The northern spotted owl (Strix occidentalis caurina ) is one of three spotted owl subspecies. A western North American bird in the family Strigidae, genus Strix, it is a medium-sized dark brown owl native to the Pacific Northwest. An important indicator species, the northern spotted owl remains threatened due to continued population decline from human-caused habitat destruction and competition with invasive species, its main competitor being the barred owl.
Northern spotted owls have dark brown plumage with white spots and no ear tufts. They are typically around sixteen to nineteen inches in length and one to one and one sixth pounds. Females are about 10-20% larger than males. Their wingspan is approximately 42 inches. They are a mainly nocturnal species, and form long-term pair bonds. While most owls have yellow to red-orange colored eyes, northern spotted owls are one of the few owls with darkish to black-colored eyes.
The northern spotted owl primarily inhabits old growth forests in the northern part of its range (Canada to southern Oregon) and landscapes with a mix of old and younger forest types in the southern part of its range (Klamath region and California). The subspecies' range is the Pacific coast from extreme southern British Columbia to Marin County in northern California.
Most spotted owls inhabit federal lands (Forest Service, Bureau of Land Management, and National Park Service lands), although significant numbers occur on state lands in Washington, Oregon, and California, as well as tribal and private properties.
Northern Spotted Owls range on 500,000 acres of the 7.6 percent of private forestlands managed by Native American tribes in the state of Washington. Federally recognized tribes are treated as sovereign governments, and each recognized tribe is responsible for their own management plans for the northern spotted owls in their area. Regardless of tribal or private ownership, however, the United States federal government requires all land owners and inhabitants to comply with the Endangered Species Act.
The northern spotted owl nests in cavities or on platforms in large trees. It will also use abandoned nests of other species. Northern spotted owls remain in the same geographical areas unless forced out from harsh conditions or lack of food.
The northern spotted owl is intolerant of habitat disturbance. Each nesting pair needs a large amount of land for hunting and nesting, and will not migrate unless they experience drastic seasonal changes, such as heavy snows, which make hunting difficult. Their flight pattern is distinct, involving a series of rapid wingbeats interspersed with gliding flight. This technique allows them to glide silently down upon their prey.
The northern spotted owl diet consists of small mammals (91.5%), other birds (4.3%), insects (4.1%), and other prey (0.1%). These prey are most nocturnal (91.9%) or active during the day and night (4.8%), which corresponds to the primarily nocturnal nature of the northern spotted owl. The main species consumed by the northern spotted owl are northern flying squirrels (Glaucomys sabrinus ), woodrats (Neotoma fuscipes and N. cinerea ), red tree voles (Arborimus longicaudus ), western red-backed voles (Clethnonomys californicus ), deer mice (Peromyscus maniculatus ), and gophers (Thomomys spp.). Consumption of these small mammals varies by habitat region and proliferation of small nocturnal mammals. Recent invasion of barred owls (Strix varia ) into the northern spotted owl range has resulted in decreased food availability due to overlap in dietary preferences.
Northern spotted owls reach sexual maturity at two years of age, but do not typically breed until three years of age. Males and females mate in February or March, with the female laying two or three eggs in March or April. Eggs are incubated by the female for around thirty days until hatching. After hatching, the young owls remain in the nest and the adult female provides primary care. Fledgling occurs in 34 to 36 days. The hunting and feeding is done by the male during this time. The young owls remain with the parents until late summer to early fall. They leave the nest and form their own winter feeding range. By spring, the young owls' territory will be from 2 to 24 miles from the parents.
The barred owl is an owl species native to the Eastern United States, but has invasively expanded west into the habitat ranges of the northern spotted owl. Invasion of barred owls into the northern spotted owl’s habitat has occurred recently, with all of northern spotted owl territory now also inhabited by the barred owl. Barred owls have a diet of small mammals (74.7%), other birds (8.3%), amphibians (6.4%), bugs (5.6%), crayfish (3.0%), fish (1.5%), reptiles, snails and slugs, and earthworms (<1.0% each). This diet is similar to the northern spotted owl, and the introduction of barred owls to the northern spotted owl’s range creates increased competition for food. In the same areas, northern spotted owls require around three to four times more range than barred owls, which places more strain on the northern spotted owls. As barred owl population densities increase, the strain of food competition will worsen for northern spotted owls.
The greater diversity of diet in the barred owl, notably in the amphibians, crayfish, and fish consumed, threatens ecological stability due to extended predation now experienced by affected species. The additional food sources also give an advantage to the barred owl over the northern spotted owl, worsening the northern spotted owl's ability to compete. Paired with more predation of prey that is shared between the barred owl and the northern spotted owl, the introduction of the barred owl in these areas may have unknown long term effects on the ecological balance of these habitats. The most drastic effect is on the northern spotted owl population, which is estimated to have decreased at an annual rate of 3.8% from 1985 to 2013. This population loss is directly related to the presence of barred owls. The Diller et al. (2016) study demonstrated that lethal removal of barred owls resulted in the northern spotted owl populations to increase, while populations of northern spotted owls continued to decrease if barred owl populations were left alone. Should northern owl habitat areas continue to be protected under the Northwest Forest Plan and other related legislation, solutions to regulate barred owl populations could reverse the population decline of the northern spotted owl. Without intervention, continued annual decrease in population levels would ultimately end in extinction of the northern spotted owl.
There are fewer than 6 individuals left in British Columbia, Canada; 1,200 pairs in Oregon, 560 pairs in Northern California, and 500 pairs in Washington. Washington alone has lost over 90 percent of its old growth forest due to logging which has caused a 40-90 percent decline of the Northern Spotted Owl population.
The worldwide IUCN Red List of Threatened Species status for the spotted owl species is "Near Threatened" with a decreasing population trend. As the IUCN Red List does not track subspecies, this status is applied to species across its whole range in Canada, the United States and Mexico.
The Canadian population, declared endangered by the Committee on the Status of Endangered Wildlife in Canada under the 2002 Species at Risk Act, now numbers less than 100 breeding pairs of birds. In British Columbia, Canada, as of 2010, only 6 pairs are known in the wild, down from historic numbers of 500 pairs.
The northern spotted owl was listed as a threatened species under the Endangered Species Act throughout its range of northern California, Oregon and Washington by the United States Fish and Wildlife Service on June 23, 1990 citing loss of old-growth habitat as the primary threat. The USFWS previously reviewed the status of the northern spotted owl in 1982, 1987 and 1989 but found it did not warrant listing as either threatened or endangered. Logging in national forests containing the northern spotted owl was stopped by court order in 1991.
In 2007 a Captive Breeding and Release Program was created in Langley, British Columbia, Canada, with the goal of producing owls in captivity for release into protected habitat to prevent the extirpation of the species from Canada. The short-term goals of the Program include growing the captive population to 10 breeding pairs and releasing 10-20 offspring per year into the 300,000 hectares of protected old-growth forest. Long-term the Breeding Program aims to recover the wild population to self-sustaining numbers, approximately 300 adults, over the next 10–20 years.
In 2021, there were only 3 individuals left in the wild in Canada.
