Townsend's mole (Scapanus townsendii) COSEWIC assessment and status report: chapter 6

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Biology

General

Townsend’s moles are fossorial, adapted for digging tunnels and a life underground. The vestigial eyes of Townsend’s mole can only detect light intensity. It has an acute tactile sense from the vibrissae and its snout. The senses of smell and hearing are probably not well developed. Because of their small size and consequently high metabolic rate, they consume large amounts of soil invertebrates and some plant matter. Townsend’s moles breed in the first year of life and produce an average of 3 young per year during a 3-4 year lifespan. They are solitary and territorial with densities of 0.42-12/ha, depending upon the quality of the habitat. They have few natural predators.

Reproduction

Male Townsend’s moles with enlarged testes are found as early as November (Moore 1939, Pedersen 1963). Females are in breeding condition from early December to late February, at which time embryos are found (Pedersen 1963). Mating in Oregon populations peaks through January into early February (Pedersen 1963). Breeding in Canada is probably later because of the latitudinal gradient.

The young are born and raised in an underground nest during late March or early April. The nest, constructed just before parturition (Pedersen 1963), is built of coarse grass, lined with thin grass, in a chamber about 20-23 cm in diameter and 15 cm high. The nest is 15-20 cm below ground, connected to one of the deeper main tunnels in an elevated part of the territory, presumably to prevent flooding (Kuhn et al. 1966, Pedersen 1966, Caraway et al. 1993). Larger hills 30-45 cm high and 70-130 cm in diameter may identify the nest site, or there may be several smaller hills in a cluster or a single large hill at the base of a fencepost (Pedersen 1963, Kuhn et al. 1963).

The nesting chamber has 3-11 or more lateral entrances and is connected to a main tunnel immediately below the nest chamber to facilitate escape. Nests are sometimes reused for more than one breeding season (Pedersen 1966, Carraway et al. 1993, Nagorsen 1996). Lining the nest with moist grass is thought to be a deliberate effort to generate heat in the nest through fermentation (Kuhn et al. 1966, Pedersen 1966). Disturbed nests are usually abandoned unless there are already young present, in which case the mother will sometimes return (Pedersen 1963, Kuhn et al. 1966).

Moles produce one litter per year of 1-4 young with an average of 2.9. Females have 8 mammae. The gestation period is 4-6 weeks (Yates and Pedersen 1982). Newborns weigh about 5 g and are naked for their first 22 days, after which they develop a plush coat of short fur that is complete by 30 days when pups weigh 60-80 g. The young remain in the nest for 30-36 days, dispersing in May and June. Moles can breed in the winter following their birth (Pederson 1963, van Zyll de Jong 1983).

Survival

Townsend’s moles probably have similar survival rates to coast moles, about three breeding seasons (Sheehan and Galindo-Leal 1996). The mole’s fossorial lifestyle protects it from many predators. Male moles looking for mates and dispersing young may travel above ground at night and may be caught by predators of small mammals. Some young animals are killed on highways. Nursery nests may be trampled by cattle.

Winter flooding in lowland areas can kill many moles. In one report, 62 were killed in a severe January flood in Oregon (Giger 1973).

Physiology

The atmosphere of mole runs is high in carbon dioxide and low in oxygen. Schaefer and Sadleir (1979) determined that for coast moles carbon dioxide reached a maximum tunnel concentration of 5.5%, while the oxygen minimum was 14.3%. The rarified atmosphere is particularly problematic given that moles are working hard underground, sometimes moving up to 20 times their body weight in 15 minutes (Schaefer 1978).

The European mole is known to have adapted its circulatory system to its environment. The serological composition of the blood is also adaptive with increased hemoglobin, similar to that of humans acclimatized to high altitudes (Dabrowski and Skoczen 1962, Quillam et al. 1971). Townsend’s mole likely has similar adaptations.

Movements/dispersal

Townsend’s moles are territorial. They restrict their movements to a distance of approximately 38 m in length in suitable habitat and 116 m in poorer habitats, with a shorter width. A cluster of hills with a gap before the next cluster clearly defines a territory (Sheehan and Galindo-Leal 1996). Coast moles may move from open agricultural fields occupied in the summer to sodded grasslands in October (Glendenning 1959).

Longer distances (13-856 m) are traveled above ground by dispersing young in late spring and summer, the dispersal distance appears dependent on habitat quality rather than population density (Giger 1973). Townsend’s moles are good swimmers and can cross small water-filled ditches and streams (Moore 1939, Giger 1973).

Dispersal of young occurs through communal tunnels and above ground. Many juveniles are killed on roads and are eaten by owls (Pedersen 1963, Campbell 1983).

Moles displaced 100-200 m by natural flooding reoccupy their original territories when the water subsides. Those relocated artificially for distances up to 450 m also return to their territories (Giger 1973).

The habitat of Townsend’s mole in Canada is continuous with a small area of habitat in the United States.

Nutrition and interspecific interactions

Townsend’s mole primarily eats soil invertebrates. Most of its diet (average 76%, range 55-86%) consists of earthworms (Wight 1928, Whitaker et al. 1979). Another 8% of the diet consists of insects and their larvae and other invertebrates such as centipedes, millipedes, slugs and snails. Shrews and mice have also been found in stomach contents. The remaining 16-38% consists of vegetable matter – bulbs, vegetables and grass roots (Wight 1928, Moore 1933, Pedersen 1963, Whitaker et al. 1979). The latter distinguishes it from the Pacific coast mole, which consumes exclusively animal matter. It also makes Townsend’s mole a pest in agricultural and residential areas because it eats bulbs and roots and can cause considerable damage to tulips, iris, potatoes and carrots. Townsend’s mole does not require free water due to the high moisture content of its diet.

Mole tunnels operate as an elaborate pit trap system in which moles forage for invertebrates. Larger earthworms such as Lumbricus terrestris of the Family Lumbricidae that form a major part of Townsend’s mole’s diet were introduced from Europe to the Pacific Northwest abut 200 years ago. Moles likely ate more insect larvae in the past (Schaefer 1984). The dentition is similar to that of shrews that eat more insect larvae with tough chitinous exoskeletons.In a single day, Townsend’s mole regularly consumes 33-66% of its body mass in food (Cahalane 1947, from Carraway et al. 1993), and it has been known to eat 1.4 times its body mass in one day (Nagorsen 1996).

Predation on Townsend’s mole is minimal and mainly on dispersing young (van Zyll de Jong 1983). They are sometimes caught by weasels (Mustela spp.), rubber boa (Charina bottae) (released pets), Great Horned Owl (Bubo virginianus), Barn Owl (Tyto alba), Red-tailed Hawk (Buteo jamaicensis) and coyote (Canis latrans), and pets such as dogs and cats. Cows may be attracted to the nests by the smell of the fresh grass used as a lining, and may trample young in underground nests (Pedersen 1963).

The tunnels of Townsend’s mole are often communal and are used by mice and voles that may carry Hantavirus. This has been identified as a concern when handling moles (BC Ministry of Environment, Lands and Parks 2001).

Behaviour/adaptability

Townsend’s mole tunnels are of four basic types (Pedersen 1963), including a permanent system 10-20 cm deep used to move around the territory and more abundant shallower tunnels 1-10 cm deep used for feeding. Most earthworms occur in the top 7.5 cm of soil for most of the year (Edwards and Lofty 1972). Occasionally Townsend’s moles will construct tunnels up to 3 m deep to pass under roadways and other obstructions, or to find earthworms during hot, dry periods. During the breeding season and dispersal, moles may dig temporary tunnels just below the surface while looking for mates.

The mole digs with its front paws. The excavated material is pushed to the surface where it forms hills on the surface above the subterranean runways. The size of molehills vary. Small hills may indicate repair to existing tunnels whereas larger hills are indicative of new tunnels. An average size for hills of Townsend’s mole is 17 cm high and 43 cm in diameter with the diameter of the vertical tunnel shaft being 5 cm. The digging behaviour of Townsend’s mole can be distinguished from that of the coast mole by greater mole mound heights, widths, tunnel diameters and volumes for Townsend’s mole (Sheehan and Galindo-Leal 1996).

The density of Townsend’s moles in British Columbia is unknown. In Oregon there may be 12/ha in good habitat and 0.4/ha in poor habitat. There may be as many as 805 molehills/ha in good habitat at some times of the year (Yates and Pedersen 1982).

Although information about daily activity is not available, it is probably similar to that of the coast mole that has an 8 hour rhythm characterized by 4 hours of activity followed by 4 hours of sleep (Schaefer 1982). Various researchers report observing the Townsend’s mole to be active throughout a 24-hour period (Pederesen 1963, Giger 1973, Sheehan and Galindo-Leal 1996).