The general plumage of the Tawny Frogmouth is silver-grey, slightly paler below, streaked and mottled with black and rufous. A second plumage phase also occurs, with birds being russet-red. The eye is yellow in both forms, and the wide, heavy bill is olive-grey to blackish. The body length ranges from 35 - 50 cm, with south-eastern birds being larger than birds from the north. Tawny Frogmouths are often confused with owls, but are actually more closely related to the nightjars.
Tawny Frogmouths breed mainly from August to December, although birds in more arid areas may breed in response to heavy rains. The parents tend to use the same nests, usually placed on a horizontal forked tree branch, making annual repairs to their flimsy structures of sticks and twigs, if needed. After mating, the female lays 2-3 eggs into her nest, usually laying each egg 1 - 3 nights apart. Both sexes incubate the eggs for 30 days. The male sits during the day, but both sexes share sitting at night. Normally only one brood is raised in a season, but birds from the south may have two. The fledging period is about 30 days. Feeding is shared by parents.
It can be seen in almost any habitat type except the denser rainforests and treeless deserts. A nocturnal bird, the frogmouth occupies a roosting perch in daylight, remaining motionless unless directly disturbed. Under extreme circumstances, it sometimes will employ an aggressive display by opening its huge mouth while clapping and extending its wings. The feet are weak and lack the curved talons of owls. Vocalization is a repeated booming or grunting “oom”. Frogmouths are monogamous, finding a mate and staying with this same partner year after year, until one bird eventually dies.
The bulk of the Tawny Frogmouth's diet is made up of nocturnal insects, worms, slugs and snails, small mammals, reptiles, frogs and birds. Rapid fliers, they quickly swoop down on prey, using the powerful bill on victims before swallowing. Some prey items, such as moths, are caught in flight, which has led to many unfortunate instances of birds being hit by cars while chasing insects illuminated in the beam of the headlights.