The spotted owl is a football-sized, chocolate brown owl with black eyes and a white-spotted breast. It weighs about a pound, has a wingspan of about three feet and has no ear tufts. There are three sub-species of spotted owl. The Northern, Strix occidentalis caurina, (the focus of our study) is found from British Columbia (but only four pair remain in that province) to Northern California. The California spotted owl is found in the Sierra Nevadas and the Mexican spotted owl lives in the desert southwest. Only the Northern and the Mexican have been federally listed under the Endangered Species Act, although there was a failed motion to list the California spotted owl in 2006.
Spotted owls are long-lived, with certain individuals reaching almost thirty years of age. They tend to mate for life and stay in the same patch of habitat year after year. In the winter, when food is hard to come by, members of a pair split up, hunting in different sections of their single large territory. In late February or early March they reconvene. Northern spotted owls nest on average only every other year, but in years when they don’t nest they often summer together anyway, roosting in proximity and preening each other regularly. This endearing behavior may have evolved to combat the high diversity and abundance of parasites that they host.
Spotted owls don’t really build nests. Instead they lay their eggs on branches, in nests made by other birds like goshawks, or in cavities. We would never find their “nests”, which are often high up in mature Douglas Firs, if we didn’t offer the owls mice, which a male will take to the female during incubation or an adult of either sex will take to the nestlings. Females incubate their eggs continuously while males provide all of the food for themselves, their mates and their chicks until ten days or so after hatch. After that time females start to interrupt incubation to help feed the young. Most of the time spotted owls lay two eggs, less commonly one or three. If the eggs of young are eaten or fall to their death then the pair will not renest for the year.
Spotted owls in Washington eat primarily flying squirrels. Here in California they eat mostly woodrats, but also flying squirrels, ground squirrels, voles, mice, lizards, and the occasional Jerusalem cricket when other food is scarce. Owls eat their prey whole or in huge bites. Bones, hair, feathers and other parts difficult to digest are strained by the gizzard and compacted into a pellet which is regurgitated 10-12 hours after the meal.
Spotted owls hunt at night, and, like other nocturnal predators, have keen sight and hearing. Their eyes are shaped not as balls like ours but as deep tubes into their heads, designed to gather and process as much light as possible. Because of their tube design, owl eyes cannot rotate. To compensate the neck has many vertebrate and is very flexible, allowing for an enormous range of motion.
Owl ears are set at differing heights on the head to help locate the source of sound. Using differences in the time sound waves hit the two ears (left-right and up-down), spotted owls can pinpoint the location of rodents or other prey very accurately. Their disk-shaped faces are used to help channel sound waves to the ears.
Owl feathers are specialized to make them almost completely silent in flight. If you get a chance to inspect a wing feather you will find that it is brown and white striped, very soft and doesn’t make a sound as you swish it through the air. Look closely and you will see that the front edge is fringed like a comb. This breaks up the air into micro turbulence to minimize sound and provide stability. The trailing edge of the feather ends in a loose fringe. This helps breaks up the turbulence even further. The military is now experimenting with planes that mimic aspects of owl feather design to increase their stealth. See great close-ups of owl feathers and read more about it here:
owlpages.com
Because spotted owls spend almost all their time under the forest canopy and hunt by perching, listening and pouncing, their wings and feathers are not adapted for long flights or soaring. The wings are large for body size, however, enabling owls to fly slowly while hunting. During the day spotted owls roost on branches of trees like Douglas Firs, often next to the trunk where their camouflage makes them almost invisible. They have few predators, but young owls can be killed by other owls like the great-horned owl or by goshawks.
Spotted owls rely on old growth forest for roosting habitat, which is essential to their survival. Because woodrats flourish in younger stands, spotted owls often have an easier time feeding their young when their territories include some earlier successional forest. They don’t survive well without old growth stands for protection, though.
Lately the barred owl has been invading the historic range of the spotted owl. Barred owls are closely related to spotted owl, members of the same genus in fact. They look very similar except that they are greyer and have a striped (or “barred”) breast. In the field they are easy to tell apart because barred owls make a “who cooks for you?” call and are much more aggressive. Barred owls are native to the east coast of North America but began to spread west through clear-cut forests in Canada in the 1940s. Now they are moving south through the Pacific Northwest, displacing spotted owls as they go. While some biologists are experimentally removing barred owls from former spotted owl territories (shooting them), no one yet has a good plan for managing barreds to protect the federally threatened Northern spotted. The Northern spotted owl is declining at a rate of about 4 % annually, although rates of decline differ across its range from 7.7% annually in Washington to 2.2% annually in California from 1990 to 2003.