Hawk Watching Season
09-25-2007 - Fall is the best time of year to observe migrating hawks, which depend on certain weather conditions to ?fuel? their south-bound movements. So keeping an ear tuned to the weather forecast will provide a good clue as to when the best conditions exist for seeing migrating raptors, sometimes in great numbers.
 Unlike passerines, waterfowl, or shorebirds which utilize stopover habitats to build up fat reserves that power their migratory flights, raptors are top predators on a limited energy budget. So while the migrations of other groups of birds consist of long bouts of nearly continuous flapping, raptors avoid such strenuous exertion at all costs. Instead, they wait for conditions that create updrafts for lift, and winds that will blow them in the direction they wish to go.
Ideal hawk-watching conditions occur when a cold front passes through the region, bringing bright sunshine and cool, strong winds out of the northwest. As the sun warms the earth it creates thermals ? bubbles of warm air that rise like hot air balloons. To migrating hawks, thermals serve as elevators, giving them a free ride to the upper ?floors? of the atmosphere. When hawks locate a thermal, they soar in circles, spiraling upward, often to great heights. Frequently, many hawks will use the same thermal, swirling and criss-crossing together like a boiling pot of hawks ? a phenomenon known as a kettle. When they reach the upper levels of the thermal, hawks begin peeling off one by one on set wings, riding the northwest tailwind, sometime for miles, to the next thermal.
Hawks will also use deflective currents to gain lift on days with poor thermal activity. Deflective currents are simply strong winds that are deflected upward by topographic features such as mountains or cliffs. While these currents may not bring hawks to the great heights provided by thermals, they can sometimes provide better viewing conditions since the birds are not as high.
While most any open hilltop that affords a good, unobstructed view to the north and northwest could provide good looks at migrating hawks, two spots in Vermont seem to provide consistent results. In the Champlain Valley, Mount Philo State Park in Charlotte is a popular hawk watching destination that is frequented by experienced birders willing to share their knowledge. In the Connecticut River Valley, fall hawk watches have occurred regularly on Putney Mountain since 1987, and a core of volunteers now monitor migrating hawks nearly every day during the autumn season and report their results to the Hawk Migration Association of North America.
With the passage of several cold fronts last week, both of these sites witnessed remarkable movements of hawks. On Monday, Sept. 10, Mt. Philo observers counted nearly 3,200 hawks of 10 different species (3,006 of those were Broad-winged Hawks). Putney Mountain?s big day came on Sunday, Sept. 16, when they tallied 1,290 hawks of 6 species, including 1,213 Broad-wings. While the majority of Broad-winged Hawks are likely to our south now, the steady movement of migrating hawks will continue for the next month or more. So keep an eye on the weather, and when the conditions are right, head out to a hilltop or mountain summit near you.
Source: The Vermont Center for Ecostudies
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