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COSEWIC assessment and update status report on the mormon metalmark in Canada

Habitat requirements

The Mormon Metalmark is a butterfly of arid regions.  It appears to be associated with hillsides, dunes, and embankments on sandy or gravelly soils where the buckwheat larval hostplants grow (Opler 1999, Pyle 2002).  In California, Arnold and Powell (1983) found the buckwheat hostplant (E. nudum auriculatum Benth.) requires a moderate disturbance regime in order to attain the moderate to high densities that the metalmark (in this case Apodemia mormo langei J. A. Comstock) appears to require. They also found that metalmarks require large, mature plants for oviposition, presumably to provide adequate food and protection for the butterfly’s immature stages.

In both Saskatchewan (Hooper 2002) and British Columbia (St. John 2001), metalmarks are closely associated with unstable slopes, seldom straying onto flats even when the latter support significant hostplant populations (Figs. 5 and 6). In British Columbia, dense populations of the hostplant occur only on land that has been subject to disturbance, usually along road or railway corridors.  Steeply sloping sites with gravely or sandy soils also provide enough soil disturbances from natural erosion to provide suitable conditions for dense populations of Eriogonum niveum Dougl.  In Saskatchewan, the butterfly is also associated with arid hillsides, in this case supporting significant populations of Eriogonum pauciflorum Pursh. 

Adult metalmark butterflies also require a nectar source, and this is provided by the buckwheat hostplants throughout much of the flight season.  Common rabbitbrush Ericameria nauseosus Pall. also appears to be an important nectar source in both provinces, especially at times when the hostplant is not in bloom.  Adult nectaring appears to be restricted to these two plant species even though several other plants may be in bloom (St. John Pers. obs.).

All metalmark colonies in British Columbia occur in the Similkameen River drainage in sagebrush steppe in the hottest and driest biogeoclimatic subzone.  This bunchgrass subzone covers approximately 366 km2 in the Okanagan and Similkameen regions combined; and 117 km2 in the Similkameen drainage.  Most habitat units within this subzone are not suitable for Mormon Metalmarks.  The total area of the 15 colony sites identified since 1995 cover approximately 8 ha (Dyer 2002).  Given the butterfly’s apparent absence from flat terrain and the high density of hostplant cover associated with metalmark colonies, it seems unlikely that the total area of suitable habitat in the Similkameen drainage can be much more than 50 hectares.

All metalmark colonies in Saskatchewan are found in badlands habitat within the present or proposed future boundaries of Grasslands National Park (GNP).  There are approximately 300 km2 of badlands habitat in GNP west block (Frenchman River Badlands) and 80 km2 in GNP east block (Rocky Creek or Killdeer Badlands) (Pepper pers. comm.).  Only the east block badlands are close to similar habitat in the United States.  Metalmark colonies were confined to barren slopes of partially weathered shale and clay (Hooper 2002).

 

Figure 5.  Metalmark Habitat – British Columbia.

 Figure 5.  Metalmark Habitat – British Columbia.

 

 

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Figure 6.  Metalmark Habitat – Saskatchewan.

 Trends

It is difficult to assess the changes in habitat available to Mormon Metalmarks in British Columbia.  Both the Okanagan and Similkameen Valleys have been subject to extensive agricultural development and growth of the human population.  The occurrence of dense hostplant sites and metalmark colonies along transportation corridors suggest that some human activities may actually improve habitat availability.  On the other hand, the immediate impact of construction activities could well cause extirpation of existing colonies.  The introduction of Eurasian weeds, such as Bromus tectorum L., Centaurea diffusa Lam. and Linaria dalmatica (L.) Mill., may have reduced the dominance of the buckwheat hostplant and native nectar sources (Cannings et al 1998). 

In Saskatchewan, the badlands habitat available to Mormon Metalmarks has probably been stable, and should remain so for the foreseeable future.

Protection/ownership

None of the presently known sites in British Columbia is protected.  Four are on privately owned land, one is on a roadside on Indian Reserve no. 8 (Skemeoskuakin) and the remainder are on transportation corridor right-of-ways.

In Saskatchewan, three of the six metalmark colonies are within the current boundaries of Grasslands National Park.  The remaining colonies are located on large ranches (Hooper 2002) within the proposed boundaries of the park.