Wildlife Notebook: Meet Alaska's efficient little carnivores

Shrews are found throughout the state with the exception of the Aleutian Island chain

Posted: Sunday, April 11, 2004

Wolves are Alaska's most famous carnivores, but Alaska has plenty of meat eaters that hunt on the microcosmic level. Close to the ground, amid the litter of the forest floor and at the edges of ponds and streams, mouse-like predators hunt and scavenge. They're shrews.

Shrews are often mistaken for mice, but they're very different animals. They aren't even rodents. They're insectivores, a completely different group. One close look at a mouse and a shrew and the differences are apparent.

Shrews have long pointy noses, long whiskers and short legs. Their ears tend to be small and their eyes are tiny, compared to mice - shrews depend most on their acute sense of smell. Shrews lack the big front incisor teeth so prominent in rodents, and have small, sharp teeth. Most shrews are grayish-brown with a paler belly, and some are distinctly two-toned.

Unlike mice, shrews are loners. In fact, if two shrews are trapped together, one will kill and eat the other. Shrews may occasionally get inside a house, but these aggressive little predators are unsociable insectivores, not colonial rodents, and so they are unlikely to live and breed indoors as mice will do.

Alaska is home to 10 species of shrew, including the tiny pygmy shrew, which weighs less than a dime. The pygmy shrew was considered to be the smallest mammal in the world until the discovery in the mid-1970s of an even tinier mammal, the bumblebee bat of Thailand.

With the exception of the Aleutian Islands, shrews are found throughout Alaska, in all kinds of habitat. Some are excellent swimmers and favor aquatic environs. Two species, the St. Lawrence Island Shrew and the Pribilof shrew, are found nowhere else in the world. The masked shrew and the dusky shrew are the most widespread shrews in Alaska and are found from the Brooks Range to Southeast.

The tundra shrew and the barrenground shrew of Alaska's North Slope are closely related to Asian shrews, a reminder that just a few thousand years ago, when the shallow Bering Sea was a vast expanse of dry land, Alaska and Siberia were part of the same land mass.

Part of the reason shrews are so widespread is because they are such efficient little carnivores. Shrews eat insects, spiders, worms and mice - pretty much anything they can kill, as well as any meat they can scavenge. Aquatic shrews eat small fish, snails and invertebrates.

A few species of shrews have poisonous saliva, (they are the only mammals with a poisonous bite), which is effective at immobilizing worms, bugs and even mice. But the neurotoxin poses little threat to people because shrews are so small, with such a tiny bite that the "injection system" is not very effective.

Shrews will practice surplus killing and will stockpile food when it is abundant. These aggressive little carnivores have an extremely rapid metabolism, and the masked shrew, which is found throughout North America, has a heart rate of 1,200 beats per minute, comparably high respiration, and will eat 75 percent to 100 percent of its own body weight in food every day.

People sometimes find shrews that appear to have been killed by predators and abandoned. There's a reason for this. Shrews have musk glands and give off a strong smell, especially when handled. Because of their odor, and possibly their taste, weasels, cats and other predators will leave them. But plenty of raptors and predators do feed on these tiny carnivores, and like mice, they are a staple of the food chain.

Even without predation, shrews have short life spans, just 12 to 18 months. A female shrew may have two or even three litters over the course of the spring and summer, with two to 10 babies per litter. A baby shrew matures quickly, reaching adult size in just about one month and sexual maturity in just a couple months.

Individual shrews don't live very long, but shrews as a group are very successful. About 300 species of shrews are found throughout the world, with the exception of Australia, Antarctica and South America south of the equator. The earliest ancestors of mammals were shrew-like insectivores.

• Riley Woodford works for the Division of Wildlife Conservation at the Alaska Department of Fish and Game. For comments or questions, he can be reached at riley_woodford@fishgame.state.ak.us. For more about Alaska's wildlife, see www.wildlifenews.alaska.gov

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