Sonora skipper (Polites sonora) COSEWIC assessment and status report: chapter 4

Distribution

Global range

The Sonora Skipper occurs in a roughly triangular area of western North America: from Baja California in the south, northeast to eastern Wyoming, northwest to southwestern British Columbia, and west in the United States to the Pacific coast. Within this general area, the species is represented by three major disjunct groups of populations plus two small populated areas (in southern California and northern Baja California), which in total constitute a relatively small portion of North America (Figure 2). The group of populations that occurs in Canada is apparently restricted to the northern Cascade Mountains and the adjacent Thompson Plateau of British Columbia and adjacent Washington (Figure 3).

Figure 2. Global range of Polites sonora.

Figure 2.  Global range of Polites sonora

Figure 3. Distribution of Polites sonora in southern British Columbia and adjacent United States (adapted from Guppy and Shepard, 2001).

Figure 3.  Distribution of Polites sonora in southern British Columbia and adjacent United States

Canadian range

The Canadian range of the Sonora Skipper is limited to south central British Columbia (Figure 4, see Appendix I for a list of Canadian specimen records). In the past, Sonora Skippers were known from three reasonably precisely defined locations, two on Crater Mountain and one at Twenty-minute Lake in Manning Provincial Park. A 1989 record exists from an undefined location in “Manning Park”, which may or may not be Twenty-minute Lake. The species was also known from one or two imprecisely defined locations in the “Hope Mountains”, a historical term referring to the Cascade Mountains between Hope and Princeton. Crater Mountain is in the Okanagan Range, and Manning Park and the “Hope Mountains” are in the Hozameen Range.  Both ranges are in the Cascade Mountains. The Canadian range of the Sonora Skipper is estimated to be less than 1% of the species’ global range.

Figure 4. Canadian distribution records of Polites sonora (square=previously known locations, not surveyed in 2003; circle=new locations found in 2003; triangle= locations surveyed in 2003 but no P. sonora found). Note: due to map scale, not all locations can be displayed as individual symbols.

Figure 4.  Canadian distribution records of Polites sonora

The distribution map in Layberry et al. (1998) incorrectly shows the record for “Hope Mountains” at the location of the town of Hope, as demonstrated by the Canadian Biodiversity Information Facility database having the coordinates of Hope associated with the record for the “Hope Mountains” specimen in the Canadian National Collection of Insects, Arachnids and Nematodes. The distribution map in Layberry et al. (1998) shows a record for Merritt on the Thompson Plateau for which the supporting information could not be located; this record is considered here to be a mapping error and is not included in Figures 3 and figure4. The “Merritt” dot is precisely north of the Manning Park dot, suggesting that the latitude was incorrectly entered into the mapping database for one of the Manning Park records.

Field work in 2003 by N. Kondla resulted in an additional location for the Sonora Skipper in the Wolfe Creek valley south of Princeton, and another in the Placer Creek valley east of Manning Park. No voucher specimens from these two new locations appear to have been deposited in a public collection, but some reside in the private collection of N. Kondla. The known Canadian range of the Sonora Skipper consists of portions of the Cascade Mountains from Manning Park east to Crater Mountain and the Thompson Plateau immediately south of Princeton.

The full distribution of the Sonora Skipper in Canada will only become known through a carefully designed inventory program. Additional unsampled suitable habitat that is not accessible by the road system likely occurs in this portion of southern British Columbia.  Based on the presently known distribution, the potential maximum extent of occurrence of the Sonora Skipper in Canada is in the order of 2100 km² (based on the area of the convex polygon that encompasses the geographic distribution of all known sites where the species is believed to be extant). However, this range consists primarily of obviously unsuitable alpine, forest and arid grassland habitats, with apparently suitable moist grassland habitat occurring on only a small fraction of the total range. Thus, the maximum current area of occupancy, based on a visual estimate of potentially suitable habitat from satellite images, is less than 5% of the potential maximum extent of occurrence, or about 100 km². However, the species does not occupy all apparently suitable habitats, as discussed in the next section. Kondla and Guppy estimate, from the limited existing data and based on their personal experience, that the area of occupancy is certainly less than 100 km² and may be less than 20 km².

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