(adjective) Describes birds that are principally active at night with hunting, feeding and other behaviors, and that roost and sleep during the day. These birds typically have superior vision to allow for low level sight, or their other senses are heightened to compensate for less useful vision.
While owls, nightjars, frogmouths and similar species are principally nocturnal, other birds do exhibit some nocturnal behavior. Many songbird species will migrate at night in the spring and fall, and both the northern mockingbird and the American robin have been recorded singing extensively at night. Despite these limited behaviors, however, birds are typically only considered nocturnal if the majority of their daily life activities occur at night.