|A red shouldered hawk high in the branches.|
Each spring and autumn, as the twice-yearly spectacle of bird migration plays itself out across the North American continent, hundreds of thousands of people make a migration of their own. They congregate on windy mountaintops and lonely beaches, on grassy hills near suburban shopping malls, in rickety fire towers and on bluffs overlooking the Great Lakes or Pacific Ocean.
They are hawk-watchers, and their ranks are growing every year. Just as birding is enjoying an unprecedented boom in interest, so this variant on the sport is experiencing a groundswell, as more and more people discover the excitement of watching raptors in the wild.
Traditionally, hawk-watching is an autumn activity, although a number of spectacular spring migration points have been found. Though it has also traditionally been an eastern sport, hawk-watching in the West is gaining popularity, with several important sites the Marin Headlands by the Golden Gate Bridge in San Francisco, for instance, or the Grand Canyon in Arizona-as standouts.
Hawk-watching takes advantage of the fact that hawks follow the path of least resistance on their long flights north and south. That often means following mountain ranges, which provide steady updrafts as prevailing winds are deflected. In the West, mountain ranges can also provide a passage around inhospitable deserts, as happens in the Goshute Mountains of Nevada. Many raptor species tend to follow the ocean rather than ridges; for these birds, like sharpshinned hawks and falcons, bottlenecks along the coast are the places to watch. At Cape May, New Jersey, tens of thousands of hawks are funneled to the end of the peninsula that juts far out into Delaware Bay.
In spring, hawks catch southerly winds and migrate north across a broad front, avoiding the coast and inland ridges. Consequently, most of the autumn locations produce few hawks in spring. Those birds traveling east of the Mississippi, however, must contend with the Great Lakes, which form an enormous east-west barrier. To avoid crossing large bodies of water, many hawks turn along the lake shores, piling up in astounding numbers. Hawkwatches like Braddock Bay and Derby Hill in New York, on the shores of Lake Ontario, may tally more than forty thousand hawks in a single season.
Weather and Hawk Flights
More than sixty years of observations have shown that weather is the single biggest force affecting hawk migration. In autumn, the best conditions generally follow the passage of cold frontal systems, which produce blustery north or northwest winds for a day or two following the frontal passage. The sudden drop in temperature may spur the birds south, but the winds themselves deflected upward by mountain ridges are probably the biggest reason for the heavy flights, since they allow the hawks to glide for long distances with little effort.
As the cold front moves east, high pressure builds in behind it. The wind drops as the high passes overhead, but in the days that follow, the winds pick up again, this time out of the south or southwest. Hawk will use these breezes as well, although they must, naturally, fly on the south side of the ridge to take advantage of them. Depending on their location, most lookouts experience their heaviest flights on either northerly or southerly winds, but rarely both.
Some hawks are more dependent on weather conditions than others. Accipiters, falcons, and the larger buteos seem to need a stiff wind to get them moving, while northern harriers apparently do not. Broad-winged hawks are perhaps the least affected by wind conditions, moving from thermal to thermal with little regard to following ridges, and often traveling on hazy, almost windless days, or days when the wind is from the"wrong" quarter, such as southeast. Consequently, the bulk of the broadwings flight skips the mountains, traveling cross-country on thermals, and whether or not their path intersects a hawkwatch is a matter of luck.
In spring, ideal weather conditions are completely different. The days immediately before a frontal passage, not after, are the prime time, with gentle south winds and a low-pressure system approaching from the west. In either season, rain, snow, or fog generally means dismal counts.
Details mentioned in this article were accurate at the time of publication