This medium-sized bird has large, flattened head and long, narrow, pointed wings. The bill of Common nighthawks is small while the mouth and eyes are large. The long tail is notched and brown with buff bands. Across the long feathers, bordering the wings, the bird has wide white stripe, which is visible when flying. The throat band of female nighthawks is buff-colored whereas that of males is white. In addition, male nighthawks have a white stripe near the tip of the tail. Juveniles can be identified by the absence of buff-colored or white throat band.
The area of their distribution covers nearly all of North America, including all provinces and territories of Canada, except with Nunavut. They also nest in some parts of Central America and, possibly, in southeastern Columbia. The Common nighthawk occurs mainly in open, vegetation-free terrains such as recently harvested forests, burnt-over and logged areas, lakeshores, river banks and beaches, dunes, rocky outcrops and rocky barrens, peat bogs and swamps, grasslands and pastures. These birds can also be found in mixed and coniferous forests.
Common nighthawks are very territorial animals with males, fiercely defending their territory by diving at intruders. These birds are solitary nesters. They are crepuscular animals, feeding at dusk, dawn and at night. The rest of the time they spend sleeping or roosting. In addition, they tend to sunbathe on tree branches, the ground, flat rooftops or fence posts. These birds gather in large migrating flocks, sometimes containing hundreds or thousands of individuals. They travel huge distances, leaving for South America in September and wintering there. They return to their northernmost breeding grounds in Yukon Territory (North-western Canada) only in the beginning of June.
Common nighthawks are monogamous. Breeding season lasts from mid-March to the beginning of October. The female usually lays 2 eggs with the interval of 1-2 days, incubating the eggs for 18-20 days. The chicks are semiprecocial, starting to respond to their mother's call within the first day of their lives. In evenings, the female leaves the nesting site to forage. The hatchlings feed upon regurgitated insects. At the age of 16 days they are able to hop while the first flight is at 18 days old. At 25-25 days old, the young can fly well, and by the age of 30 days they leave the nest. The young are fully developed at 45-50 days old, joining flocks of migrating nighthawks.
The major threats to this species' population are alteration and loss of habitat. Another concern is population decline of insect species due to widespread use of insecticides, climatic fluctuations at breeding sites and during migration and collisions with motor vehicles. Other threats include: fire suppression; intensive agriculture with reforestation of abandoned agricultural fields and harvested forests; reduction of flat rooftops, covered with gravel.
The overall population number of this widespread species is unknown but presently decreasing. The estimated population in Canada is about 400.000 breeding adult individuals. On the IUCN Red List, the species is classified as Least Concern (LC).
These birds control populations of prey species they feed upon. In addition, they compete for food with lesser nighthawks and bats.