Owls are easy to recognize. They have an almost human appearance, with upright posture, large rounded heads, and large eyes that face forward (most birds have eyes on the sides of their heads). All owls are carnivores, or meat-eaters, and several adaptations make them effective hunters, including a hooked beak for tearing flesh and strong feet tipped with sharp talons, or claws. The toes can be used in a two-forward, two-backward arrangement for a good grip on prey (most birds have three toes pointing forward and one pointing backward). Feathers are unusually soft, allowing for silent flight, so owls can hear their prey and approach it without warning.
Most owls are nocturnal, active at night and asleep by day. Adaptations for night hunting include eyes that can see in low-light conditions and very sensitive hearing. The eyes are enclosed in a ring of bone and cannot move freely, so owls must turn the entire head to look sideways. They do have extra flexible necks that allow the head to turn 270°, so an owl can see what's behind its back. Many owls have ears positioned asymmetrically on the head, with one higher than the other. This arrangement helps owls locate the source of a sound. Feathers on the face are arranged in a flat circle called a facial disk. It works much like a satellite dish, focusing sound waves on the ear openings.
Most owls have subdued, or dull, color. The feathers are usually gray or brown with spotted or streaky patterns that create a camouflage effect, allowing the owl to blend in with its surroundings. This is useful when owls are sleeping during the day. The owls avoid being noticed by predators such as hawks. Male and female owls usually look alike but females are often are slightly larger.
The heaviest owl is the Eurasian eagle-owl, which weighs
9.25 pounds (4.2 kilograms). At 28 inches (71 centimeters), however, it is a little shorter in length than the great gray owl, which measures 33 inches (84 centimeters) long. The smallest owl is the elf owl, which weighs 1.4 ounces (40 grams) and is about 5 inches (13 centimeters) long.
Owls are found on every continent except Antarctica. The tropics support the greatest variety of owl species.
The vast majority of owl species are forest dwellers. Few species live at high elevations or in very dry habitats. Most owls are sensitive to disturbance, but a few species adapt well to living among humans in suburban or urban areas. The eastern screech-owl is a good example. Members of the group called fishing owls are unusual for their habit of living near forest streams or in mangrove swamps and feeding mostly on fish. Only a few owl species undergo true migrations. Most species live in the same place year round. In winters when populations of small rodents such as lemmings or voles are low, northern owls may leave their usual home ranges and invade southern regions.
All owls are carnivores. They catch small animals with their feet, kill them with a bite to the neck, and swallow them head-first. Most owls hunt from a raised perch. They sit, watch, and listen, then swoop or glide to their prey. At the last minute, they swing their legs forward and spread their talons to strike. Very large owls (such as eagle-owls) take medium-sized mammals such as rabbits, skunks, and monkeys. Medium-sized owls take mostly small mammals, such as voles, rats, mice, and shrews. Small owls feed mostly on insects along with other invertebrates such as snails, spiders, scorpions, moths, or crickets. Many owls occasionally take bats, birds, small reptiles, and amphibians in addition to their preferred prey. Many species cache (KASH), or store, extra prey to eat later. In cold climates cached prey may freeze. The owl just sits on it to thaw it. Owls swallow their prey whole but cannot digest hard bones, fur, and feathers. These materials are later coughed up in a neat package called an owl pellet.
BEHAVIOR AND REPRODUCTION
Most owls are active at night and sleep by day. Usually owls roost in sheltered spots—thick foliage or a branch close to a tree trunk. Some people think owls are "tame" because roosting owls may allow humans to come quite close. Actually, this behavior is an adaptation for avoiding detection by predators. If they're disturbed, owls pull their feathers in tight to look slim and lean close to the tree trunk to avoid being noticed. A few species are active by day, notably the snowy owl. This species lives in the Arctic, where daylight lasts twenty-four hours in the breeding season.
Because owls are active at night, they depend more on their ears than their eyes to communicate with other owls. Males mostly use vocalizations (sounds), rather than colorful feathers or flight displays, to get a female's attention. Owls also call to defend their territory and to stay in touch with each other. In most species, both sexes vocalize but the male calls more than the female.
Most owls are solitary. They hunt and roost alone, except during the breeding season. Most owls breed just once a year. They do not build their own nests. The smallest owls often nest in abandoned woodpecker holes. Larger owls use old crow or raptor nests, the top of a snag (a dead tree, standing, with the top broken off), a tree hole, a natural cave, or an abandoned building. A few species nest on the ground, including snowy owls and short-eared owls. Burrowing owls nest underground in prairie dog, badger, or ground squirrel burrows. Female owls do not gather any nest material. Eggs are laid on bare ground or the floor of the tree cavity.
A male and female owl bond by preening each other, straightening and cleaning their feathers. In many species, the male offers a gift of food to his mate. Owl eggs are white and more round than oval. A typical clutch ranges in size from two to four eggs for small owls to five to eight eggs for larger owls. In most species, the female lays one egg a day until the clutch is complete. But where many songbirds start to incubate the eggs after the clutch is complete, female owls start incubating with the first egg. That means the owlets hatch on different days and are of different sizes. Often, the youngest, smallest nestlings do not survive.
OWLS AND PEOPLE
Owls have always inspired the human imagination. A Paleolithic rock painting of an owl is one of the oldest known human drawings. The Bible describes owls as birds of waste places and forbids eating them. In many cultures owls are considered bad omens or creatures of the underworld, probably because they fly at night and have spooky-sounding calls. The sight or sound of an owl is thought to warn of death. This idea is seen repeatedly in the plays of William Shakespeare.
Not every culture has feared owls. In ancient Greece the owl was the symbol of Athena, the goddess of wisdom. In their nighttime activity, owls were thought to be like hard-working scholars. Owls continue to be a symbol of education in the United States in the twenty-first century.
As of 2003, the IUCN lists seven owl species as Critically Endangered, facing an extremely high risk of extinction, or dying out, in the wild; nine species as Endangered, facing a very high risk of extinction in the wild; and eleven species as Vulnerable, facing a high risk of extinction in the wild. A number of owl species occur on only one small island or in one small area. That makes these species particularly vulnerable to extinction.
In the United States two owl species are protected under the Endangered Species Act. The ferruginous pygmy-owl is listed as Endangered and the spotted owl is listed as Threatened.
BIRDS OF PREY?
For a long time, owls were thought to be close relatives of birds in the order Falconiformes (the hawk-like birds). The two groups do have a lot in common. Both are hunters with excellent eyesight. They have strong legs and sharp talons for catching prey. They have hooked beaks for killing and eating their prey. The term "birds of prey" is still often used to describe the two groups. In 1985, however, researchers took a careful look at bird DNA. They decided owls are most closely related to birds in the order Caprimulgiformes, or nightjars. Besides the genetic evidence, there are other similarities between these two groups. Both are active at night, their voiceboxes are similar, and their feathers are arranged in the same way.
Habitat loss because of logging or agriculture is the biggest problem for owls. Other causes of mortality include illegal shooting, collisions with cars and human-built structures, electrocution on power lines, and poisons used against rats and mice.
FOR MORE INFORMATION
BirdLife International. Threatened Birds of the World. Barcelona and Cambridge, U.K.: Lynx Edicions, 2000.
Duncan, James R. Owls of the World: Their Lives, Behavior and Survival. Buffalo, NY: Firefly Books, 2003.
Johnsgard, Paul A. North American Owls: Biology and Natural History. Washington, DC: Smithsonian Institution Press, 2002.
Lewis, Deane P. The Owl Pages. http://www.owlpages.com (accessed on June 25, 2004).