The Owl Is a Different Kind of Bird in Many Ways
Owls utilize virtually all habitats, from grassland and tundra to dense woodland and rainforest. The distribution and density of most species seem to be limited by the availability of suitable nesting sites, rather than by the number of potential prey animals. In general, the type of prey taken is dictated by the size of the owl and by the relative abundance of potential prey. Owls that hunt over grassland, such as the barn owl and short-eared owl, hunt by sustained flight, dropping into the grass to catch rodents. Many woodland owls secure prey by dropping from perches at the edges of forest openings. A variety of owls may depend on a single prey species when it becomes exceptionally abundant. Prey is generally swallowed whole, and indigestible material, such as feathers fur, and bones, are regurgitated in the form of a compact pellet.
Sound is important to owls, especially in mating and territorial defense. Camouflage, daytime immobility, and silent flight may combine to make it as difficult for owls to see each other as it is for natural enemies and human observers to see them. Usual owl sounds include snaps of the bill, claps of the wings in flight, and a variety of vocalizations, with pitches, timbres, and rhythms unique to each species. Although less melodious than the calls of some birds, the vocalizations of many owls are “songs” in the biological sense and can even be musical to the human ear. The song varies from deep hoots in some large species to chirps, whistles, or warbling in many small owls. The nocturnal routine of most owls involves peaks of activity at dusk and dawn. The owl leaves its secluded roost about dusk and moves to a perch overlooking the hunting area. There is a brief period of song, followed by about half an hour of foraging, then a longer period of song. Most of the darker hours of the night are spent inactively, with a period of alternating singing and hunting just before dawn.
Most owls add no nesting material to the site, but the fur and feathers of accumulated prey remains and regurgitated pellets may provide some cushion for the eggs. When an open nest is used, leaves, grass, or other soft material may be added as a lining. Intense competition has been observed among nesting birds, including owls, for occupancy of a limited number of nest sites. Egg laying is timed such that the young become independent of their parents at a time when prey populations are greatest. At northern latitudes, many owls nest in the spring a month or two earlier than hawks, with the result that an incubating owl is frequently covered by several inches of snow. Barn owls have been found nesting in every month of the year, even at the northern edge of their range, but the peak of nesting is in the spring. While in the nest, young owls grow two successive coats of white natal down. In the smaller species, the down is replaced by the immature juvenal plumage of softer, lacier texture than that of the adult. At this age, about two-thirds of the way to fledging, the young owls may leave the nest and spend the day several meters from it. Most owls use their feet only for perching and grasping prey. The burrowing owls, however, being terrestrial, can run rapidly over the ground and rarely perch in vegetation. The typical owl perch is a horizontal branch in a tree. The flight of owls is a steady flapping on a straight path, ending in a short upward glide to the perch. Hunting, usually done from a perch, rarely involves extensive flight, requiring only a short burst of speed to surprise the prey on the ground.
