Northern spotted owl

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.

Strix occidentalis caurina
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Strix
Species:
S. occidentalis
Subspecies:
S. o. caurina
Trinomial name
Strix occidentalis caurina
(Merriam, 1898)

Description

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 dark-colored eyes.

Vocalizations

Thirteen different sounds of hoots, whistles, and barks have been identified to be sounds of the northern spotted owl, with females having higher pitched calls than males. Of the three different styles of calls, hoots appear to be most commonly used to announce things, such as territory and prey. The whistles are often used by the females to present themselves to the males, and the barks during territorial issues between owls. [1]

Distribution and habitat

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.[2]

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.

Diet

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.[3] 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.[3] 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.[4]

Behavior

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.[5]

Reproduction

Northern spotted owls reach sexually mature at two years of age, but do not typically breed until three years of age. Male 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.[6]

Conservation
Northern spotted owl, Oregon Zoo, Portland, Oregon

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[when?] 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.[7] 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.

Controversy

In 1990, the logging industry estimated up to 30,000 of 168,000 jobs would be lost because of the owl's status, which agreed closely with a Forest Service estimate.[8] Harvests of timber in the Pacific Northwest were reduced by 80%, decreasing the supply of lumber and increasing prices.[6] However, jobs were already declining because of dwindling old-growth forest harvests and automation of the lumber industry.[8] One study at the University of Wisconsin–Madison by environmental scientists argued that logging jobs had been in a long decline and that environmental protection was not a significant factor in job loss.[9] From 1947 to 1964, the number of logging jobs declined 90%. Starting with the Wilderness Act of 1964, environmental protection saved 51,000 jobs in the Pacific Northwest.[10]

The controversy pitted individual loggers and small sawmill owners against environmentalists. Bumper stickers reading Kill a Spotted Owl—Save a Logger and I Like Spotted Owls—Fried appeared to support the loggers.[8] Plastic spotted owls were hung in effigy in Oregon sawmills.[11] The logging industry, in response to continued bad publicity, started the Sustainable Forestry Initiative.[12] While timber interests and conservatives have cited the northern spotted owl as an example of excessive or misguided environmental protection, many environmentalists view the owl as an "indicator species," or "canary in a coal mine" whose preservation has created protection for an entire threatened ecosystem.[13]

Protection of the owl, under both the Endangered Species Act and the National Forest Management Act, has led to significant changes in forest practices in the northwest. President Clinton's controversial Northwest Forest Plan of 1994 was designed primarily to protect owls and other species dependent on old-growth forests while ensuring a certain amount of timber harvest. Although the result was much less logging, industry automation and the new law meant the loss of thousands of jobs.[14] However, new jobs were created for biologists conducting surveys for spotted owls and other rare organisms that occur in their range.

The debate has cooled somewhat over the years, with little response from environmentalists as the owl's population continues to decline by 7.3 percent per year.[15] In 2004 the U.S. Fish and Wildlife Service reaffirmed that the owl remained threatened, but indicated that invasion by barred owls into the range and habitat of the spotted owl was also a cause of declining spotted owl populations.

In 2007, the USFWS proposed a new recovery plan intended to guide all management actions on lands where spotted owls occur, and to aid in recovery of the species. Early proposals were criticized by environmental groups as significantly weakening existing protections for the species. The Obama administration reversed proposals that would have increased logging on Bureau of Land Management administered lands. Recent discussion has been focused on two novel approaches. One of these would emphasize wildfire management as key to owl persistence on the east side of the Cascades, and in the Klamath province. Another proposal, on control of barred owl populations through culling,[16] has been criticized by some animal rights and other activists.[17]

Federal biologists were considering in 2010 whether to kill barred owls to see if that would help the spotted owls.[18][19][20]

In early 2021, The Trump administration removed more than 3 million acres of Pacific Northwest land from the protected habitat of the northern spotted owl, 15 times the amount it had previously proposed opening to the timber industry. Aurelia Skipwith, director of the Fish and Wildlife Service, stated that "these common-sense revisions ensure we are continuing to recover the northern spotted owl while being a good neighbor to rural communities within the critical habitat" even though northern spotted owl populations continue to decline.[21]

Influence of barred owl invasion

Population decline of northern spotted owl

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.[22] 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).[4] 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.[3] 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.[4] 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.[23] 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.[24] 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.[24] 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.

Hybridization

Northern spotted owls and barred owls have been shown to be capable of producing hybrid offspring. Previous geographical isolation had prevented prior hybridization, and current ones are difficult to distinguish from nonhybrids without using genetic testing techniques. However, of those differences that are discernable, hybrids tend to be larger and lighter colored than northern spotted owls, with similar facial features to barred owls.[25] All hybridization occurred between male northern spotted owls and female barred owls. Cross-breeding amongst the species is a very limited event, and likely insufficient to be significantly detrimental to either species. Direct competition between species for habitat space and food is determined to be much more significant issues in affecting both target populations.[26] There has also been genetic evidence of cross breeding between northern spotted owls and California spotted owls (S. o. occidentalis), but since both are subspecies of the same species, this is not truly considered hybridization.[27]

See also

References
  1. Courtney, Stephen P.; Blakesley, Jennifer A.; Bigley, Richard E.; Cody, Martin L.; Dumbacher, Jack P.; Fleischer, Robert C.; Franklin, Alan B.; Franklin, Jerry F.; Gutiérrez, Rocky J.; Marzluff, John M. & Sztukowski, Lisa (September 2004). Scientific Evaluation of the Status of the Northern Spotted Owl (PDF) (Report). Portland, Oregon: Sustainable Ecosystems Institute.
  2. "WFPA - NSO Conservation in WA - Tribal Forestland". www.northernspottedowl.org. Retrieved February 24, 2016.
  3. Forsman, Eric D.; Bruce, Charles R.; Walter, Mary A.; Meslow, E. Charles (1987). "A Current Assessment of the Spotted Owl Population in Oregon". The Murrelet. 68 (2): 51. doi:10.2307/3535693. ISSN 0027-3716. JSTOR 3535693.
  4. Livezey, Kent B. (September 2007). "Barred Owl Habitat and Prey: A Review and Synthesis of the Literature". Journal of Raptor Research. 41 (3): 177–201. doi:10.3356/0892-1016(2007)41[177:bohapa]2.0.co;2. ISSN 0892-1016.
  5. "Northern Spotted Owl". Defenders of Wildlife. Retrieved October 30, 2008.
  6. Brokaw, Jeanne (Nov/Dec 1996). "Does Anybody Give a Hoot?" Mother Jones. Accessed April 3, 2013.
  7. Northern Spotted Owl Breeding Program
  8. Satchell, M. (June 25, 1990) U.S. News & World Report, Vol. 108, Issue 25, p. 27.
  9. Freudenburg, William R.; Lisa J. Wilson; Daniel O'Leary (1998). "Forty Years of Spotted Owls? A Longitudinal Analysis of Logging-Industry Job Losses" (PDF). Sociological Perspectives. 41 (#1): 1–26. doi:10.2307/1389351. JSTOR 1389351. S2CID 37523161. Archived from the original (PDF) on August 30, 2006. Retrieved November 12, 2008.
  10. Guglielmino, Janine (Summer 1997). American Forests, Vol. 103, Issue 2, p. 6.
  11. Adams, Larry (December 1999). Wood & Wood Products, Vol. 104, Issue 13, p. 62.
  12. Sustainable Forestry Initiative. aboutsfi.org
  13. "American Lands Alliance Action Alert". Americanlands.org. May 15, 2007. Archived from the original on June 13, 2007.
  14. Knickerbocker, Brad (June 27, 2007). "Northern spotted owl's decline revives old concerns". Christian Science Monitor. Retrieved June 27, 2007.
  15. "How Should We Manage the Barred Owl?" Olympic Peninsula Audubon Society. Accessed April 3, 2013.
  16. Johnson DH, White GC, Franklin AB, Diller LV, Blackburn I, Pierce DJ, Olson GS, Buchanan JB, Thrailkill J, Woodbridge B, Ostwald M. (2008). Study designs for Barred Owl removal experiments to evaluate potential effects on Northern Spotted Owls. Report prepared for the U.S. Fish and Wildlife Service, Lacey, WA and Yreka, CA. Olympia, WA: Washington Department of Fish and Wildlife. 32 p.
  17. Verhovek, Sam Howe (June 4, 2007). "To protect spotted owl, larger rival is targeted". Los Angeles Times.
  18. Barnard, Jeff (December 10, 2009). Experiment to test killing one owl to help another; Barred owl competing against spotted owl. The Associated Press
  19. Livezey KB (2010). "Killing barred owls to help spotted owls I: a global perspective" (PDF). Northwestern Naturalist. 91 (2): 107–133. doi:10.1898/NWN09-37.1. JSTOR 40856470. S2CID 11691153. Archived from the original (PDF) on May 25, 2017.
  20. Livezey KB (2010). "Killing barred owls to help spotted owls II: implications for many other range-expanding species". Northwestern Naturalist. 91 (3): 251–270. doi:10.1898/NWN09-38.1. JSTOR 40983223. S2CID 85425945.
  21. Friedman, Lisa; Einhorn, Catrin (January 13, 2021). "Trump Opens Habitat of a Threatened Owl to Timber Harvesting". The New York Times. ISSN 0362-4331. Retrieved January 14, 2021.
  22. Lewicki, Krista E.; Huyvaert, Kathryn P.; Piaggio, Antoinette J.; Diller, Lowell V.; Franklin, Alan B. (December 20, 2014). "Effects of barred owl (Strix varia) range expansion on Haemoproteus parasite assemblage dynamics and transmission in barred and northern spotted owls (Strix occidentalis caurina)". Biological Invasions. 17 (6): 1713–1727. doi:10.1007/s10530-014-0828-5. ISSN 1387-3547. S2CID 4798840.
  23. Holm, Samantha R.; Noon, Barry R.; Wiens, J. David; Ripple, William J. (November 27, 2016). "Potential trophic cascades triggered by the barred owl range expansion". Wildlife Society Bulletin. 40 (4): 615–624. doi:10.1002/wsb.714. ISSN 1938-5463.
  24. Diller, Lowell V.; Hamm, Keith A.; Early, Desiree A.; Lamphear, David W.; Dugger, Katie M.; Yackulic, Charles B.; Schwarz, Carl J.; Carlson, Peter C.; McDonald, Trent L. (February 17, 2016). "Demographic response of northern spotted owls to barred owl removal". The Journal of Wildlife Management. 80 (4): 691–707. doi:10.1002/jwmg.1046. ISSN 0022-541X.
  25. Hamer, Thomas E.; Forsman, Eric D.; Fuchs, A. D. & Walters, M. L. (April 1994). "Hybridization Between Barred and Spotted Owls" (PDF). The Auk. 111 (2): 487–491.
  26. Kelly, Elizabeth G.; Forsman, Eric D. (2004). "Recent Records of Hybridization Between Barred Owls (Strix Varia) and Northern Spotted Owls (S. Occidentalis Caurina)". The Auk. 121 (3): 806. doi:10.1642/0004-8038(2004)121[0806:rrohbb]2.0.co;2. ISSN 0004-8038.
  27. BARROWCLOUGH, G. F.; GROTH, J. G.; MERTZ, L. A.; GUTIÉRREZ, R. J. (March 16, 2005). "Genetic structure, introgression, and a narrow hybrid zone between northern and California spotted owls (Strix occidentalis)". Molecular Ecology. 14 (4): 1109–1120. doi:10.1111/j.1365-294x.2005.02465.x. ISSN 0962-1083. PMID 15773939. S2CID 23046067.
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