Northern saw-whet owl (Aegolius acadicus brooksi) COSEWIC update and status report: chapter 11

Technical Summary

Aegolius acadicus brooksi

Northern Saw-whet Owl brooksi subspecies – Petite Nyctale de la sous-espèce brooksi

Range of Occurrence in Canada:

British Columbia

Extent and Area Information

Extent of occurrence (EO) (km²)

10,000 km² Area of Haida Gwaii.

Specify trend in EO

Stable

Are there extreme fluctuations in EO?

No

Area of occupancy (AO) (km²)

Approximately 5,488 km². Amount of suitable habitat for occupancy on Haida Gwaii, including both fragmented regenerating forest (occupied at low density) and old forest (occupied at higher density).

Specify trend in AO

Decline; forest harvest creates unsuitable clearcut and dense forest habitat

Are there extreme fluctuations in AO?

No

Number of known or inferred current locations

Not applicable

Specify trend in #

Not applicable. Based on habitat loss through forest harvest

Are there extreme fluctuations in number of locations?

Not applicable

Specify trend in area, extent or quality of habitat

Decline in quality and quantity of habitat

Population Information

Generation time (average age of parents in the population)

Age at sexual maturity 1 year. Average age of parents likely 2-5 years.

Number of mature individuals

1,852 + 580

Total population trend:

Declining

 % decline over the last/next 10 years or 3 generations.

  • Last 15 years:  13%
  • Next 15 years:  9%
  •  Estimated based on rate of forest harvest throughout Haida Gwaii.

Are there extreme fluctuations in number of mature individuals?

Unknown

Is the total population severely fragmented?

No

Specify trend in number of populations

Only one population

Are there extreme fluctuations in number of populations?

No, only one population

List populations with number of mature individuals in each:

Not applicable

Threats (actual or imminent threats to populations or habitats)

Habitat loss: Nesting and foraging habitat declining due to forest harvest, which removes older forests with open structure and abundant nesting snags and produces dense forests which are clearly suboptimal for both foraging and nesting.
Introduced species: Raccoons and Red Squirrels are possible nest predators, while European Starlings are aggressive competitors for nest cavities. The large-scale habitat alteration caused by foraging Sitka Black-tailed Deer may have reduced densities of small rodents and invertebrates, both of which are important food sources.
Road kill: Birds are often hit by highway traffic between Skidegate and Tlell during the apparent movements to the shorelines during the fall.

Rescue Effect (immigration from an outside source)

Status of outside population(s)?

No outside populations

Is immigration known or possible?

Not possible; no outside populations

Would immigrants be adapted to survive in Canada?

Not applicable

Is there sufficient habitat for immigrants in Canada?

Not applicable

Is rescue from outside populations likely?

No

Quantitative Analysis 

Not done

Current Status

COSEWIC: Threatened (2006)
British Columbia CDC: Blue-listed

Status and Reasons for Designation

Status : Threatened

Alpha-numeric code: Met criteria for Endangered, C2a(ii) with its small population and projected habitat loss, but designated Threatened, C2a(ii) because of the presence of substantial protected areas.

Reasons for Designation: This is a distinct subspecies endemic to Canada, with a small world population (ca. 1,900 adults) restricted to the Queen Charlotte Islands. It is a forest specialist, preferring older forests with abundant nesting snags and an open understory in a landscape where such resources are continually becoming scarcer due to forest harvest. 

Applicability of Criteria

  • Criterion A: (Declining Total Population): not applicable
  • Criterion B: (Small Distribution, and Decline or Fluctuation): not applicable
  • Criterion C: (Small Total Population Size and Decline): Met criteria C2a(ii) for Endangered with fewer than 2,500 breeding individuals, continuing habitat decline and all individuals in one population.
  • Criterion D: (Very Small Population or Restricted Distribution): population too high
  • Criterion E: (Quantitative Analysis): not done.

 

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