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Bird Habitat Conservation Toolkit

Image of Bird
Photo by US Fish & Wildlife Service
Wild Spotted Owl populations in BC have fallen from about 1,000 (historical estimate) to less than 30 individuals due to extensive habitat loss, fragmentation, & competition with Barred Owls.

Northern Spotted Owl

(Strix occidentalis)
Overview
status
SARAEndangered
British ColumbiaRed
SaskatchewanAbsent
Primary Habitat
Old coniferous (Douglas Fir)
Nest Type
Cavity/Broken top
Territory Size
2,000–3,000 ha
Nest Reuse
Common
Breeding Window
Jan
Feb
Mar
Apr
Apr
May
Jun
Jul
Aug
Aug
Sep
Oct
Nov
Dec
Stand-Level
Retention of large-diameter trees/snags with broken-tops, cavities, mistletoe brooms, etc.
Landscape-Level
Establishment of protected areas, particularly on wetter, less fire-prone sites.

Rather than attempting to synthesize the many region-specific recommendations outlined in recovery and BMP documents, this species account provides a broad overview of recommended practices for improving habitat quality for Spotted Owls. Forest managers are referred to region-specific strategies, detailed species recovery plans/requirements, and/or provincial biologists within their Forest District for targeted guidance (see Resources section at the end of this account).

Habitat Ecology

  • Spotted Owls reside in >100-year-old forests, and forest >140 years old is considered “superior.” Superior habitats are also conifer-dominated (preferably Douglas fir), multi-species stands with high stand complexity. Superior habitat is characterised by the following habitat features:1
  • Canopy closure >70% provides thermal cover and protection from bad weather.1
  • Broken-topped snags, cavities, mistletoe brooms, and in some cases abandoned raptor nests for nesting.1–3
  • Vertical and horizontal structural diversity (i.e., 3 or more shrub/canopy layers) and perches at several heights.1,2,4
  • Large-diameter trees (>75 cm dbh) and large snags, logs, and other downed woody material.2
  • Patchy understory vegetation totalling >40% cover, over a quarter of which is shrubs.1
  • Barred Owls have been expanding into the Spotted Owl’s range. Although closely related, the Barred Owl consistently out-competes Spotted Owls, and is thus considered a significant threat.2,5

Response to Forest Management

  • Habitat loss, fragmentation, and replacement of old forests with dense, even-aged forests are among the primary threats to the Spotted Owl.2
  • Fragmentation makes it more difficult for juvenile owls to safely disperse and establish new territories.2
  • Spotted Owls appear to avoid hard habitat edges but favour diffuse edges created by low-severity fire.6
  • Spotted Owl responses to stand thinning have been mixed; some studies have found negative effects of intensive thinning, while others have observed Spotted Owls in 10–50 year-old thinned and selectively harvested stands.5
  • In California and Oregon, Spotted Owls were observed using variable retention harvest units, irregular shelterwoods, and seed-tree harvests. This response was attributed to high woodrat densities within these harvest blocks, but the authors cautioned that a different response was expected in Douglas fir/western hemlock forests where northern flying squirrel is a more important prey item.7

Stand-level Recommendations

  • Within-block retention should be employed to promote the long-term structural diversity of harvested stands, including a combination of patches and dispersed retention,8 with an emphasis on large-diameter trees and snags with broken-tops, large horizontal branches, forks, cavities, mistletoe brooms, and evidence of decay.1,9
  • The above features should also be retained during salvage logging following low- and medium-severity fires.5
  • Large retention areas should be located in wetter areas and northern aspects, as these are more naturally resistant to fire.5
  • See Blackburn and Godwin (2004) for retention targets within management zones for different BEC subzones.3
  • Variable-density stand thinning may have short-term negative effects on northern flying squirrel abundances, but may provide long-term benefits to habitat quality and prey abundance (the oldest, largest trees and trees with deformities should be retained and snags should be created if not naturally available).5

Landscape-level Recommendations

  • The creation of Wildlife Habitat Areas to protect known Spotted Owl habitat is the main tool recommended for protecting and recovering this highly endangered species. The recommended reserve size is 3,600 ha, of which 2,400 ha should be old forest.9
  • In dry conifer forests that face a high risk of stand-replacing fires, there is cautious support for forest management that directly or indirectly promotes fire resistance.5
  • Fuel reduction treatments are discouraged within 125 ha around nesting and roosting habitats.10
  • Treatments may negatively impact local Spotted Owl habitat and/or nesting pairs in the short term.5,11
  • Potential treatments include retention of fire- and drought-resistant tree species, reducing stand basal area around these tress, and thinning of dense young stands that result from fire suppression.5
  • Natural fire refugia (wet areas, valley bottoms, perched water tables, etc.) may represent strategic areas for retention and reserves as they are more likely to resist future high-severity fire events.5

Resources

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