Northern spotted owl (Strix occidentalis caurina) recovery strategy: chapter 5

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2. Distribution

2.1 Global Range

The Northern Spotted Owl[1], Strix occidentalis caurina, is the only subspecies of Spotted Owl found in Canada. This subspecies is distributed from the southwest mainland of British Columbia through western Washington, western Oregon and the coast ranges of California to San Francisco Bay (Figure 1). Although the current range is similar to the historic range, the distribution and abundance of Spotted Owls within this range has been significantly altered (USDI 1992).

2.2 Canadian Range

The entire known Canadian population of the Spotted Owl occurs in the southwest mainland of British Columbia, extending from the international border north about 200 km to Carpenter Lake, and about 160 km from Howe Sound in the west to the Cascade Range in the east (Figure 2). Changes in range are difficult to determine because of limited and poorly distributed inventory efforts in the past. For example, recent surveys have found Spotted Owls further north and east (e.g., Carpenter Lake) than previously known. However these areas were not previously surveyed and it is unknown if this represents a recent expansion or whether they have always occurred there. As all potential habitat has not been surveyed, the full extent of the range of Spotted Owls in British Columbia is still uncertain. Spotted Owls formerly occurred in much of the lower Fraser River valley, but are now absent because suitable habitat has been largely replaced by human development. Surveys conducted between 1992 and 1997 in the Squamish/Whistler area did not detect any Spotted Owls, suggesting that they were no longer present during that time despite historic records (Blackburn and Godwin 2003).

2.3 Proportion of Global Distribution in Canada

Approximately 8% of the global range of the Spotted Owl is located in Canada, and all of that lies within British Columbia (Figure 1).

2.4 Distribution Trend

The overall distribution of the Spotted Owl in British Columbia is unknown because inventories have not been conducted to determine the full extent of either the original or current ranges. Two early published auditory records (Laing 1942, cited in Campbell et al. 1990) of Spotted Owls in the Powell River area are well outside its current range to the west, which suggests a decrease in their range. But these records were considered unconvincing and not accepted as confirmed records in The Birds of British Columbia (Campbell et al. 1990) or by the Spotted Owl Recovery Team (SORT; Dunbar and Blackburn 1994). Yet there is some concern for a current decline in the range of Spotted Owls because they have not been detected in the most southwestern portion of their range (e.g., Capilano watershed) since 2000. On the other hand, in recent years, new detections of Spotted Owls have been confirmednortheast of their previously known range. However, these detections do not necessarily support a range expansion because earlier inventories for this area are not available for comparison. In summary, the overall distribution trend of the range of the Spotted Owl in British Columbia appears relatively unchanged. There is potential for further expansion of the known range as the owls expand into new areas, but at the same time, the risk of collapse remains in other portions of the range where owls are no longer being detected.

[1]Unless specified, the term “Spotted Owl” in this document will refer to the Northern Spotted Owl.