Agility on the wing
Why versatile, agile Northern Harriers are able to migrate differently than all other hawks
Published: August 21, 2009
|I've seen many raptor spectacles involving Broad-winged Hawks, American Kestrels, and other common birds. One of my most memorable sightings, however, occurred with a species not often associated with the word spectacle.|
Shortly after dawn on a September morning at Cape May Point, New Jersey, a dozen Northern Harriers circled up a few hundred feet above the beach and then headed across Delaware Bay toward Delaware, 13 miles to the southwest. Because harriers usually aren't so gregarious, the scene left a lasting impression on me.
Northern Harriers migrate differently from other hawks. They are one of the most versatile and agile of raptor migrants in North America. They do it all: soar high in thermals, glide in ridge lift, fly early and late in the day when thermals are weak or absent, cross water, and resort to powered (flapping) flight when updrafts are not available.
Harriers have the ability to migrate long distances or not to migrate at all. They can fly as high as Swainson's Hawks, using thermals at 4,000 feet above the ground, or they can skim the tops of sand dunes or cut cornfields.
The ability to soar and glide or flap is key to their versatility. As the harriers I saw leaving New Jersey proved, water barriers are no impediment to the species. Studies I conducted at Cape May Point and Whitefish Point in Michigan showed that the birds are not reluctant to cross 13 to 20 miles of open water.
While Broad-winged, Red-tailed, and Sharp-shinned Hawks fly mostly around large lakes, bays, and sounds, harriers will fly more than 50 miles across water. They cross the Great Lakes as well as portions of the Gulf of Mexico and the Atlantic Ocean. We know this because observers sometimes see the birds arriving from water-crossing flights.
Birders also regularly report small numbers of harriers in the Bahamas, Cuba, and the Dominican Republic and on many other Caribbean islands. The birds don't breed there, so they must migrate from the mainland.
The ability to cross water is related to the harrier's flight morphology. Better than any other North American raptor, harriers can soar in thermals and use powered flight for extended periods of time. In at least a few instances, birds have been recorded flying, presumably migrating, in the dark when thermals aren't available.
I am not surprised because I have seen many harriers flying in the gray light of dawn and well after sunset.
If you observe a harrier migrating with Broad-winged or Red-tailed Hawks, watch as the birds glide between thermals. The hawks will glide faster because they have relatively shorter and wider wings, but they will also sink quicker than harriers, which weigh less and have longer wings.
Harriers may have the longest seasonal migrations among North American raptors. From August into December, birds are moving south. They appear again in February flying north on warm fronts and continue migrating into May. Therefore, migrants can be seen in some places during eight months of the year.
Young birds tend to migrate earlier in fall and later in spring than adults. The differential migration is similar to that of American Kestrels. Adult males, which are sometimes known as gray ghosts due to their plumage, are seen most often in late fall, and they winter farther north than immature birds or adult females.
The migration pathways of harriers are spread broadly across our continent. The greatest concentration during a season at a single site totals fewer than 2,000 individuals -- an amazingly small number, considering that the harrier population is about 1.3 million.
Viewing raptor migration first-hand is the best way to appreciate the unique flight behaviors of harriers. When you watch, compare them with other raptors, and you will quickly recognize their versatility and agility.
Morphology: the structure and function of wings, body, and feathers.
|11 places to see harriers|
See a Google Map of all 11 harrier hotspots.
1 Braddock Bay Raptor Research, near Rochester, New York
Based at Braddock Bay State Park. Hawk counts conducted March through May.
2 Cape May Hawk Watch, Cape May, New Jersey
Based at Cape May Point State Park. Hawk counts conducted September through November by the Cape May Bird Observatory.
3 Derby Hill Bird Observatory, Mexico, New York
Located on the southeastern corner of Lake Ontario. Spring hawkwatch (March through May) averages 40,000 raptors each year.
4 Golden Gate Raptor Observatory, Golden Gate National Recreation Area, California
Located on Hawk Hill just west of the Golden Gate Bridge. Studies migrating birds of prey along the Pacific coast. Counts conducted in fall.
5 Goshute Mountains, near Wendover, Nevada
Raptor counts conducted since 1983 by HawkWatch International. Source of much of our knowledge of hawk migration in the West. Project runs from August 15 through November 5 each year.
6 Hawk Cliff Hawkwatch, Port Stanley, Ontario
Located on the northern coast of Lake Erie. Hawk counts conducted September through November.
7 Hawk Mountain Sanctuary, near Kempton, Pennsylvania
Prime location for viewing migrating birds of prey, averaging 20,000 birds each fall. Maintains the world's longest record of raptor populations.
8 Hawk Ridge Bird Observatory, Duluth, Minnesota
Located on the western edge of Lake Superior. Averages 94,000 hawks each fall, from mid-August through November.
9 Holiday Beach Migration Observatory, north shore of Lake Erie, near the Detroit River, Ontario
Formed in 1986 to promote the study and protection of migrating birds. Counts hawks from late August to early December.
10 Lighthouse Point Park, New Haven, Connecticut
Hawkwatch on the shore of Long Island Sound. As many as 15,000 raptors counted each fall.
11 Wellsville Mountains, Mendon, Utah
Raptor counts conducted since 1987 by HawkWatch International. Up to 5,600 birds of 17 species each fall. Project runs from August 27 through October 31.