Photo by Jean Potter • A common nighthawk rests on a metal railing.

With September advancing on the calendar, I have been keeping an eye on the skies. For the most part, I focus on the upper branches of trees and feeders during the migration season, but I don’t forget the need to look skyward from time to time.

The reason? Well, that’s the best way to detect soaring raptors or flocks of migrating common nighthawks. The autumn sky is also a popular flyway for other birds, including chimney swifts and swallows.

So, what is a common nighthawk? First, this bird, despite what is implied by its name, is not a hawk. It’s also not strictly nocturnal. Particularly in the fall, nighthawks are active during daylight hours when engaged in catching winged insects. Outside of fall migration, these birds can often be observed over large parking lots or well-lit streets, snatching up insects swarming around the light poles.

The common nighthawk is one of three members of the nightjar family found in the region during the summer months. The other two nightjars are the whip-poor-will and chuck-will’s-widow, birds that produce their namesake vocalizations in the nocturnal hours. Both of these species migrate, but they don’t take the dramatic approach employed by nighthawks. Each fall, common nighthawks form large flocks, ranging in size from dozens to hundreds or even thousands of individuals, as they migrate south for the winter.

Early American naturalist and artist painted this dynamic scene of common nighthawks.

The whip-poor-will, after the common nighthawk, is the second most widespread member of its family to spend its breeding season in North America. The whip-poor-will ranges from southern Canada to the Gulf states. This bird also occurs in Arizona, New Mexico and southwestern Texas. The whip-poor-will favors habitat consisting of deciduous woodlands and the edges of forests.

All members of the nightjar family feed exclusively on insects that are caught on the wing. In this respect, the nightjars can be considered the nocturnal counterparts of the swallows. The nightjars have comparatively large, gaping mouths they use to scoop up flying insects. They also have large eyes, an adaptation to their nocturnal lifestyle.

Whip-poor-will numbers have been declining in the past few decades. These nocturnal birds frequent woodland edges, but they seem to be rather particular about such habitats. A forest that is too mature seems to hold little interest for them. Disturbed habitats, such as those created by logging, are acceptable to the birds once secondary growth begins. As this new growth matures, however, the whip-poor-will apparently abandons such territory. Because of these requirements, whip-poor-wills can be somewhat localized in their distribution and sometimes difficult to locate.

Photo by U.S. Fish and Wildlife Service • A common nighthawk finds a perch for a brief rest.

When I was a kid, one of my favorite summer activities was sitting on the front porch of my grandparents’ home and listening to the whip-poor-wills call after dark. I remember how the plaintive call would be repeated for long intervals before a passing automobile’s headlights might frighten the bird into silence. Then, after a brief pause, the “whip-poor-will” calls would, tentatively at first, begin again and continue throughout the night.

Today, I’m living in my grandparents’ old home, and the whip-poor-wills no longer call. I heard a single individual that called for a single evening back in May of 1997, but that was apparently a migrating bird that did not remain in the surrounding woodlands. The only member of the nightjar family that I dependably encounter at home these days is the common nighthawk, and then only during that narrow window of late summer and early autumn.

Unlike whips and chucks, the common nighthawk isn’t active only after dark, which makes it much easier to observe these birds. They look somewhat like swifts and swallows but are much larger. They are brownish-gray birds with pointed wings and forked tails. They are easily identified by distinctive white patches on the underside of their wings.

The nightjar, or Caprimulgidae, family of birds is also sometimes known as “goatsuckers.” There are almost 80 species of nightjars in the world. Less than 10 occur in North America. The common nighthawk, whip-poor-will and the chuck-will’s widow are neotropical migrants. While they breed in a wide range of territory in North America, they spend their winters in Central and South America. Like all nightjars, nighthawks feed almost exclusively on insects, which they catch on the wing.

Many of the common nighthawk’s relatives have been given descriptive names, such as long-trained nightjar, collared nightjar, spot-tailed nightjar, red-necked nightjar, golden nightjar, fiery-necked nightjar, swamp nightjar, pennant-winged nightjar, lyre-tailed nightjar, little nightjar, sickle-winged nightjar, rufous-bellied nighthawk, short-tailed nighthawk, sand-coloured nighthawk and least nighthawk.

So, keep looking skyward. The next flock of migrating common nighthawks may fly over your home. These flocks are usually on the move throughout September although they begin to appear as early as late August. They can also appear almost magically, as if out of thin air. First, observers may see one of two birds, then several, followed quickly by dozens or sometimes hundreds as they wheel and cavort in the skies overhead with impressive grace and agility. I’ve seen flocks that would easily number more than 500 birds in locations throughout the region, although flocks often number only a couple of dozen birds. The two flocks I’ve observed so far this migration season numbered about thirty and fifty birds, respectively.

Photo by Bryan Stevens • Rising clouds provide a backdrop for a flock of migrating nighthawks.