine and northeastern Canada that we can expect to see on migration are: sharp-shinned hawks, Cooper’s hawks, American kestrels, merlins, peregrine falcons, red-tailed hawks, red-shouldered hawks, broad-winged hawks, osprey, northern harriers, and goshawks. Bald eagles are seen and counted, but they are not thought to be migrating long distances; most stay for the winter.

These birds undertake amazing journeys twice in one year, and it is truly a test of their stamina and strength. When you see a migrating hawk or falcon, wish them luck. In today’s world, they sorely need it.

Learn more about raptor migration by coming to the Fields Pond Nature Center on Wednesday, Sept. 17, at 7:30 p.m. Penobscot Valley Chapter president Jerry Smith will unveil some of the mysteries of hawk migration, provide clues to identify migrating raptors, and recommend great local hawk-watching hotspots. The fee is $5 for Maine Audubon members, $6 for nonmembers. To register or for directions, call the Center at 989-2591.

Chris Corio, a volunteer at Fields Pond Audubon Center in Holden, can be reached at fieldspond@juno.com