Nature Notes

September is the start of hawk-watching season. It’s not just for birders and folks with a special interest in hawks. Anyone can keep an eye to the sky – and on branches in the woods – in hopes of seeing south-bound broad-winged hawks (Buteo platypterus) this month, or other migrating or resident hawks.

What’s so special about broad-winged hawks? As they migrate south, they form large flocks that ride upward in rising warm air currents, forming “kettles” that can be a spectacular sight in the sky, with many hawks circling inside a current. In this way, the hawks use energy from the environment – in rising, expanding air that has been heated by ground warmed by sunlight – to power their flight. They typically fly to the bottom of a rising current (known as a thermal), ride it upward as they circle, and then take off near the top of the current and glide, soaring for quite a distance without having to flap their wings. Then they do the same with another rising current. This kind of soaring takes them quickly and efficiently on their way in their travels. They also use updrafts along ridges, where winds are forced upward by the shape of the land. And of course, their broad wings help them soar.

Broad-winged hawks (“broad-wings”) aren’t the only birds that use rising air currents. You might notice our familiar red-tailed hawks (“red-tails,” Buteo jamaicensis) circling in the sky. Turkey vultures (Cathartes aura) also use rising air currents to stay aloft in their daily searches for carrion.

What makes broad-wings different is that, unlike most other birds of prey, they migrate south in huge flocks. They can number in the hundreds or even the thousands. Hard to believe? Look, for example, at numbers reported in past years from a nearby fall hawk watch. Here are the largest numbers of broad-winged hawks counted on a single day at Mt. Wachusett: 7,981 (9/21/22), 1,902 (9/13/21), 3,898 (9/18/2020)*.

Locally, you might spot smaller numbers of hawks swirling upward in a kettle. Look up, especially if you hear something that sounds like it might be the cry of a hawk. Best times for seeing migrating broad-wings are usually around the second and third weeks of September. Kettles have sometimes been seen at MacCallum Wildlife Management Area, near the Mass Wildlife Headquarters (Westborough).

Look for hawks not only in the sky, but also in trees in local woods. Broad-winged hawks are forest birds. They summer and breed throughout the eastern U.S., including our area, and in southern Canada. They tend to hunt not so much from the air, as red-tails might do, but by perching on branches within the forest and watching for prey on the ground. They take mice, toads, frogs, shrews, chipmunks, snakes, and also birds and insects such as dragonflies. Red-tails also perch and watch, but you’ll typically notice these larger hawks sitting high up on top of something – a pole, post, or treetop.

Other hawks that you might see in the woods – and near birdfeeders – include two that specialize in hunting birds. Some Cooper’s hawks (Astur cooperi) are residents in our area, and some migrate. Sharp-shinned hawks (Accipiter striatus) are similar-looking but smaller. They typically appear in our area as they pass through on their fall and spring migrations.

You can listen, as well as look for hawks. Their sounds can tip you off to the presence of broad-wings, red-tails, or others such as red-shouldered hawks (Buteo lineatus), which look quite similar to broad-wings but have a different call. If you hear a flock of crows or blue jays making an excited racket, look around for a hawk that might have alarmed them.

When are good times for seeing migrating hawks (other than broad-wings), which usually travel alone or in small groups? Peak times locally are later in fall: very late October for red-tails and red-shouldered hawks, late September to mid-October for Cooper’s hawks and sharp-shinned hawks. Watch also for migrating turkey vultures, ospreys, bald eagles, and American kestrels. Local hilltops can be good viewing places.

Broad-wings migrate to wintering grounds in the forests of Central America and northern South America. They return to North American breeding grounds in spring, peaking in mid- to late April in our area. They migrate earlier in fall and later in spring than other birds of prey. Why? Possibly because broad-wings hunt cold-blooded prey (toads, frogs, snakes) more than other birds of prey do. Broad-wings migrate during the day and overland because that’s when and where thermals form. They avoid crossing large bodies of water, where thermals don’t form. When they travel, broad-wings spend about 40 days migrating.

How are broad-wings doing? Populations have increased slightly over the past 50 years. One reason may be the re-growth of forests in the northeastern U.S. over that period.

The usual hawk-watching spots in central Massachusetts include Mt. Wachusett (Princeton, Westminster), Mt. Watatic (Ashburnham, Ashby), and Barre Falls Dam (Barre Falls Dam recreation area off of Route 62 in Hubbardston).

Enjoy the season!

*Many thanks to Worcester County’s Forbush Bird Club for the hawk count numbers provided in its publication, The Chickadee: Journal of Worcester County Ornithology, volumes 90-92.