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Broad-winged hawk migration: kettles over New England in September

September

For one brief window centered on mid-September, broad-winged hawks pour out of New England in soaring flocks called kettles, hundreds and sometimes thousands boiling up one thermal at a time on their way to South America.

Why this time of year

This is the sharpest-timed spectacle in the Massachusetts bird year: the state's three record flights all fell between September 13 and 17, and it is extremely rare to see a broad-winged hawk here in winter, so the door closes fast.

How to notice it

  1. Pick a day on the heels of a cold front with northwest winds; prime hours are 8am to 4pm.
  2. The reliable show is a watch site: Wachusett Mountain in Princeton averages about 11,000 broad-wings a season, and Mount Watatic also hosts a fall watch.
  3. At home, check any wide mid-September sky when hawks are moving; a passing kettle looks like a slow swirl of specks climbing a thermal, worth a minute with binoculars.
  4. Watch one kettle work: birds circle up the thermal without flapping, then peel off the top and glide south to the next one.

Try this with kids: Count the hawks in one swirl before they peel off the top and glide away.

a kettle is a flock of hawks circling together in a rising column of warm air

Safety

  • September summits are exposed; bring sun cover and a layer for wind.

Sources

  • massaudubon.orgFall hawk migration begins in August and peaks in September; the most numerous hawk is the broad-winged hawk, at times seen in kettles of hundreds, occasionally thousands, boiling high into the sky; fall sites include Wachusett Mountain State Reservation and Mount Watatic Reservation; best conditions follow the passage of a cold front with northwesterly winds; hawks begin moving shortly after sunrise and prime time is 8am to 4pm.
  • massaudubon.orgEvery autumn during a brief window in mid-September, thousands of broad-winged hawks can be seen soaring in kettles as they head to Central and South America; among our longest-distance migrant hawks.
  • massaudubon.orgThe most abundant species by far is the broad-winged hawk, averaging 10,995 per year at the Wachusett watch; the largest Massachusetts flights were 20,106 on 9/13/83, 17,517 on 9/17/84, and 16,062 on 9/13/89.
  • audubon.orgMigrates in flocks called kettles; almost all individuals leave North America in fall, most to South America; during migration thousands can be seen along ridges when wind conditions are right.

In the guide for September

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