Fall Hawk Watching
Although fall hawk migration starts in August with small numbers of hawks already on the move, the best time for watching is the month of September. Thousands of hawks and their young that breed north of Massachusetts move through the state in significant concentrations at this time of year.
Most numerous is the broad-winged hawk, which at times can be seen in flocks, or kettles, of hundreds, occasionally thousands of birds, "boiling" high into the sky. The next most commonly seen September migrants are the feisty sharp-shinned hawk, American kestrel, osprey, northern harrier (marsh hawk), and turkey vulture.
Although the total number of migrating hawks begins to decline after mid-September, the variety improves by late September and early October when more of the larger, less common raptors are moving. These include the Cooper's, red-tailed, and red-shouldered hawks; golden and bald eagles, peregrine falcon, and merlin.
The fall migration continues through October and into November, with good opportunities to see northern goshawks, red-tailed hawks, red-shouldered hawks, and eagles, along with rough-legged hawks, northern harriers, and rarely, a gyrfalcon. These late migrants are often also found wintering in Massachusetts.
Many of the larger, less common hawks that migrate south in October and November return north during late February, March, and early April.
Prime Weather Conditions
In the fall, the best migration conditions typically occur the day of and up to two days after the arrival of a high-pressure system or cold front along with accompanying northwesterly winds. The cold, clear air riding over the warm earth on a sunny day facilitates the formation of thermals. These columns of warm air that rise high above the ground provide the lift that facilitates soaring for many migrating hawks.
With scarcely a wingbeat, sometimes hundreds of hawks together may circle together in these thermals, soaring up and up until the thermal has dissipates. These kettles of hawks, especially broad-wings, often seem to "boil up," sometimes to the limits of vision.
The hawks then use the altitude gained in this leisurely manner to glide quickly and directly towards the next thermal. When they "peel off" from the top of a high thermal, their gradual descent can cover miles before the birds seek another thermal to ride aloft.
Moderate to weak winds, generally under 20 mph, blowing anywhere out of the north, from northwest to northeast, are best for optimum migratory–activity, especially at inland hawk watching sites. The best coastal flights often occur on days with strong northwest winds. If the sky is overcast, but the wind is favorable (even when it’s rather stiff), watch sites on ridges tend to be more productive than those on isolated hills or monadnocks.
Don't be misled into thinking that hawks only move when the winds are clearly from the north. When poor weather has held up migrants, they will fly under less than ideal conditions. In 1980, the biggest flights seen throughout New England occurred on weak southeast winds! In this instance, upper atmospheric winds were actually favorable for migration even though this was not easily perceived from the ground.
Time of Day
On favorable days for migration hawks can be moving shortly after sunrise, if not earlier. Inland however one tends not to see as many birds in the early hours as later in the morning, although the earlier birds might be lower and afford better views.
Prime time is often from 8 am to 4 pm (EST), but good numbers can sometimes be seen before or after those hours.
In the fall, look for a site—a mountain, hill, ridge, open field, or sand dune—with a view to the north and stretching from the northwest to the northeast. Explore the site under favorable weather conditions during peak season, to give the location a fair test. Also, be sure to regularly scan the sky with good binoculars.
Don't be disappointed if your site doesn’t seem productive the first day you try. Hawk flight paths are determined by a combination of weather and geography over thousands of miles, so they tend to be somewhat irregular.