Dusky dune moth (Copablepharon longipenne) COSEWIC assessment and status report: chapter 9

Population Sizes and Trends

Search Effort

Multiple light traps (bucket traps with 12 V UV lights) were set in ten sites in active or semi-stable dunes, sandy habitats, or dry grasslands in southern Saskatchewan and Alberta between July 31–August 6, 2004 and July 23–27, 2005. Copablepharon longipenne was captured in ten of 28 traps from a total of four sites: Dundurn DND Base south of Saskatoon, SK; Seward (Webb) Sand Hills near Swift Current, SK; Cramersburg Sand Hills, SK; and Great Sand Hills, SK. Three of the four sites represent new localities for C. longipenne. A summary of the 2004–2005 trapping results and site information is presented in Appendices 2. Figure 3 also shows the location of known populations, unsuccessful trap sites, and suspected populations. Copablepharon longipenne was not captured at six other sites with dry, sandy grassland or semi-stable or stable sand dunes.

Additional observations of C. longipenne were also made through visual observations and hand-net captures in the Seward Sand Hills on August 5, 2004 and in the Great Sand Hills on July 24 and 25, 2005.

Two points increase confidence in our understanding of the distribution, abundance and habitat requirements of C. longipenne in Canada. First, C. longipenne, where it occurs, is often abundant and easily trapped or observed. Light-trapping is considered very effective in capturing this species and it can also be observed in dune areas at dusk. Second, sampling in 2004 and 2005 provided new information on habitat requirements. Trapping was generally undertaken with multiple traps which allowed sampling over a range of habitat conditions (e.g., active and stabilized dunes). Copablepharon longipenne was only captured in, or adjacent to (<100 m), active sand dunes, and it was abundant only along the sparsely vegetated margins of active dunes.

Copablepharon longipenne has been collected in Alberta only once in the last 50 years, in spite of recent collecting in dune habitats in the province. Chris Schmidt took specimens in a small area of active dune blowouts north of Bindloss in 2007 (Appendix 1). It has not been found in its historical localities in the province.


Abundance

A total of 409 C. longipenne moths were captured ranging from 1–142 per trap (mean of 41 per trap). These captures ranged from approximately 5–65% of the total number of moths captured in these sites, and indicate that C. longipenne can be locally abundant. However, because of uncertainties in measuring capture success, available habitat, and other factors, a population estimate cannot be calculated for C. longipenne. Light-trap captures provide a biased estimate of population size and should be used cautiously for characterizing population density within or between sample sites.

Estimates of larval density, which could have provided an estimate of overall density, were not obtained. Larvae were absent in July and August when light-trapping was undertaken.


Fluctuations and Trends

There is no quantitative information on population fluctuations and trends for C. longipenne. It is difficult to assess with any degree of certainty the population size, variability, and trends in rare nocturnal insects.

Based on the stabilization trends of active sand dunes in the southern Canadian prairies (Wolfe, 2001; Hugenholtz and Wolfe, 2005), it is inferred that C. longipenne populations are declining at a rate of 10–20% per decade. This rate of decline is expected to continue over the next 20 years. These numbers assume that no other impacts are influencing the populations of this species and so these estimates are likely underestimates.

In addition to the recent collecting done in Saskatchewan and Alberta by Page (Appendix 2), Alberta dune areas that have been collected using MV lights and ultraviolet light traps in recent years without encountering longipenne include the Edgerton – Chavin area dunes (collected extensively and repeatedly), the Wainwright Ecological Dunes (once), and the Pakowki Lake dunes, where the species was recorded in 1925 (several times). It is noteworthy that in the Burstall and Great Sand Hills dunes in adjacent Saskatchewan, longipenne was collected in large numbers when found (J. Troubridge, pers. comm. to G. Anweiler).


Rescue Effect

The US population near Fort Peck, Montana is approximately 270 km south of the closest Canadian population. The possibility of rescue over this distance is unlikely. To determine if other nearby populations exist, additional sampling is needed in northern Montana.

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