Sonora skipper (Polites sonora) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

Locations known to be occupied by the Sonora Skipper include a grassy roadside area along the upper Ashnola River, mesic grassy forest openings on the northeast slope of Crater Mountain (elevation 1160 and 1670 metres), a moist agricultural meadow south of Princeton, and moist grassy logged areas near Placer Creek. On Crater Mountain near Keremeos, the habitat description of “dry grassy slopes” given in Guppy and Shepard (2001) is poorly phrased and, according to C. Guppy, was intended to contrast with the distinctly wet meadow habitats of the two Polites species discussed in the pages immediately prior to the treatment of P. sonora, rather than referring to truly “arid” grassy slopes. Kondla conducted comparative searches of nearby moist, mesic and dry habitats on three days (dates and locations not available) in 2003 at and near the Placer Creek population. The species was only seen in the moist and mesic vegetation types. Figures 5 and figure 6 illustrate two habitat patches occupied by the Sonora Skipper in 2003.

Figure 5. Sonora Skipper habitat in an agricultural field near Princeton.

Pyle (2002) describes Polites sonora habitat in Washington and Oregon as “flowery meadows, clovery pastures, forest lanes and roadsides, stream banks, grassy clearings in woodland, and swampy springs”; “boggy edges of logging roads”; “an artificial meadow at an abandoned logging camp”; and “subalpine turf”. Layberry et al. (1998) report the habitat as “moist grassy areas from low elevations high into the mountains”.  The few known Canadian locations range in elevation from 765 m to 1700 m.

Figure 6. Sonora Skipper habitat in a logged riparian area SW of Princeton.

The detailed habitat requirements of the Sonora Skipper are unknown, but it is significant that this species does not occur in all visually suitable habitat and is sometimes present in only a small portion of an occupied habitat patch. According to J. Pelham (pers. comm.), “colonies can be extremely colonial and local” in Washington State. This was also the case at the two Canadian locations examined by Kondla in 2003. At Wolfe Creek, the skipper was present in only one of the four visually suitable habitat patches searched. Several hours of searching revealed that within the occupied habitat patch of approximately 105,000 m², the skippers were present only in an area of approximately 400 m² (0.4%). A similar situation occurred at Placer Creek.

Habitat trends

The total area of suitable habitats for the Sonora Skipper may have increased in response to the removal of closed canopy forests. Tree removal by agriculture and forestry generally creates temporary habitats with a longevity measured in decades. However, forest ingrowth is a significant factor reducing the size and number of meadows available to the Sonora Skipper within the butterfly’s known range in British Columbia. Wildfire control may have decreased the amount of suitable natural habitat by increasing the total area occupied by mature forests. Turner and Krannitz (2000) have documented ingrowth of trees into meadows and grasslands, and point out that there is likely a positive interaction between grazing and fire suppression that hastens forest ingrowth. Gayton (2003) also notes that the areas near sites where the Sonora Skipper has been found are biodiversity hotspots with high species richness and concentrations of species at risk within areas undergoing rapid grassland changes. Within the range of the skipper, patches of suitable habitat are continually created and lost. Hence the net benefit of human-created habitats depends on the rate at which habitat patches are created and colonized compared to the rate of loss of habitat patches to more intensive agricultural activity or forest regeneration.

Habitat protection/ownership

If the populations of Sonora Skippers previously reported from Manning Provincial Park and Cathedral Provincial Park still exist, they may be protected from infrastructure development and some other human activities (depending on park development), but may be threatened through forest and shrub encroachment. The other known locations are on provincial Crown land and private land and presently lack protection.