This is the time to be looking for common nighthawks migrating south, especially in the couple of hours before dusk.
Nighthawks are one of my favorite species because of their aerial grace and agility and their habit of flying in loose groups, enabling one to see dozens or more at once. In flight, they superficially resemble small gulls in shape, but they are dark, fast-flying and show a conspicuous white bar on the flight feathers perpendicular to the wing.
At times, they will dart to one side or the other to snare insects much in the manner of bats. Last evening, I sat on my dock and counted nearly 100 heading south at about 200 feet altitude over a 45-minute period.
Nighthawks are not hawks at all but members of the family Caprimulgidae, which includes our whip-poor-will and the nightjars of the Old World. Except during migration, common nighthawks are mainly crepuscular (active around dawn and dusk), feeding on moths and other night-flying insects. They have extremely broad beaks and the inside of the mouth contains a sticky substance that presumably helps prevent prey from escaping.
During the day, nighthawks lie motionless on a horizontal limb or on the ground where their highly cryptic plumage renders them almost invisible. It is a fortunate event to find one at rest. Indeed, they rely so much on their camouflage that I once crept up to one roosting on the ground in a burned-over area, reached out and picked it up! It continued to remain motionless for a second or two before deciding to attempt escape.
Nighthawks nest on the ground or on flat, gravel-topped roofs. They used to be common in urban areas (one nested on the gravel roof outside my office window in the old Bell Museum on the University of Minnesota campus), but they have declined as gravel roofs have been replaced with smoother materials.
They have also declined significantly in recent years throughout their range (most of North America in summer and South America in winter). Though there is no smoking gun, it is widely believed that this may be due to the increased use of pesticides, resulting in much lower prey populations.
A final note: My wife, Janet, and I have two favorite nighthawk memories. While fishing near dusk on Lake Ida years ago, we were suddenly surrounded by a large flock of nighthawks dashing erratically like bats just over the water surface snatching emerging aquatic insects. The spectacle went on for several minutes and we were totally mesmerized.
The other incident involved a different nighthawk species, the sand-colored nighthawk, in Ecuador. Janet watched in early morning as hundreds of these birds flew up a small river after a night of feeding and landed on branches in one tree, where they proceeded to roost for the day.
For a new migratory experience, look skyward between 6 p.m. and dusk for common nighthawks between now and mid-September, especially on westerly or northwesterly winds.