Potential South Coast Occurrence Range
Distribution: The Northern spotted owl subspecies represents the northern end of this species group in North America. The species is a permanent resident throughout its North American range, following old growth and mature coastal forests from southwestern British Columbia to southern California, and along the southern Rocky Mountains from central Colorado to central Mexico. The range in BC is restricted to the South Coast mainland, as far north as Anderson Lake, east to Manning Park and west to the Squamish watershed. In Metro Vancouver, it may still occur in the drinking watersheds (Capilano, Seymour, Coquitlam). The caurina subspecies is extremely imperiled in BC and in 2006 was down to at least 22 individuals (6 breeding pairs). The species as a whole is facing significant declines in the extent of its range in North America (Chutter et al 2006).
Description: The northern spotted owl is a medium-sized, round-headed owl lacking ear tufts. Plumage is generally brown interlaced with buff tipped (spotted) with white. Sexes are alike; however, females are slightly larger than males. Juveniles can have somewhat less distinctive markings.
Diet: Spotted owls feed primarily on small mammals associated with old-growth and mature coastal forests such as northern flying squirrels, bushy-tailed woodrat, red-backed voles and deermice.
Look’s Like? This species is most likely to be confused with the more common naturalized barred owl, a close, competitive relative with which it may be hybridizing (Sutherland et al 2007). The barred owl lacks the characteristic white tipped breast and belly plumage, instead feathers are streaked (barred) over a light buff breast and belly. Juveniles between the two species can have somewhat less distinctive markings. Members of the Strix genus have large dark brown eyes, a key difference from the other owls that they may co-occur with which generally have yellow eyes.
Primary Habitat: As with its prey species the spotted owl is an old growth-mature forest specialist, and forages and roosts in late seral (older successional) stands that have >50% canopy closure. In wet forest areas, this species generally uses stands dominated by conifers, though they may use mixed conifer-hardwood stands. Pure hardwood stands are not used in the winter, but they may be used for foraging and roosting in the summer. In drier forest areas, the owls use pure fir or mixed conifer forests containing at least 20% fir. These preferences reflect the availability of their most important prey species, the flying squirrel, which feeds on fungi growing on Douglas-firs.
Secondary Habitat: While this species is primarily old-growth forest dependent, mature second growth features are utilized where sufficient prey base and structural diversity are present.
Critical feature: The northern spotted owl nests in large (>30 cm dbh, but preferably >50 cm dbh) trees in old growth stands within tree cavities or abandoned hawk or crow nests. Trees with broken tops, tree cavities resulting from heart rot, and platform nests built by other species are important habitat features. Breeding begins at two or three years of age. This species usually mates for life and uses the same nest site in subsequent years, though they do not breed every year. Spotted owls are easily subjected to heat stress and respond to variations in temperature by moving within the canopy to more favourable microclimates. In summer, when temperatures are warmer, roosts tend to be in cool, shady areas. Their narrow preferred range of ambient temperature may be one of the reasons they strongly select mature and old forest habitats (Gutiérrez et al. 1995).
Seasonal Life Cycle
Jan / Feb / Mar / Apr / May / Jun / Jul / Aug / Sep / Oct / Nov / DecHabitat Guild: Upland and riparian old growth and late mature coniferous forests, mature deciduous and mixed forests.
Threats (based on Chutter et al 2004 and Sutherland et al 2007)
q Fragmentation of forest habitats, loss of preferred nesting features and prey availability (tied to forest structure) are considered the most significant threats.
q Spotted Owl populations naturally have low fecundity and low juvenile survivorship (normally offset by high survivorship of adults). Effects of low recruitment on population growth rate may be exaggerated because of the small population and its increasingly fragmented distribution. These effects may hinder chances of the population’s recovery.
q Disturbance (especially due to industrial activity like road building and logging) may exacerbate low juvenile survival and breeding success.
q Predation on chicks by other raptors (e.g. great horned owl) and inter species competition and hybridization with barred owl.
q Bio-accumulative impacts on breeding success from use of pesticides in forest management (eggshell thinning).
q Potential impacts from disease vectors (i.e. West Nile virus).
Conservation Objectives
q Identify and conserve critical habitat - support habitat features that provide for widely dispersed breeding territories and nesting preferences for remote forested regions with extensively forested canopies.
q Determine the minimum amount and distribution of critical habitat needed
to maintain a stable, self-sustaining population distributed throughout the species’
natural range.
q Enhance wild populations through a captive breeding program to re-establish distribution throughout that range to a level (250 individuals) that permits the removal of the endangered status. (This would entail either removing all or some of the remaining Spotted Owls from the wild or to remove four adults of each sex and all known juveniles from the wild – yet to be determined).
q Undertake control measures to reduce inter-species competition and predation (e.g. barred and possibly great-horned owl).
q Re-evaluate seral structure needs (e.g. dependency on old-growth and mature second growth stands and amend harvest plans accordingly. Under IWMS, a limited number of Wildlife Habitat Areas may be established on provincial Crown forest and/or range land, including such areas not covered by the SOMP (Province of British Columbia 2003). Wildlife Habitat Areas of sufficient size and quality have the potential to protect owl territories.
Management Practices Check List
q Assess, inventory and monitor using methodology setout in the RISC standards # 11 Inventory Methods for Raptors (Version 2.0 http://ilmbwww.gov.bc.ca/risc/pubs/tebiodiv/raptors/version2/rapt_ml_v2.pdf
q Apply methods as set out in Best Management Practices for Raptor Conservation during Urban and Rural Land Development in British Columbia. http://www.env.gov.bc.ca/wld/documents/bmp/raptor_bmp_final.pdf
q Territory establishment by Spotted Owls appears to be limited by the amount, quality, and distribution of habitat found within the landscape. Higher fecundity and adult survivorship is associated with larger amounts of suitable habitat in areas surrounding the nest area (Bart 1995; see Meyer et al. 1998).
q Avoid activities that result in a reduction in stem density, canopy volume and habitat quality in forested stands (e.g. under storey brushing, patch cutting and clear-cutting).
q Spotted Owls are non-migratory, home ranges, particularly in the northern parts of their distribution, are very large (Gutiérrez et al. 1995). Preliminary home range size estimates from telemetry studies in British Columbia appear to be consistent with estimates from Washington i.e. 2100 to 4000 ha (reviewed by Gutiérrez et al. 1995).
q During breeding season owls concentrate activities closer to their nests, than in the non-breeding season (Carey et al. 1990). Natal rearing areas were assessed at 400 ha (Sutherland et al 2007).
q Connectivity among subpopulation clusters is considered essential to maintain a population’s viability (Lamberson et al. 1994.)
q Sightings, specimens, or observations of activities threatening its habitat should be reported to the regional Species at Risk Biologist at the Ministry of Environment office.
Mitigating Impacts
q Maintain the hierarchical structure of core zones and home range zones e.g. nest sites, nest areas, post-fledging area and foraging areas. Core zones should have limited access and no disturbance.
q The general wildlife measures (GWMs) for the northern spotted owl (as an identified wildlife) include recommendations to maintain or restore at least 67% of the gross forested area within a designated Wildlife Habitat Area for this species, of which 75% should be maintained or restored as superior habitat ( >140 years, >19.4 m tall and 1370 m).
q Distribute the 67% suitable habitat into large non-fragmented patches >500 ha that are connected by movement corridors of suitable habitat that are a minimum of 1 km wide.
Main References & Literature Cited:
A Field Guide to Species at Risk in the Coast Forest Region of British Columbia: Published by: International Forest Products Limited and Ministry of Water, Land and Air Protection. 2003.
Accounts and Measures for Managing Identified Wildlife – Accounts V. 2004 –
http://www.env.gov.bc.ca/wld/frpa/iwms/accounts.html
Recovery Strategy For The Northern Spotted Owl (Strix occidentalis caurina) in BC. Chutter, M.J. et al. 2004. http://www.sararegistry.gc.ca/virtual_sara/files/plans/rs_spotted_owl_caurina_1006_e.pdf
A Framework to Support Landscape Analyses of Habitat Supply and Effects on Populations
of Forest-dwelling Species: A Case Study Based on the Northern Spotted Owl. G.D. Sutherland et al. B.C. Min. For. Range, Res. Br., Victoria, B.C. Tech. Rep. 038. 2007
http://www.for.gov.bc.ca/hfd/pubs/Docs/Tr/Tr038.pdf
Northern Spotted Owl Population Enhancement and Recovery in British Columbia. Proposed Five-Year Action Plan. SOPET. March 2007. http://ilmbwww.gov.bc.ca/sarco/so/files/SOPET_Proposed_5year_Action_Plan-20070330.pdf
BC Species & Ecosystems Explorer (BC Conservation Data Center Summary Report) http://www.env.gov.bc.ca/atrisk/toolintro.html
NatureServe Explorer - http://www.natureserve.org
Committee on the Status of Endangered Wildlife in Canada: http://www.cosewic.gc.ca/
Image credits:
SO – Rod Gilbert
Habitat – Alex Isenberg
Field Guide to Select Species of Conservation Concern for the South Coast of British Columbia
Northern Spotted owl - Draft 2008