Gold-edged gem (Schinia avemensis) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Search effort

During the past 75 years, there have been no records of Gold-edged Gems from the Aweme area in the Brandon sandhills. The species was described from specimens caught there by resident collector, Norman Criddle. Since Criddle’s time (approx. 1930), the only record of Gold-edged Gems from Manitoba is for four specimens collected in the Bald Head Hills (= Spirit Dunes) north of Glenboro in July and August 1958 (Appendix 1). The Spirit Dunes in Spruce Woods Provincial Park were visited by J. Troubridge and J.D. Lafontaine July 27-28, 2004. They discovered Gold-edged Gems resting on flowers and leaves of prairie sunflowers near the dune face in the early morning (J. Troubridge, pers. comm., 2004).

Virtually all active sand dunes in the Brandon Sandhills are now located within the Spirit Dunes section of Spruce Woods Provincial Park (David, 1977; Wolfe, 2001). Gary Anweiler visited the Spirit Dunes area on July 28, 2004. The entire boundary of the Spirit Dunes in Spruce Woods Provincial Park was walked and searched for Gold-edged Gems and colonies of the host plant. All areas of open, active sand areas in the dunes were also checked. Although colonies of Prairie Sunflower were scattered throughout the dunes, all were still in bud because of the lateness of the season, and no Gems were found. Anweiler returned to the area on August 4 and repeated the search of the same areas. At this time, the sunflowers were in the early stages of blooming (an estimated 0.25 percent of plants had blossoms) and Gold-edged Gems were active and were observed mating and visiting blossoms for nectar. Although colonies of the host plant were found scattered throughout much of the area, Gold-edged Gems were found only in a series of adjacent colonies of sunflowers near the active dune face. When the area was revisited on August 26-27, 2004, the prairie sunflowers were in full blossom, but no Gold-edged Gems were found, and it was concluded that the moth’s flight for the season was finished (G. Anweiler, unpublished data).

During the period July 28-August 4, roads criss-crossing the remainder of the Brandon Sandhills, Oak Lake Sandhills and Lauder Sandhills were driven to check for Gold-edged Gem habitat, i.e., open dunes and major blow-outs, as well as colonies of prairie sunflowers. No suitable habitat was located, and these areas appear unlikely to harbour colonies of Gems (G. Anweiler, unpublished data).

Although prior to the field work carried out in 2004 Gold-edged Gems had never been reported from Canadafrom outside the Brandon Sandhills area, potential Gold-edged Gem habitat (active dunes with colonies of the host) is known to occur more extensively in southwestern Saskatchewan and adjacent Alberta. The likelihood of Gold-edged Gems being present in other dunes in the southern Prairie Provinces was pointed out by Hardwick (1996). Anweiler examined several potential sand dune sites along the Yellowhead Highway for Gold-edged Gems and potential Gem habitat in late July, 2004, and checked the dunes at the east end of Good Spirit Lake for both Gems and prairie sunflower colonies (Table 1). A series of large open sand dunes in the northern section of the Great Sandhills south of Scepter - Prelate were visited and searched on August 6, 2004, as were a series of smaller open dunes north of the town of Burstall on the same date. A single worn female Gold-edged Gem found at the Burstall site was the only Gem located (Appendix 1).

No searches specifically for Gold-edged Gems have been carried out in Alberta. However, on July 29, 2004 during unrelated work, Chris Schmidt located a thriving colony of Gold-edged Gems in a small area of active sand blowouts on the edge of the Red Deer River north of Bindloss (B.C. Schmidt, pers. comm., 2004). In July of 2005, Anweiler located a second colony, in the Pakowki Lake dunes, also while doing unrelated work (Anweiler, unpublished).

Areas where searches were made for Gold-edged Gems and suitable Gem habitat in 2004 and 2005 are shown in Figure 8, and search results are summarized in Table 1.

Most of the largest and best potential habitat for the Gold-edged Gem has been searched. Additional small patches of potential habitat are scattered throughout the southern prairies, but have not been recently searched specifically for this species. Consequently, it is plausible that a limited number of additional sites with Gold-edged Gems may be found if directed searches are carried out at these as-yet unsurveyed sites. Any additional sites will be small and will also be declining.

Figure 8. Areas searched for Gold-edged Gems, 2004-2005

Figure 8. Areas searched for Gold-edged Gems, 2004-2005.
Table 1. Search effort results, 2004-2005.
No Location Date Hours
Effort*
Observations Observer
1 North of Chavin, Alberta 29-07-04
10
no S. avemensis Schmidt
2 Southwest of North Battleford, Saskatchewan 26-07-04
1
no S. avemensis or host Anweiler
3 Borden Bridge, Saskatchewan 26-07-04
0.5
no S. avemensis or host Anweiler
4 Good Spirit Lake, Saskatchewan 27-07-04
6
no S. avemensis or host Anweiler
5 Brandon-Oak Lake Lauder sandhills, Manitoba 30-07-04
12
no S. avemensis, scattered host Anweiler
6 Spirit Dunes, Manitoba 29-07-04
04-08-04
12
S. avemensisand host present Anweiler
7 Great Sandhills, south of Prelate, Saskatchewan 06-08-04
8
no S. avemensis or host Anweiler
8 Burstall Dunes, Saskatchewan 06-08-04
2
S. avemensisand host present Anweiler
9 Red Deer River, north of Bindloss, Alberta 29-07-04
3
S. avemensisand host present Schmidt
10 Pakowki Lake dunes, Alberta 21-07-05
4
S. avemensisand host present Anweiler

Abundance

There are no quantitative data available on population sizes for Gold-edged Gems. Fieldwork is needed to determine how much, if any, potentially suitable habitat supports Gold-edge Gem populations, how much of the habitat is occupied in areas where colonies are known to occur, and the number of Gems in the colonies over a period of more than one year. Obtaining meaningful population numbers even in occupied habitat is complicated by the small size and mobility of adult moths, as well as changes in numbers over the adult emergence period and from year to year. Numbers of moths are known to vary greatly from year to year due to weather and other factors (Pohl et al, 2004).

The occupied area at the Spirit Dunes, Manitoba site is quite small (estimated at about 50 ha in 2004), and the moths were fairly numerous where present. Although estimating the number of individuals of such a small, fast-flying and very active insect that has a patchy distribution within the available habitat is difficult, a reasonable estimate of adults at this site is thought to be in the range of 10-50 individuals per hectare, or 500-5,000 adults in 2004 (G. Anweiler, unpublished data). It should be noted that this figure is an estimate based on casual field observations by a single experienced individual, and not on any “hard” data.

In Saskatchewan, the single female specimen noted at the Burstall site was unexpected and may represent an individual colonizer from a more distant and as-yet undiscovered site. Although the area of dunes at the Bindloss, Alberta colony site is estimated to cover about 50 ha, the moths were only found concentrated in the centre of two active “blowouts” within these dunes, a much smaller area. A reasonable population estimate at this site is thought to be in the range of 100-500 adults in 2004 (C. Schmidt, pers. comm., 2004). At the Pakowki Lake dunes, few sunflowers were in bloom at the time and a search of all blossoms in the largest dune complex yielded about 15 Gold-edged Gems. However, it appeared that the hatch was just beginning, and the number of moths observed was likely a fraction of the total population at this locality. A reasonable estimate of the number of individuals is thought to be comparable to that at the similar-sized Burstall dune site (100-500 individuals).

Fluctuations and trends

Although there are few data with which to calculate population trends, several things are evident. First, Gold-edged Gems have persisted at the Manitoba site for at least 100 years, and have been present in southeastern Alberta since at least 1939. Prior to 2004 the colony in Manitoba was the only one known in Canada. The Gold-edged Gem is now known to be more widespread in the southern Prairie Provinces. Secondly, only a fraction of the active sand dunes present 100 years ago still persist. Although there is some evidence that this decline in active sand dune habitat has slowed (David, 1977), barring major changes in climate, this decline can be expected to continue. This large-scale decline in the active dune habitat of Gold-edged Gems over the past 100 years or more has likely resulted in a corresponding reduction in the size and number of Gold-edged Gem populations during that same period.

Rescue effect

The two Canadian populations of Gold-edged Gems, located along the southern Alberta-Saskatchewan border and in southwestern Manitoba (Figure 2) are separated by about 750 km of mostly unsuitable habitat, and the potential for exchange of individuals between them is likely nil.

The Gold-edged Gem is known from outside Canada at only three sites (two populations) in Colorado, approximately 1,200 km to the south (Figure 2). Consequently, the chances of individuals from Colorado re-colonizing Canada are also essentially nil. Furthermore, while individuals from Colorado might be able to survive in Canada, they show significant phenotypic differences (larger and darker in colour) and may be adapted to different conditions.

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