California Spotted Owls - George Garnett, USFS

California Spotted Owl-NIGHT- NEWCalifornia spotted owls are one of the most fascinating raptors of the forest. I learned more about the California spotted owl from talking to Tahoe National Forest Wildlife Technician Emma Cox from the Yuba River Ranger District. Emma enjoys doing fieldwork and surveys as a wildlife technician for the U.S. Forest Service.

By visiting with Emma, I learned some basic facts about owls, the different sub-species of spotted owls, what they eat, and what eats them. Spotted owls are one of many birds of prey in California. This owl belongs to the order Strigiformes and the family Strigidae, the true owls. The Latin name of this fascinating owl is Strix occidentalis.

Perhaps the earliest known link between owls and wisdom is their association with Athena. The Greek goddess of wisdom is often depicted holding an owl.

First, some facts about owls. Owls are mostly nocturnal, which means they are active from dusk to dawn. Being a specialized predator, owls are equipped with many sophisticated features for prey detection and capture. For example, the wing feathers have fine fringes and velvety pile over the surface of the feather to deaden noise as it beats the air resulting in the ability to fly silently and surprise prey. Owls also have broad wings that help them maneuver through the trees. Their acute hearing helps them locate small prey from great distances even in total darkness. An interesting fact about the spotted owl is that “the flattened facial disk of the spotted owl funnels sound to the bird's ears and magnifies it to help the owl hear sounds humans are unable to detect,” explains wildlife technician, Emma Cox.

There are nine different species of owls inhabiting the Tahoe National Forest, but only the California spotted owl has the status of being a Sensitive species in the National Forest. Spotted owls, who nest in forested areas, often having large diameter trees of mixed tree species, were listed under the ESA due to historical alteration of its habitat as a result of timber management. The primary threats to its population in the United States have transitioned from timber harvest to an increased risk of stand-replacing wildland fire. These owls are also affected by the noise and disturbance associated with some human activities.

California Spotted Owl - NEW2There are three sub-species of spotted owl: The Northern spotted owls, found mainly in Washington, Oregon, Idaho and Northern California; California spotted owls, located in Nevada, Central and Southern California: and the Mexican spotted owls native to Mexico, New Mexico, Arizona, Colorado, Utah, and a small area of Texas. “Spotted owls located in these different areas tend to have their plumage (feathers) coloration blend with the environment where they live.” Explains Cox.

There is a lot of competition for suitable habitat. If they can make it through the first year, there is a good chance for survival. California spotted owls are considered mature and can breed after 2-3 years.

Spotted owls nest inside broken trees tops with live foliage above the opening for shade and protection. “Owls are opportunistic. They will use whatever is available for a nest because they do not build their own nests,” Cox said. “They’ve also been known to use witches brooms; which is a deformity where a dense mass of shoots grow from a single point resembling a broom or a bird's nest, for a nest.”

Owls prey on live (small) animals, and in non-scientific terms may be described as cats with wings. A spotted owls’ favorite meal consists of mice and, they tend to eat a lot of them. A single male owl must catch enough mice to feed himself, his female partner and several owlets in the nest. Although small mammals dominate the diet, the spotted owl is known to prey on squirrels, rabbits, birds, bats, and smaller owls. Once caught, the small prey is swallowed whole; larger prey must be torn into smaller pieces before swallowing. After consuming their meal, owls regurgitate castings, which are furry pellets of bones and other materials they’re unable to digest. These pellets are usually found on the ground below their nests and are a favorite scavenger hunt find with children.

Owls are not the only raptors in the forest vying for prey. Northern goshawks eat a wide range of prey including birds, mammals, squirrels, reptiles and owls.

“Northern goshawks will feed on owlets,” Cox said. “We believe they are responsible for the decapitated owls found in the Tahoe National Forest Goshawk territory.

One advantage of being nocturnal is that spotted owls can go undetected by goshawks and other diurnal birds of prey that are active during the day.

Males also respond to other male owl calls to protect their territory. Males feed the females until the eggs are hatched. Afterwards, the female will then teach the owlets to hunt and feed until they are able to catch prey on their own.

“The mating season usually begins in March,” says Cox, “and the gestation period is usually a little more than a month.” Owls usually live for up to 16–17 years.

OWL MOUSING 152 x 114All owls are territorial, particularly around active nests. With the spotted owl species, females are slightly larger than males. This is called sexual dimorphism, a condition where the two sexes of the same species exhibit different characteristics. Dimorphism occurs in many animals. Differences may include size, color, markings, and may also include behavioral differences. Male owls have to look good to attract the female.

A female will brood the eggs from 30-35 days. Once the eggs hatch, the female will stay with the young and will generally leave the nest only to defecate or to release her castings (furry pellets of bones and other indigestible material). She will occasionally get off the nest to take prey items from the male. For 7 to 10 days after the eggs hatch, the male will continue to feed the female and their young. Afterwards, the female takes over and will hunt and bring prey back to the nest, tear up the prey, and stuff it down the nestling’s mouth. The fluffy white balls grow quickly. After 10 to 15 days, they start to hop about. Once the young leave the nest they are called fledglings. After two weeks, the fledglings appear as large as an adult owl due to their fluffy down feathers.

They will have a territory they’ll protect for a long time and will not leave unless there is a fire or loss of habitat. During April or the first part of May they’ll select a nest tree to lay their eggs.

By the middle of June, the adult female will begin to entice the young to leave the nest area, teaching them to hunt and fly. By September she stops feeding them. It is at this point the fledglings hunt alone. If the young owls are not good hunters they perish; usually during the first year, due to starvation and predation. The mortality rate can be as high as 50 percent or greater during the first year.

“In the first year sub-adults are most prone to attack by other raptors in the forest,” Cox said, “sub-adults usually live along the periphery of suitable habitat and are called satellite-birds because they have not found a territory.”

Not only do owls hoot, owls also make a wide range of other sounds, such as screeches, whistles, barks, growls, rattles and hisses. During the nesting season, owl calls can often be heard from up to a mile away. Female owls generally have a higher pitched call than their mates.

Emma explained that while doing owl studies, she carries a terrarium full of white mice. She then “hoots” to attract owls during the night. If she doesn’t see any owls during the night, she tries again in the early morning. Once she spots an owl, she removes a mouse from the terrarium box and uses it for bait to attract the owl. Once the owl takes the mouse, she then follows the owl to see if they return to their nest to feed the nestlings. If, Emma and her crew are fortunate, they’ll get to see the young “fluff-balls” of doom!

(Photo credits: Macauley Mathieu-Busher)