Half-moon hairstreak (Satyrium semiluna) COSEWIC assessment and status report: chapter 6

Distribution

Global range

The range of Satyrium semiluna occurs from extreme southern interior British Columbia south to the east side of the Sierra Nevadas in central California and thence east to western Montana, eastern Wyoming and northwestern Colorado (Figure 2). The Alberta population belongs to a phenotype that extends to northwestern Colorado and westward through Nevada, Oregon and Idaho (Mattoon and Austin 1998). The taxonomic status and range of the British Columbia entity is unclear, but the southern limit may be in nearby northern Washington as evidenced by the presence of a different phenotype in Kittitas County (N. Kondla unpublished data).


Figure 2. Global and North American range of Satyrium semiluna

Global and North American range of Satyrium semiluna (see long description below).

Source: adapted from Opler (1999), S. Kohler (pers. comm.), N. Kondla (unpublished data), and A. Warren (pers. comm.). Note the disjunct population in SW Alberta.

Description of Figure 2

Map showing the range of Satyrium semiluna occurs from extreme southern interior British Columbia south to the east side of the Sierra Nevadas in central California and thence east to western Montana, eastern Wyoming and northwestern Colorado.

Canadian range

The Canadian range of S. semiluna consists of one known population in Waterton Lakes National Park and 11 known sites which may represent six populations of another subspecies in extreme southern interior British Columbia (Figure 3). The British Columbia population is contiguous with populations in Washington State (Guppy and Shepard, 2001). Less than 1% of the global distribution of S. semiluna is in Canada.

Literature reports indicate that the Half-moon Hairstreak in Canada has been recorded (under the name Sooty Hairstreak) from only a few areas in British Columbia and from Waterton Lakes National Park in Alberta (Bird et al. 1995, Bowman 1951, Guppy and Shepard 2001, Kondla 2003b, Layberry et al. 1998). The species is not known to occur in the area surrounding Waterton Lakes National Park (Kondla 2004a). A report of this species from the lower Fraser valley by Llewellyn-Jones (1951) is considered to be an error because the species has never been documented to occupy moist forest habitat anywhere in its range.

Prior to 2003, S. semiluna (then known as S. fuliginosum semiluna) was known in Canada from a historical collection by J. McDunnough in Waterton Lakes National Park in 1923 (specimen in Canadian National Collection). Kondla visited this area in 2003, noted a specimen in the park insect collection from 1967, and then discovered an extant population on an alluvial fan in the park (Kondla 2003a).


Figure 3. Known distribution of Satyrium semiluna in British Columbia

Known distribution of Satyrium semiluna in British Columbia (see long description below).

Note: due to map scale not all sites examined can be displayed as individual symbols. This is a new figure.

Description of Figure 3

Map showing known distribution of Satyrium semiluna in British Columbia: cross = previously known location confirmed in 2003; square = previously known location not resurveyed in 2003; circle = new locations found in 2003; triangle = locations surveyed in 2003 but no Hairstreaks found.


In British Columbia, the earliest known record for S. semiluna (also originally called S. fuliginosum) is from an unknown location in the vicinity of Osoyoos in 1895 (Canadian National Collection). Three specimens in the Royal British Columbia Museum were collected in 1898 and 1901 at an unknown location in British Columbia. Subsequently, there were a few collections from the vicinity of Keremeos in 1923; Anarchist Mountain in 1975, 1976, 1979, 1985 and 1990; and one sight record from Richter Pass in 2002. In 2003, Kondla conducted field surveys to confirm some past records and locate additional sites. This work resulted in the discovery of new sites in the vicinity of Kilpoola Lake, White Lake and Mt. Kobau, as well as the confirmation of the species’ presence at Richter Pass and Anarchist Mountain. An additional site near Keremeos Columns Provincial Park was reported by J. Fenneman (pers. comm.) in 2003.

The extent of occurrence and the area of occupancy of the single Alberta population are about 5 km2.

The extent of occurrence of the known British Columbia population is approximately 480 km2. The maximum potential area of occupancy of the British Columbia population is about 250 km2, based on a rough estimate of the amount of non-forested habitat within the extent of occurrence. Only a small portion of the total area of sagebrush/grassland habitat in British Columbia has been searched for the presence of S. semiluna. Field surveys in 2003 did not find the species in all apparently suitable habitat patches and yielded only seven occupied sites out of 33 searched. Existing information and observations suggest the species does not use steep terrain. Information is not available on how much of the non-forested area supports the lupine species presumed to be the larval food plant of the Hairstreak. In addition, the lupine is an abundant and widespread species in British Columbia, and its presence clearly does not determine the butterfly’s range in the province. Given these considerations, it is likely that the actual area of occupancy is a small percentage of the unforested area. A very rough preliminary estimate is that the maximum area of occupancy could be as little as 25 km2.

The extent of occurrence for the entire population of S. semiluna in Canada (Alberta and British Columbia populations combined) is 485 km2, and its area of occupancy is about 30 km2.

Page details

Date modified: