Millions of hawks, other raptors fill autumn sky

In late September near Veracruz, Mexico, a "river of raptors" funnels over a narrow coastal plain between sea and mountain on its way to Central and South America. As many as five to six million hawks, falcons, kites and vultures stream overhead within just a few days. It is one of the great natural spectacles on the planet.

The river is stocked primarily with three species: Broad-winged Hawk, Hawk and Turkey Vulture. Smaller numbers of other species join them, including Mississippi Kite, Osprey, Peregrine Falcon, Cooper's Hawk and Sharp-shinned Hawk.

Broad-winged Hawks, or broadwings, are small "buteo" hawks, characterized by wide wings, thick torsos and relatively short tails. Broadwings have brown backs and brown-streaked bellies. Adults show a broad white tail band between dark stripes. A few nest in our area, but most spend the summer in the forests of Ontario, Quebec and the northeastern United States. Swainson's Hawks are larger buteos that nest out west.

Riding the thermal updrafts

A trickle of migrating birds in early September turns into a torrent by midmonth. The timing seems tied to weather conditions. Before the cool days of October, the hawks efficiently ride thermals and updrafts that are created when the sun heats the earth and easterly winds hit the mountains.

Richard "Rob" Bierregard teaches ornithology at UNC Charlotte. As he explained, hot air begins to rise as the earth warms in midmorning. A few birds find a thermal updraft, others follow and soon hundreds or even thousands form a "kettle" that rides the thermal thousands of feet into the sky. At the top, they set their wings and glide south or southwest along the currents. The system does not work over water, so the birds stay over land. In 2006, Bierregard was in the small town of Cardel outside Veracruz. With local hawk counters, he watched from a hotel rooftop as 24,000 Broad-winged Hawks soared by in one hour. More than 190,000 raptors went by that day, including 160,000 broadwings.

Why do these hawks flock in such large numbers? And, where does a group of that size find enough to eat? The birds travel together possibly because the easiest way to find a thermal is to follow another hawk. Regarding food, one theory is that the birds generally fast during the trip, other than a few insects they grab in the air. It seems unlikely they would find enough insects, amphibians and rodents at their evening roost sites. But skeptics say that the birds must eat something to maintain their strength throughout the trip.

One migration route for broadwings and other raptors is along the eastern ridgeline of the Appalachians. Every fall, observers at sites along the way submit daily bird counts to the Hawk Migration Association of North America (HMANA). Jim Keighton sets up a chair at Mahogany Rock, at Milepost 235 on the Blue Ridge Parkway. Keighton is a retired environmental educator and a weather buff. He enjoys the fact that "fall provides a special opportunity to watch raptors write on the wind." He also is aware that raptors are high on the food chain and therefore prime indicators of threats to our environment. So far, numbers show a stable broadwing population, despite ongoing deforestation and pesticide use at their winter grounds.

Pilot Mountain also offers good hawk viewing. Ramona Snavely discovered a kettle there in 1973 and began monitoring activity a year later. Toby Gordon has been counting at the pinnacle since 1991. He has observed how some hawks move off the ridge toward Pilot Mountain. "It is anyone's guess as to why," he said. "But perhaps the birds think the pinnacle is an extension of the ridge." A typical fall count is 2,000-4,000 birds. But large kettles occasionally occur. On one day in 1993, 10,800 broadwings passed by. Go to www.hawkcount.org to see data from Pilot Mountain and other watch sites.

This year, local hawk counters will be at Pilot Mountain during the last two weeks of September. Observers are always ready to share information, but the Audubon Society of Forsyth County has scheduled Sept. 20 and 21 as public education days at the pinnacle. Volunteer counters are welcome. Good eyes and binoculars are more important than experience.

■ Bird's-Eye View is a joint column by Ron Morris and Phil Dickinson. Today's column was written by Dickinson. Dickinson is a legal writer. He has been an active birder for 15 years, and is a past president of the Audubon Society of Forsyth County and chairs the conservation committee. Morris retired after 24 years as curator at the N.C. Zoo. He has studied birds around the world and is currently the vice president of the Audubon Society of Forsyth County. If you have a birding question or story idea, write to Bird's-Eye View in care of Features, Winston-Salem Journal, P.O. Box 3159, Winston-Salem, N.C. 27101-3159, or send an e-mail to birding@wsjournal.com. Please type "birds" in the subject line.