Townsend's mole (Scapanus townsendii) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

Based on the information available, 28 specimens collected since 1927 (Table 1) and locations of 16 territories located to produce this status update, the population appears stable in the Huntingdon area. It may even have expanded slightly toward Abbotsford. The latter population was discovered only after intensive trapping, and moles may have been there undetected until 1995. Townsend’s moles were caught in fall 2001 at the Ledgeview Golf Course and Marshall Road sites east of Abbotsford (Sheehan pers. comm.) and hills were found at these sites in May 2002 during the current study. Intensive trapping further east may reveal a wider Canadian range.

Townsend’s mole is less common than the coast mole that shares its range in Canada. Of 25 individuals collected during 1,308 trap-nights at 22 sites, 3 were Townsend’s moles and 22 were coast moles (Sheehan and Galindo-Leal 1996). That study used live traps, that often jam or are avoided, so the number of moles caught is not a reliable estimate of population size.

Estimates of Townsend’s mole densities in other areas range from 0.42-12/ha (Pedersen 1963, Kuhn et al. 1966, Giger 1973). As Townsend’s mole is at the northern edge of its range, the lower density estimate of 0.42/ha (or 42/km²) is more realistic (Nagorsen 1996). Sheehan and Galindo-Leal (1996) report a crude estimate of 700 adults in Canada. This is based on a suitable amount of habitat of 13 km² within Townsend’s mole’s range around Huntingdon-Abbotsford and a density of 0.5 moles/ha for a total of 650 that they rounded up to 700. The current study confirmed that the density remains low and found no reason to revise this estimate.  Mature adults may represent about 60-70% of the total population, so 420-490 adult Townsend’s mole may occur in Canada.  With an average of 3 young born per female and a 1:1 ratio of males to females, we would expect 3/5 of the population to be young. However, the proportion of juveniles is likely lower because not all adults reproduce, juvenile mortality is high during dispersal and adults survive an average of 2-3 years.

Reliable estimates of population size are difficult because of the fossorial nature of moles. Townsend’s moles may be more abundant in pastures fertilized with solid cow manure, which improves conditions for earthworms (Pedersen 1963).

Field work conducted on November 18, 2001, and January 3, 2002, relied on molehill sizes and tunnel diameters to distinguish Townsend’s mole territories from those of the coast mole, which are smaller (hill size of 30 x 11 cm and tunnel diameter of 3.6 cm). These characteristics are reliable according to Sheehan and Galiano-Leal (1997), and recommended by the Resources Inventory Committee (BC Ministry of Environment, Lands and Parks 2001).

Of 18 mole territories in Huntingdon between the International Boundary, Riverside Road, Vye Road and Angus Road, three appeared to be those of Townsend’s moles, a ratio of 6:1 coast moles to Townsend’s moles that is consistent with the live trap results obtained from the earlier live trap study. There were 16 Townsend’s mole territories located from roadside searches during the present study. This appears to represent a slight expansion of the range from that reported by Sheehan and Galindo-Leal (1996). There were 137 coast mole territories found in the same area and outside the perimeter of the range of the Townsend’s mole in the current study. In 1995 Townsend’s moles were caught with live traps on Marshall Road and at Ledgeview Golf Course (Sheehan and Galindo-Leal 1996), and were caught with scissor traps in the same area in fall 2001 (Sheehan pers. com.). They appear to be excluded from the urbanized centre of Abbotsford.

About 30 km² of silt loam soil exists in the Fraser Valley, some around Mission where no Townsend’s moles have been found. The Huntingdon/Abbotsford area potentially has about 20 km²  of this habitat, although some has been developed for housing and roads. Sheehan and Galindo-Leal (1996) estimate that the Townsend’s mole is found in an area of 13 km². Additional contiguous suitable habitat occurs south in a band of lowlands associated with Johnson Creek and the Sumas and Nooksack Rivers in Washington State (Appendix D). This lowland area is about 4 km wide and extends from the border southwest 9 km to Nooksack (representing 36 km² of available habitat) and beyond. A search in May 2002 found no hills of Townsend’s moles in the city of Sumas. Three territories were located in a pasture along Highway 546 southwest of Huntingdon. However, hill construction is most active during winter.

Townsend’s moles may be prevented from access to the habitat north and east around Mission by the City of Abbotsford and the Fraser River, which lie between Mission and Huntingdon. The silt loam soil extends into Washington State.

Coast moles will very quickly re-invade cleared areas. It took 9 successive years of trapping a 60 ha field before the numbers of coast moles dropped appreciably (Glendenning 1969). However, a field cleared of Townsend’s moles was re-invaded by coast moles and Townsend’s moles failed to re-establish themselves (Pedersen 1963).