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COSEWIC Assessment and Status Report on the White Flower Moth (Schinia bimatris) in Canada

Habitat

Habitat requirements

The habitat associations and requirements of the Manitoba population of S. bimatris appear to be restricted to active sand dunes and blowouts (Figure 4). Stabilized dune habitat should be surveyed in Spruce Woods Provincial Park to determine if this habitat type is also suitable. Stabilized sand dunes, more heavily vegetated than the Spirit Dunes, include Souris, Oak Lake, Lauder, Routledge and St. Lazare sand hills in southwestern Manitoba (Wolfe 2001).

Figure 4. Schinia bimatris habitat, Spirit Sand Dunes, Spruce Woods Prov. Park, Manitoba. C. Schmidt photograph.

Figure 4.Schinia bimatris habitat, Spirit Sand Dunes, Spruce Woods Prov. Park, Manitoba. C. Schmidt photograph

Spruce Woods Provincial Park is within the Aspen Parkland Ecoregion (Gauthier et al. 2001). The local surface geology is characterized by the Brandon Sand Hills, which were formed by glaciolacustrine sediments of glacial Lake Agassiz and were re-worked by aeolian processes following deglaciation (David 1977).

In the southeastern U.S., S. bimatris inhabits longleaf pine woodlands (J. Slotten and V.A. Brou Jr., pers. com.) which are characterized by an open, herbaceous understory historically maintained by frequent fires. Longleaf pine woodlands are an endangered ecosystem in the U.S. and are home to a large number of amphibians and reptiles of conservation concern (Noss 1989).

Trends

The Spirit Sand Dunes (Figure 4) cover an area of about 5 km², consisting of about 0.2 km² of active dunes (Vance & Wolfe 1996). It is thought that the proportion of active dunes has remained fairly stable since the 1960s, prior to which the extent of active dunes was much greater, covering at least 145 ha in the 1920s, with a decline of about 10 to 20% per decade over the past 80 years (Figure 4b; Vance & Wolfe 1996). This decline in active dune habitat likely represents a decline in moth population size. Recent evidence suggests increases in dune activity associated with increased climate warming and aridity (Wolfe 1997), but does not necessarily represent an increase in suitable habitat for the White Flower Moth. In historic times, the Spirit Sand Dunes were kept active by natural disturbances, such as bison grazing and prairie fires. Although the stabilization of these dunes by vegetation overgrowth may have stopped in recent years and may even be reversing, dune re-activation may now be due to higher temperatures and drought conditions resulting from climate change. Although this dune re-activation may produce more active dune habitat, it is possible that the moth needs the more humid conditions that occurred in the past. If so, the current shift toward hot, arid conditions may not provide suitable habitat for the moth (J. Duncan, pers. com.).

Although sand dunes are widespread in the southern prairie provinces, dune blowouts are limited and occur primarily in the Middle Sand Hills, Alberta, Great Sand Hills, Saskatchewan and to a lesser extent in the Brandon Sand Hills, Manitoba (Wolfe 1997).

The absence of historical and recent records of S. bimatris from similar habitats in Alberta and Saskatchewan, makes it unlikely that this species is more widespread in Canada. Furthermore, the Brandon Sand Hills occur in a humid to sub-humid region, whereas prairie dunes elsewhere in Canada are characterized by a much more arid climate (Wolfe 1997).

Directed sampling should be carried out in dune habitats, particularly those supporting the suspected host plant. The Minot Dune Field in North Dakota may be the most likely nearest adjacent population, approximately 200 km to the southwest (Forman et al. 2001).

Figure 4b. Aerial photographs of the Spirit Dunes, Manitoba, showing recent dune stabilization. Active blowouts are visible as light areas, in 1990 (A) and 1928 (B) & 1947 (C). [Reproduced from Wolfe et al. (2000) with permission of the author.]

Figure 4b. Aerial photographs of the Spirit Dunes, Manitoba, showing recent dune stabilization. Active blowouts are visible as light areas, in 1990 (A) and 1928 (B) & 1947 (C). [Reproduced from Wolfe et al. (2000) with permission of the author.]

Protection/ownership

The habitat of the Manitoba population is encompassed by Spruce Woods Provincial Park and C.F.B. Shilo, under provincial and federal jurisdiction, respectively. The extant population of S. bimatris is entirely encompassed by Spruce Woods Provincial Park and is therefore legally protected.