A number of North American birds are more active at night than during the day -- that is, they’re nocturnal. Nocturnality allows birds to avoid certain diurnal, or day-active, predators; exploit prey out and about under the cover of darkness; or otherwise take advantage of particular nighttime conditions. Birds specialized for the after-hours lifestyle sometimes have proportionally large eyes -- to better take advantage of dim light -- or exhibit other special adaptations. Several groups of nocturnal North American birds particularly stand out.
The best-known nocturnal birds in North America are the owls, nighttime counterparts of falcons, hawks and eagles. North American owls range in size from the little elf owl of the southwestern deserts to the massive and formidable snowy and great horned owls. Besides stellar night vision and hearing, owls rely on nearly silent flight to approach prey: The leading edge of their wing-feathers is jagged, or “fluted,” muffling air turbulence for quieter wingbeats. Not all North American owls fall in the nocturnal category: The northern and ferruginous pygmy owls, northern hawk owl, short-eared owl, and snowy owl are mostly diurnal.
Nightjars and Nighthawks
These rather strange-looking birds, which belong to the family Caprimulgidae, sometimes go by the collective name “goatsuckers,” thanks to an archaic -- and erroneous -- belief that they robbed goats of their milk. Camouflaged like leaf litter or bark, nightjars and nighthawks spend the day resting on the ground or heavy branches, then take wing at night to snatch insects out of the air with their huge, bristle-lined mouths. Nightjars are famous for their loud, loopy calls, which give several North American species -- the whip-poor-will, Chuck-will’s-widow and poor-will -- their onomatopoeic names. Somewhat more conspicuous than the big-headed nightjars are the nighthawks, slimmer and longer-winged birds that are often seen hunting the dusk skies.
The Night Herons
The black- and yellow-crowned night herons are two closely related wading birds most active, as their names suggests, after the sun's gone down. During the day, the birds roost, often communally, in trees or shrubs. Both are relatively small and stocky herons, though the yellow-crowned is more slender than the other. Black-crowned night herons have an enormous global range and are widely distributed in the United States; yellow-crowned night herons are restricted to the Southeast. The two relatives also diverge a bit diet-wise: Though both stalk wetlands, lakes and rivers, the black-crowned mostly targets fish, while the yellow-crowned is mainly a crab and crayfish eater.
A number of seabirds are primarily or occasionally nocturnal, a trait that -- in addition to helping them avoid predation by raptorial birds -- allows them to take advantage of night-active fish, squid and plankton, and also helps them navigate by celestial clues. Nocturnal seabirds in North America include many petrels, shearwaters and auks, such as the rhinoceros auklet of the Pacific coast. Such night fliers can be attracted or disoriented by the lights of fishing boats, oil platforms and other man-made apparatuses.
Many kinds of otherwise diurnal North American birds migrate at night, including numerous species of songbirds and shorebirds. For long-distance migrants, nocturnal travel offers a number of advantages: The typically calmer and cooler atmospheric conditions make it easier and less exhausting to fly, and there’s less threat of predation given daylight-hunting hawks and falcons aren’t an issue. You can often detect night-flying migrants by listening for their vocalizations or watching a bright moon through binoculars or a spotting scope: On heavy migration nights, you might spot the silhouettes of steadily passing birds.