SUNY ESF
Pygmy Shrew

(Sorex hoyi Baird)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Order: Insectivora
Family: Soricidae

The pygmy shrew is brown above and gray below, with a darker olive cast to the brown during winter. The brownish-gray tail is slightly darker above and towards the tip. Even astute biologists confuse the pygmy shrew with the abundant masked shrew which it closely resembles, and positive identification in the field is difficult. In hand, the pygmy shrew, which averages 89 mm (3.5 in) in length, has a relatively shorter tail than the masked shrew (about a third of its total length), relatively smaller feet, and a blunter snout. The only reliable means of separating the two is by examining the teeth. Under low magnification, e.g., with a hand lens, the side profile of the pygmy shrew’s upper jaw shows only three large unicuspids instead of five typical of the masked shrew.

Range and Habitat

The pygmy shrew occurs throughout most of the boreal and northern temperate forests of North America, and along a narrow corridor extending southward in the Appalachians into North Carolina. Within these regions, it lives in deciduous, coniferous, and mixed forests, marshes, bogs, and disturbed areas, (for example, clearcuts). Moist forest floors with an accumulation of debris offer optimum habitat, their crumbling logs, trunks, and the soil beneath providing ideal sites for the tiny maze of tunnels that form the burrow system. This species is probably more abundant in the Adirondacks than museum records indicate because of the bias of conventional capture methods which fail to catch this small mammal.

Food and Feeding Behavior

Larval and adult insects, including ants, flies, beetles, caterpillars; and others small invertebrates such as spiders, slugs, snails, and earthworms make up most of the diet. Small quantities of plant materials may be eaten, too. The appetite of a pygmy shrew is enormous, a consequence of the small body mass, rapid heat loss, and high metabolic rate. A pygmy shrew kept in captivity provides some notion of the energy requirements of the species. It consumed parts of the bodies of 20 masked shrews, one white-footed mouse, one red-backed vole, one pygmy shrew, plus 22 grasshoppers, 20 houseflies, 2 crane flies, one beetle, and the liver of a meadow vole, all during the span of 10 days. A single pygmy shrew would need 711 nymphs of the larch sawfly to satisfy its daily energy requirements, which indicates the potential impact of shrews on insect populations.

Activity and Movement

 A few published observations of pygmy shrews kept in cages offer the only reliable information about activity patterns and locomotion. These indicate nearly continuous activity day and night, sudden starts and stops alternating with bouts of searching, feeding, and running, the long flexible nose twitching constantly, the tail extended in an upward curve while running. Captive shrews climb readily, dangling from wire mesh cage covers, leap heights of 11 cm (4.3 in) and sleep in a curled up position. One dug tiny earthworm like holes in the soil in its cage.

Reproduction

The reproductive biology of this species is virtually unknown. The scant information available is from a small number of pregnant or lactating females caught in traps. These suggest a female bears a single litter of  3-8 young, June-August, which if true, is unusual because most soricids bear multiple litters.

Predators

Known predators include the garter snake, and broad-winged hawk.

Social Behavior

• Social system - No information is available. Population densities estimated from trapping studies in Ontario indicate 0.52-1.2 pygmy shrews per ha (0.21-0.5 per acre).
• Communication - Again, little is known about the ways in which pygmy shrews communicate. During the breeding season males emit a strong-smelling, yellowish musk from the typical soricid lateral skin glands which suggest a probable role for scent communication.

Additional References

Long, C.A. 1974. Microsorex hoyi and Microsorex thompsoni. Mammalian Species, 33:1-4.

Malinowski, E.A. 1981. Small mammal survey of Essex County, New York. M.S. Thesis, Shippensburgh State College, PA 168pp.

Prince, L.A. 1940. Notes on the habits of the pygmy shrew, Microsorex hoyi in captivity. Canadian Field Naturalist, 54(7):97 – 100.

Ryan, J.M. 1986. Dietary overlap in sympatric populations of pygmy shrews, Sorex hoyi, and masked shrews, Sorex cinereus, in Michigan. Canadian Field Naturalist, 100(2):225 – 228.

Saunders, P.B. 1929. Microsorex hoyi in captivity. Journal of Mammalogy, 10(1):78 – 79.