Fall 1998

[TEXT ARCHIVE WEB-PUBLISHED MARCH 2002.
ORIGINAL PRINT PUBLICATION DATE: FALL 1998.]

Broad-winged Hawk: Ride the autumn thermals

By Sheryl De Vore

The flight begins in September. First one, then two, then 10 or 20 and soon, a kettle of 200 broad-winged hawks (Buteo platypterus) ply the sky. They circle and ride the thermals created by hot air rising over sun-warmed patches of land. Rising as high as they can on one thermal, they then glide from the top of the air column to the base of another, rising again into another whirl of southward movement.

Though solitary nesters, broad-winged hawks prefer a company of hundreds during migration. And humans who look to the sky from mid-to-late September can witness one of nature's most fascinating displays. An average of some 4,000 broad-wings migrate through Chicago Wilderness each fall, in groups of hundreds or more.

Lake Michigan, the Des Plaines River, and other bodies of water serve as navigational tools for these small, broad-winged birds of prey with dark brown backs, light barred breasts, and black and white tail bands.

Glacial remnants such as ridges and moraines at areas such as the Blackwell Forest Preserve in DuPage County and Glacial Park in McHenry County help create updrafts that lift the broad-wings up to the thermals.

These hawks are coming from their northern breeding grounds in Michigan and Canada. Some also nested right here in the Chicago Wilderness area. For example, birders observed two young broad-winged hawks in a nest in south Cook County in 1995. The same year, a plant surveyor heard the shrieking two-syllable courtship cry of the broad-winged hawk all summer at Ryerson Woods in Lake County. Broad-winged hawk nests have also been discovered within the past 10 years in Will, DuPage, and McHenry Counties.

This uncommon Illinois breeder will only nest in heavily wooded areas. During courtship, the pair soars and swoops above the woodlands. Then a small stick nest is built in the crotch of a tree.

The female lays two to four eggs, then incubates them for 31 days. Mammals, primarily chipmunks, as well as shrews, voles, frogs, lizards, and young birds serve as broad-winged food in summer. When the cool winds come, the hawks take wing and fly as far south as Brazil where they dine on insects, lizards, and frogs.

One of the premiere spots for watching broad-wings during fall migration is at Mt. Hoy in DuPage County. This clay-capped landfill rises 150 feet above the Blackwell Forest Preserve, 30 miles west of downtown Chicago. The hawks funnel in between the DuPage River on the west and the moraine ridges east. Nearly 1,000 broad-winged hawks soared in kettles over Mt. Hoy one recent September day.

Illinois Beach State Park along Lake Michigan in Lake County and Glacial Park in McHenry County are two other good spots for watching broad-winged hawks during migration. Birders find the highest point at these parks where they sit for several hours watching the sky.

The broad-winged hawk flight reaches its peak the last week in September. Migrating hawks typically fly during the mid-morning hours, and strong winds encourage their flights.

Local birding groups sponsor free hawk watching outings this time of year. Call an area nature center to find out if a hawk watch is scheduled near you. Or just pick a day with strong winds and bring your lawn chair and a thermos of liquid warmth up to one of the mentioned areas or any high point near a body of water. Then wait for naturešs spectacular free show to begin.