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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).
Diet
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.
Habitat
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!).
Reproduction
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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