Stacey Cole's Nature Talks: Migrating hawks fill glorious September skies
By STACEY COLE | September 23. 2016 7:22PM
Here in New England, September is considered by many bird watchers as the month of the hawk, for it is then hawk migration is at its peak. Hawks journey over many thousands of miles from their summer breeding grounds to their winter quarters. The broadwinged hawk is the most common of these raptors seen in New Hampshire.
Occasionally several hundred of them will gather in a flock, a picturesque sight indeed. A few species winter in Texas, Brazil and the West Indies. The red-shouldered hawk flies to Central Mexico, and the red-tailed to Panama. The northern harrier, formerly known as the marsh hawk, flies from Labrador to Columbia and the West Indies. The rather diminutive American kestrel (sparrow hawk) that we frequently see perched on nearby high wires all spring and summer ventures to South Chile.
Large flocks of hawks are seen most every year, but not always, for occasionally only a few appear. They will arrive either singly or in pairs on one horizon and disappear at another. When one does see a large flock, though, it is truly an exciting experience. I should also note that one does not always need a beautiful clear sky for hawk watching. During a light rain or on foggy days, hawks often migrate close to the ground, hunting as they go. In real rough weather they seem not to move at all, remaining huddled in trees for protection while awaiting a break in the weather.
As to how weather conditions can affect the timing of migrating birds, I turned to the Fish and Wildlife Service, Circular 16, entitled, “Migration of Birds — U.S. Department of The Interior.” It read: “It is almost impossible to discuss separately the effects of different weather factors on migration because barometric pressure, temperature, wind and other meteorological phenomena are very closely related. On the North American Continent, air masses generally proceed about 600 miles a day from west to east. These air masses vary in pressure, temperature, humidity and wind. The wind within these masses travels in either a clockwise (anticyclonic) or counterclockwise (cyclonic) direction. Cyclonic air masses contain relatively moist warm air with low barometric pressure centers (lows). Anticlyclonic air masses are characterized by dry cool air with high barometric pressure areas (highs). When these air masses meet a ‘front’ is formed and the rapidity with which this front moves through an area depends on the temperature and pressure gradient on either side of the front. An understanding of frontal systems, with their associated wind, temperature and humidity, is one of the keys to understanding when birds migrate.
“During fall migration, the best passage of migrants usually occurs 2 days after a cold front has gone through. That is, the low has passed and it is being followed by a high characterized by dropping temperatures, a rising barometer and clearing skies. During spring migration, weather conditions conducive to strong movements of birds are somewhat the opposite from those in the fall. Birds will move north on the warm sector of an incoming low.”
The few nighthawks that nested in New Hampshire left us in late August and some of the north-nesting shorebirds are now passing through on their way south. Most raptors will soon begin their movement to the south if they haven’t already.
During this month and into October, look to the skies as your day permits and spend a few moments watching for hawks. One September morning, while in Concord, I counted more than 500 hawks within a 15-minute period over the State House. They were mostly broad-winged, with an occasional red-tailed mixed in.
Several nature organizations have arranged times and locations for their members to participate in one or more days to hold what they refer to as a “Hawk Watch.” Usually non-members are welcome. It’s a good place to start.
Stacey Cole, Nature Talks columnist for more than 50 years, passed away in 2014. If readers have a favorite column written by Stacey that they would like to see reprinted, please drop a note to Jen Lord a firstname.lastname@example.org.