SEPTEMBER SKIES, I believe, are the most beautiful offered by any month of the year.

September, the month that possesses the autumnal equinox, tenders an abundance of bright blue canvases that serve as backdrop for my day dreaming. There is little, perhaps nothing, more picturesque than a hawk circling without apparent effort, as an overlay for such a resplendent background. Yes, September skies are favorite meeting places for migrating hawks.

Here in New England, September is considered by many bird watchers as the month of the hawk, for it is then hawk migration is at its peak. Hawks journey over many thousands of miles from their summer breeding grounds to their winter quarters. And many of them travel together. The broadwinged hawk, the most common of these raptors seen in New Hampshire, is apt to winter in Texas, Brazil and the West Indies. The red-shouldered flies to central Mexico, and the red-tailed to Panama. The northern harrier (formerly marsh hawk) flies from Labrador to Colombia and the West Indies. The rather diminutive American kestrel (formerly sparrow hawk) that we frequently see perched on nearby high wires during spring and summer, ventures to south Chile.

Some years only a few hawks will be seen, either singly or in pairs, arriving on one horizon, departing at another. To see a large flock, though, is truly exciting.

One does not always need a beautiful, clear sky for hawk watching. During light rain or on foggy days, hawks often migrate close to the ground, hunting as they go. In real rough weather, they seem not to move at all, remaining huddled in trees for protection while awaiting a break in the weather.

For many years, my late wife, Mildred, and I traveled to Mount Torn, near North Hampton, Mass. Near the summit there was a small knob known as Goat Peak, where an observation tower was located. This provided a panoramic view of a large section of the Connecticut River Valley. On a good day, a vast number of hawks suddenly appeared, occasionally flying close to the ground. On more than one of those trips, we counted as many as 1,500 hawks in less than an hour as they passed near that vantage point. During those years, others reported sighting many more.

Large numbers of hawks may be seen in unexpected places. For example: in Concord, within a 15-minute period one September morning, I counted more than 500 hawks circling above our state capitol building. A most unusual experience. Hawks in that flight were mostly broad-wings, with an occasional red-tailed mixed in. The birds circled round and round as they drifted higher and higher above the golden dome of the State House. The birds appeared completely unhurried as they circled, attaining a great height. Birders call that performance “kettling.”

After hawks gain enough height to suit them, they commence their travels southward, by riding the currents of heated air rising from below, known as thermals. Without beating a wing, they can travel for miles. I found an excellent description of thermal development in “Feathers in the Wind,” published by the Hawk Mountain Sanctuary Association, Route 2, Kempton, Pa.

“The generating force of thermals is sun-supplied heat. The story begins in early morning while the sun is still below the horizon. The cool night air has covered the ground with moisture and dew, and the valleys are blanketed with heavy ground fog almost to the saturation point. The sun slowly rises and soon its rays are heating and dispersing the moisture. As the sun climbs higher, its rays now strike the earth at right angles, creating maximum heating. In early morning, as in late afternoon, the sun's rays are at a very low angle, taking a longer path through the atmosphere. By sunset, thermals are generally poor. The rays pass through the air without heating appreciably. When they strike the earth, they are either absorbed or reflected, depending on the surface. For example, dark surfaces such as plowed fields will absorb more heat than a forested surface, which has a large area of moisture-producing vegetation with its accompanying cooling effect.

“The heated air expands and clings to the ground as the surrounding cool, heavier air holds it in place. This is much like bubbles on the bottom of a kettle before water reaches its boiling point. As the air continues to be heated, it expands and finally rises from the ground. Once risen, it is replaced by cooler air.

“The process continues with bubbles being formed and released, sometimes combining as they go aloft. When this occurs, the water vapor again reaches its saturation point and a cloud forms. The lift will continue as long as a thermal is supplied with energy and moisture from below.”
Stacey Cole's address is 529 W. Swanzey Road, Swanzey 03446.