Spotted owl (Caurina subspecies) COSEWIC assessment and status report: chapter 12

Technical Summary

Strix occidentalis caurina

Northern Spotted Owl – Chouette tachetée

Range of Occurrence in Canada:
BC

Extent and Area Information

Extent of occurrence (EO) (km²) Estimated as occurring in
3.3% of the British Columbia land area (945,000 km²); based
on analyses by Harestad et al. (2004) and Pierce Lefebvre (2005) :
32,000 km²
Specify trend in EO :
Declining
Are there extreme fluctuations in EO?
No
Area of occupancy (AO) (km²). Estimated by multiplying standard home range size of 3.2 km² x 17 (number of active sites) :
Approx 54.4 km²
Specify trend in AO :
Declining
Are there extreme fluctuations in AO?
No
Number of known or inferred current locations
79 known locations since 1985 but only 14 were known to be active in 2006 and 2007 (J. Hobbs pers. comm.). 17 known locations with at least 1 adult owl in 2005; 14 sites in 2006 and 2007
Specify trend in # :
Declining
Are there extreme fluctuations in number of locations?
No
Specify trend in area, extent or quality of habitat. Habitat supply based on analysis by Chutter et al. (2007) :
Declining currently and forecast to decline for 20 years before stabilizing

Population Information

Generation time (average age of parents in the population) :
Ca. 8 years
Number of mature individuals :
19 known adults in 2007 based on an essentially complete count (J. Hobbs, pers. comm.).
Total population trend: Extirpation is forecast by this report
to occur between 2009-2012; based on known ages of known
owls and apparent lack of recent recruitment of young owls :
declining
% decline over the last/next 10 years or 3 generations.
Declined at about 10.4% annually 1992-2002 (67% decline over 10 years, 93% over 3 generations)
Are there extreme fluctuations in number of mature individuals?
No
Is the total population severely fragmented?
Yes
Specify trend in number of populations :
Number of occupied locations declining; most of these contain a single owl
Are there extreme fluctuations in number of populations?
No
List populations with number of mature individuals in each

Threats (actual or imminent threats to populations or habitats)

Very low population making it susceptible to stochastic events. High juvenile mortality and no or little current recruitment of young birds into the population. Habitat degradation and loss through logging and conversion of forests to urban/industrial uses. Habitat also susceptible to wildfires and insect outbreaks. Possibly at northern edge of range in BC and limited by climate. Low annual reproductive potential (pairs do not breed every year, fledge 1-2 young when do breed) but adults are long-lived.

Current low numbers, widely separated sites, fragmented habitat and lack of recruitment suggest extirpation in Canada by 2012.

Rescue Effect (immigration from an outside source)

Status of outside population(s)?
About 6,000 Northern Spotted Owls estimated to occur in the USA but populations there are declining.
Is immigration known or possible? Yes
Would immigrants be adapted to survive in Canada? Yes
Is there sufficient habitat for immigrants in Canada? No
Is rescue from outside populations likely? No

Quantitative Analysis

Extrapolation from current trends and population figures suggest extirpation by 2012.

Current Status

COSEWIC: Endangered

Designated Endangered in April 1986. Status re-examined and confirmed in April 1999, May 2000, and April 2008.

Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: A2ac; B2ab(i,ii,iii,iv,v); C1+2a(i), D1, E

Reasons for Designation: This owl requires old-growth forests for its survival and has suffered a catastrophic population decline over the past 50 years as habitat is lost and fragmented. With the severely depressed population, an additional threat is the recent arrival of the closely related Barred Owl as a breeding bird in B.C.; this species competes with and hybridizes with the present species. Its historical population of about 500 adult owls in Canada has been reduced to 19, and only 10 of these are in breeding pairs. All adults are old and near the end of their breeding age and there is no recruitment of young owls into the population. If current trends are not reversed, extirpation will likely occur within the next decade.

Applicability of Criteria

Criterion A: (Declining Total Population): Meets Endangered A2ac.

Criterion B: (Small Distribution, and Decline or Fluctuation): Meets Endangered B2ab(i,ii,iii,iv,v)

Criterion C: (Small Total Population Size and Decline): Meets Endangered C1+2a(i)

Criterion D: (Very Small Population or Restricted Distribution): Meets Endangered D1

Criterion E: (Quantitative Analysis): Endangered E (extirpation predicted by 2012)

Page details

Date modified: