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Shrews

07/15/08 5:55PM By Ruth Page
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(HOST) Commentator Ruth Page has lived in Vermont and followed environmental issues for many years. But her fascination for the natural world is as strong as ever, and it still often takes her by surprise.

(PAGE) I’ve been moving into a new apartment, and, after hauling boxes for a couple of hours, I flopped into the nearest chair. Picking up a recent issue of Natural History magazine, I found myself unaccountably drawn to an article about a tiny mammal I knew little about - the shrew. I learned that despite shrews’ penchant for racing about, their little hearts beating fast, their clawed feet racing over the ground, they’re not related to the mice they somewhat resemble. They’re related to moles; also to hedgehogs, of all things. And there’s more than one kind. But I’ve never seen a water shrew, or if I did I didn’t pay attention.

Biologists at the University of Manitoba studied the little shrews and learned some pretty astonishing things. Water shrews weigh only about half an ounce, but in their mini-world they are tough predators. They can shoot straight down into a deep pool in a moving stream, then swim across the water and hide out in the plants growing there. They have iron in their teeth, which may strengthen the enamel, since their teeth don’t keep growing as rodent teeth do.

Like us, they enjoy both land and water, nesting in dry areas but going to the water for their food.

They do their under-water hunting at night, when the water is so dark they can’t see. They can smell, though, even though odors are carried to mammalian noses by air. That’s ok with the swimming shrews: they simply evolved a way to sniff for food under water. They exhale air bubbles through their nostrils, then inhale the same bubbles so they can smell them. It’s quite a trick, though star-nosed moles, also semi-aquatic, do the same thing.

The little swimmers can also use the delicate sense of touch provided by the whiskers around their nostrils; that’s how they work out the shape and texture of what they find underwater.

They’re so fast underwater that when the water moves, they can turn toward the action in a fiftieth of a second. That’s tough on the fish the shrew may be seeking. If the fish hovers in the water, the shrew will be able to smell and touch it; if the fish swims away, the shrew feels the motion of the water and pounces. A fish with lots of room to maneuver may escape, but if it’s in an area of stones and plants, the shrew is likely to win.

It’s not hard to understand why the writer of this article calls shrews the "great white sharks" of their mini-domains.
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