As evenings become cooler in late August and early September, the southward migration of the Common Nighthawk begins. It’s a process you can miss entirely unless you know a bit about it. The birds move silently overhead at dusk, often only a few at a time, occasionally in large groups numbering in the hundreds or even thousands. The size of a robin, a nighthawk is somewhat slimmer in contour and appears uniformly dark in coloration, with long, pointed wings, somewhat like those of a falcon. A narrow white band, about two thirds of the way out on each wing, is a prominent field mark, easily seen with binoculars. During migration the birds fly well above the tree-tops, often gliding with raised wings, sometimes at heights of two hundred feet or more. They seem to seek out river valleys to follow as they move toward the south.
I agree with Yogi Berra’s comment that “You can observe a lot just by watching,” but in the case of nighthawk migration, you need to know where and when to look! To see them flying over, you should seek an open expanse with a wide view of sky above. A tower or similarly elevated observation point provides an advantage, but any large field, such as the upper meadow in Nahanton Park or the raised landfill in Millennium Park, will do. Large flights begin around August 15 and usually end by September 10 . In most years, numbers reach their peak on or about the 26th of August, but there are still a few stragglers through the end of September. A few birds can be seen moving by in daytime, but the largest flights occur within two hours of sunset, with highest numbers just at dusk. Should they encounter flying insects en route, they will detour to chase after them, swinging and swooping about erratically with deep wing beats. Such activity resembles bat flight, perhaps the reason some people call them “bullbats.”
For a few memorable moments on an August evening years ago, just at twilight, I was surrounded by hundreds of these birds dipping and swirling close to the ground. They had discovered a cloud of insects swarming over the field I had entered and interrupted their migration flight to drop down for a feast. In the early summer months, during breeding season, they’re quite noisy, and most city dwellers know their short, buzzing call as they circle overhead at dusk. Fans at Fenway Park can readily hear their calls above the din as they maneuver around lights, snatching out of the air the insects attracted there. On that late August evening, however, they moved in ghostly silence, their forms barely visible above the darkened field. After a short while, they disappeared over the horizon to resume their journey, and the air was suddenly empty.
Despite its name, the bird is not really a hawk in the true sense. It is a close cousin of the Whip-poor-will or the Chuck-will’s Widow, all three in a category referred to as “Goatsuckers.” This name came from the odd belief that these birds were able to steal milk from the udders of she-goats! Because it has a crepuscular lifestyle—“hawking” for insects in the sky before dawn and at dusk, and roosting unseen on a tree limb during the day—you are not likely to find a Nighthawk close at hand. Its scientific name is “Chordeiles minor,” the first term based on two Greek words translated as “evening traveler.”
Here in Massachusetts , the Common Nighthawk is now somewhat less “common” than in the past. Formerly, it nested on dry, open ground in areas scattered through the countryside and it was present across the entire state. With replacement of farmlands by growing forests, numbers have dropped off rapidly and the species is now found chiefly only in large cities, often nesting on flat rooftops in the absence of its usual terrain. Counts of the numbers of nighthawks migrating past several points throughout the state have been undertaken over the past two decades, and although one can challenge the accuracy of this method of sampling, it is the only means available to assess the size of the population. Reports from this year’s counts so far have been low—not everywhere—but low enough in total to increase our concern about the bird’s status in the state and in areas to the north. I would be interested to know if other Newton birders agree with my impression that the nighthawk in recent years has become scarcer in the skies over our city. If true, what a pity!