Spotted owl

Source: Wikipedia, the free encyclopedia.
This article is about the bird indigenous to North America. For the bird indigenous to Asia, see Spotted owlet.

Spotted owl
Northern subspecies

Near Threatened  (IUCN 3.1)[1]
CITES Appendix II (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Strix
Species:
S. occidentalis
Binomial name
Strix occidentalis
(
Xántus, J
, 1860)
Subspecies

3, see text

The spotted owl (Strix occidentalis) is a species of

old-growth forests in western North America, where it nests in tree hollows, old bird of prey nests, or rock crevices. Nests can be between 12 and 60 metres (39 and 197 ft) high and usually contain two eggs (though some contain as many as four). It is a nocturnal owl which feeds on small mammals and birds. Three subspecies are recognized, ranging in distribution from British Columbia to Mexico. The spotted owl is under pressure from habitat destruction throughout its range, and is currently classified as a near-threatened species.[3][4]

Description

The spotted owl has an average length of 43 cm (17 in), wingspan of 114 cm (45 in), and weight of 600 g (1.3 lb). Its eggs are a little over 50 mm (2.0 in) long, and are white and smooth with a slightly grainy texture. The spotted owl is similar in appearance to the

interspecific hybrid owl referred to as a "sparred owl".[3][4]

Subspecies

The Gila Wilderness is home to the largest population of the Mexican subspecies.[5]

Distribution

The northern spotted owl has a nearly

Monterey County to northern Baja California. The Mexican spotted owl occurs in disjunct populations in mountain ranges and canyons of the Southwestern US (including Utah, Colorado, Arizona, New Mexico, and extreme western Texas), as well as in western Mexico (Sonora, Chihuahua, Nuevo León, and eastern Coahuila) through the Sierra Madre Occidental and the Sierra Madre Oriental.[6][7][8]

Habitat

Spotted owls occur in a variety of hardwood and coniferous forest habitats, although the species prefers closed-canopy, uneven-aged, late-successional, and old-growth forests. The Mexican subspecies may also make use of chaparral and pinyon woodlands, including areas in deep, steep-walled canyons with little canopy cover.[4][7][9] The California subspecies uses unlogged, complex early seral forests created by wildfire for foraging,[10][11] and more high-severity fire in a territory increases reproduction.[12][13]

Mexican spotted owl, Fort Huachuca, Arizona

Large trees seem to constitute preferred nesting and roosting habitat for all three subspecies,[4] and canopy cover greater than 40% (often greater than 70%) is generally sought out.[3][14] Substantial tall shrub cover is a common characteristic of spotted owl habitat.[15] Spotted owls can be found at elevations of 70–6,600 feet (21–2,012 m) for the northern subspecies, at 1,000–8,500 feet (300–2,590 m) for the California subspecies, and rather higher (6,000–8,500 feet (1,800–2,600 m)) for the Mexican spotted owl. All subspecies appear to value the proximity of water sources.[4]

Ecology

Home range and density

Spotted owl home ranges are generally large but of variable size, with extents of 661–14,169 acres (2.67–57.34 km2), depending on subspecies, habitat, and prey availability. Home ranges are smaller in the breeding season than in the nonbreeding season, and females have larger home ranges than males.[4]

Density of spotted owl pairs within suitable habitat also depends on specific habitat quality and location, varying between 0.022 owls/km2 in pinyon-juniper woodlands of the Sacramento Mountains[8] and 1.049 owls/km2.[16]

Nesting

Spotted owls do not build their own nests, instead making use of cavities found in trees, deadwood, and snags, and the sites of abandoned raptor or squirrel nests. Some nest sites are used repeatedly.[4] High-quality (consistently occupied and reproductive) breeding sites remain occupied after wildfire and post-fire salvage logging, while lower quality sites that are inconsistently occupied and reproductive are more likely to be abandoned after fire and salvage logging.[17] Spotted owls most often choose the same type of cover selected for nesting sites for daytime roosting.[18]

Breeding

The spotted owl's breeding season occurs from early spring to late summer or fall, with prelaying behaviors such as preening and roosting together starting in February or March.[4]

Spotted owl pairs are monogamous and rarely re-nest after failed breeding attempts.[6] The species does not normally breed every year, with average breeding probability being 62%. Young owls may start breeding at an age of one year but two years or older is more common.[18] Normal clutch size is two eggs but may reach four on rare occasions. The female sits on the eggs and cares for the young, while the male provides food for them. Egg incubation times of about a month have been reported from western Oregon;[18] time from fledging to independence of chicks is between three and four months.[4] Once independent, juveniles disperse in late summer to fall, in the northern range often settling into a wintering range before seeking out breeding territories in the spring. Dispersal range is often less than 19 mi (31 km).[19]

Lifespan and mortality

Spotted owls are long-lived and maximum ages of 16 or 17 years have been documented in the northern subspecies. The average annual survival rate is usually in excess of 80% for adults, although it is considerably lower for juveniles, which have an average annual survival rate of 21–29%.[4] In New Mexico, the survival rate for fledgling Mexican spotted owls can be as low as 11%.[4] The most common causes of mortality are predation, starvation, and possibly disease.[4]

Various birds and mammals such as the fisher (Pekania pennanti) are among the predators of eggs and young spotted owls, American goshawks (Accipiter atricapillus), crows may prey on juvenile spotted owls, while great horned owls (Bubo virginianus), red-tailed hawks (Buteo jamaicensis), and golden eagles (Aquila chrysaetos) are likely predators of both juveniles and adults. Great horned and barred owls compete with spotted owls for food and space in some areas. Barred owls have a negative effect on northern spotted owl survival and fecundity.[4]

Diet

Spotted owls are

snowshoe hares (Lepus americanus), rabbits,[20] and several species of squirrels. Bats and non-mammalian prey species are taken to a lesser extent, including birds (smaller owls, jays, woodpeckers, and passerines,[20] including various songbirds), amphibians, reptiles, and insects.[4]

Conservation

The

near threatened with a decreasing population trend.[1] NatureServe considers the species Vulnerable.[21] All studies assessing the species' population trend have found populations to be in decline. Habitat loss due to timber harvesting is generally recognized as the main threat.[4] One study reported that competition with the barred owl is also a major contributor to the decline of the spotted owl.[22] Forest and spotted owl management documents often state that severe wildfire is a cause of recent declines in populations of spotted owls, and that mixed-severity fires (5–70% of burned area in high-severity patches, with >75% mortality of dominant vegetation) pose a primary threat to spotted owl population viability, but a systematic review and meta-analysis found fires created more benefits than costs for spotted owls.[12][13]

The northern spotted owl and Mexican spotted owl subspecies are listed as threatened in the United States under the

U.S. Fish and Wildlife Service (USFWS) after 20 years of attempts by environmental groups to get it listed. The Coastal-Southern California distinct population segment (DPS) is proposed for endangered status, while the Sierra Nevada DPS is proposed for threatened status with a 4D rule exception.[23] The northern spotted owl was one of a few cases where the "God committee", a provision of the Endangered Species Act, has been invoked to decide whether or not to open up more federal forest for commercial logging.[24] In a battle between two federal agencies, the Bureau of Land Management, and the Fish and Wildlife Service, the committee ruled for the exemption of 1,700 acres from the ESA. The legal battle went on at different levels[clarification needed], creating a complex case study in environmental law.[25]

Each subspecies of the spotted owl is a frequent subject of disagreement between

cattle grazers, developers, and other organizations whose activities can affect forest conservation. In February 2008, a federal judge reinforced a USFWS decision to designate 8,600,000 acres (35,000 km2) in Arizona, Utah, Colorado, and New Mexico as critical habitat for the Mexican spotted owl. The decision was challenged by the Arizona Cattle Growers' Association, but the decision was upheld on appeal.[26]

By 2006, the northern spotted owl was reported to be in rapid decline in the northernmost part of its range, with a 7.2% annual decline across northern Washington and southwestern British Columbia. Fewer than 30 breeding pairs were thought to exist in Canada in 2006, and some experts have predicted the imminent extirpation of the species from Canada.[27]

An experiment sanctioned by the USFWS investigated the suitability of protecting the spotted owl by controlling its competitor, the barred owl. Work began in 2009 by removing populations of barred owls in designated areas. The studies found that in the absence of barred owls, the population of spotted owls did not decline, and were able to bounce back.[28]

References

Public Domain This article incorporates public domain material from Strix occidentalis. United States Department of Agriculture.

  1. ^
    doi:10.2305/IUCN.UK.2020-3.RLTS.T22689089A180937862.en
    . Retrieved 19 November 2021.
  2. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  3. ^ a b c Gutiérrez, R. J.; A. B. Franklin & W. S. Lahaye (1995). "Spotted Owl". bna.birds.cornell.edu. Birds of North America Online. Retrieved 2016-09-12.
  4. ^ a b c d e f g h i j k l m n o "Strix occidentalis". US Forest Service. Retrieved 25 November 2015.
  5. ^ Mexican Spotted Owl Recovery Program at U.S. Fish and Wildlife Service.
  6. ^ a b Gutierrez, R. J.; Franklin, A. B.; LaHaye, W. S. (1995). "Spotted owl (Strix occidentalis)". In Poole, A.; Gill, F. (eds.). Birds of North America No. 179. Philadelphia, Pennsylvania: The American Ornithologists' Union. pp. 1–28 – via The Academy of Natural Sciences of Philadelphia.
  7. ^
    ISBN 1-55963-458-8
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  8. ^ a b Ward Jr., James P.; Franklin, Alan B.; Rinkevich, Sarah E.; Clemente, Fernando (1995). Mexican spotted owl recovery plan, volume 2—Technical supporting information (Report). Albuquerque, New Mexico: U.S. Department of the Interior Fish and Wildlife Service.
  9. ^ Gutierrez, R. J.; Verner, Jared; McKelvey, Kevin S.; Noon, Barry R.; Steger, George N.; Call, Douglas R.; LaHaye, William S.; Bingham, Bruce B.; Senser, John S. (1992). Verner, Jared; McKelvey, Kevin S.; Noon, Barry R.; Gutierrez, R. J.; Gould Jr., Gordon I.; Beck, Thomas W. (eds.). The California spotted owl: a technical assessment of its current status (PDF). Albany, California: U.S. Department of Agriculture Forest Service: Pacific Southwest Research Station. pp. 79–98. PSW-GTR-133. Archived from the original (PDF) on 2017-06-06.
  10. S2CID 67831139
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  11. doi:10.1002/jwmg.21112
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    doi:10.1002/ecs2.2354
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    doi:10.1002/ecs2.3310
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  16. ^ Diller, Lowell V.; Thome, Darrin M. (1999). "Population density of northern spotted owls in managed young-growth forests in coastal northern California" (PDF). Journal of Raptor Research. 33 (4): 275–286.
  17. S2CID 85676545
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    JSTOR 3830695
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  20. ^ a b "Spotted Owl". The Peregrine Fund. Retrieved 2023-01-20.
  21. ^ "NatureServe Explorer 2.0". explorer.natureserve.org. Retrieved 10 November 2022.
  22. hdl:10919/97903
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  23. ^ U.S. Fish & Wildlife Species Assessment Team; Sacramento Fish and Wildlife Office (23 February 2023). "Endangered and Threatened Wildlife and Plants; California Spotted Owl; Endangered Status for the Coastal-Southern California Distinct Population Segment and Threatened Status With Section 4(d) Rule for the Sierra Nevada Distinct Population Segment". Federal Register. 88 (36): 11600–11639. 88 FR 11600
  24. ^ Wilcove, David; Bean, Michael (7 April 1992). "Avoid This Trap, Mr. President: Endangered species: The 'God committee' will rule on saving owls vs. cutting timber". Los Angeles Times.
  25. doi:10.58948/0738-6206.1581
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  26. ^ Rotstein, Arthur H. (8 February 2008). "Habitat for Mexican Spotted Owl to Stand". USA Today. Retrieved 10 January 2013.
  27. S2CID 128839939
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  28. ^ Arnold, Catherine (29 Feb 2016). "Invasive Species: California Biologists Are Killing Invasive Barred Owls To Help Spotted Owls". Retrieved 29 Feb 2016 – via Nature World News.

External links

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