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Scientific name: Blarina brevicauda
Common name: 
Short-tail Shrew

Information in this Species Page was compiled by Aaron Serene in Biology 220W, Spring 2000, at Penn State New Kensington.

The Northern Short-tail shrew is a small, dark gray, "mouse-like" animal that is found abundantly throughout the Nature Trail. Shrews are members of the Order Insectivora of the class Mammalia. Insectivores are an extremely ancient groups of mammals. Fossils of insectivores dating back 130 million years have been described. Shrews and the ancestors were probably the prey of many types of small and medium sized dinosaurs!

Appearance and Venom
Adult short-tail shrews are four to five inches long and weigh 0.4 to 1.0 ounces. They have a stocky build and short, dense, slate-gray fur. Their long, pointed noses and small eyes and ears distinguish them from mice. Short-tail shrews also have a mouthful of 32 sharp teeth and are among the very small number of mammalian species that have venom glands. Shrew venom is a neurotoxin that is powerful enough to immobilize or even kill small prey species like frogs and mice. The venom can cause swelling and irritation in larger organisms (like humans).

Shrews are opportunistic predators taking whatever prey season, habitat or opportunity presents. Prey includes mice, moles, salamanders, frogs, birds, bird eggs, all types of insects, slugs, snails, isopods, spiders, millipedes and centipedes. Shrews will also eat roots, berries, nuts, fruits, fungi and general vegetable materials if prey is limited or if these materials are abundant. Shrews must continuously eat in order to sustain their very high rate of metabolism. They are active all year round (they do not hibernate) and rely on cached food materials for consumption during times of resource limitations. A short-tail shrew must eat every two or three hours or they will succumb to starvation.

Short-tail shrews forage very actively in soil and leaf litter and even down into the burrows of other, larger animals. Their thick, stocky bodies are well adapted to pushing through dense leaf litter and vegetative debris. Shrews rely on their excellent senses of smell, touch and hearing to locate food. Their noses are richly innervated with olfactory receptors, and their snouts have dense groups of vibrissae (whiskers) to aid in tactile sensation. There is some speculation that shrews may use very high frequency vocalizations and their subsequent rebounding off objects to echolocate position and prey.

Short-tail shrews are found in a great variety of habitats but are especially abundant in moist environments with dense vegetation and thick layers of leaf litter. In the winter, the short-tails dig shallow tunnels through the snow and also rely on the subnivian space for both shelter and for foraging. Short-tails have a foraging range of 0.5 to 1.0 acres which can shift and fluctuate from season to season.

Shrews communicate primarily via scent markings and vocalizations. Two prominent sets of scent glands located on their bellies and on their flanks produce an array of pungent secretions that are used to mark individuals, territories and cache locations. Scent is also quite important for males to locate females during the breeding season which runs from March to September (but may begin even as early as January!).

After mating, the female builds a 12 to 15 cm diameter nest out of plant debris and hair. Nests are typically located under logs, stumps, rocks or other debris. Gestation is 21 days and results in the birth of 5 to 7 young. The young shrews start out the size of a honeybee but by 25 days are nearly fully grown, weaned, and are able to leave the nest and live on their own. By three months of age the shrews are able to reproduce. In a single season, then, two or even three generations of short-tail shrews can be born. This compression of generation times enables shrew populations to potentially increase at very rapid rates. Few of the shrews born in a given generation, though, survive even the three months needed to reach maturity. Predation pressures by hawks, owls, snakes, opossums, raccoons, foxes, weasels, and housecats can be quite heavy. Many predators, though, learn to avoid shrews (or only eat them in times of extreme need) because of the offensive smells produced by their very potent scent glands.

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