Moles, Shrews Can Smell Prey While Underwater, Study Suggests

John Roach
for National Geographic News
December 20, 2006
Get a whiff of this: Two small, semiaquatic mammals can use their sense of smell even when underwater, according to a new study.

The finding stems from high-speed video that shows a star-nosed mole rapidly blowing out bubbles of air and sucking them back in while foraging underwater.

The bizarre-looking rodent is already known as the world's fastest mammalian forager.

The mole has now displayed equal prowess as a lightning-fast underwater sniffer, blowing and inhaling air bubbles at a rate of five to ten times a second.

The bubbles make contact with a target, such as morsel of earthworm or fish, and apparently pick up the target's scent before being sucked back up the nose.

When you watch the video, "you're essentially seeing [the moles] sniffing underwater," said Kenneth Catania, a biologist at Vanderbilt University in Nashville, Tennessee.

"But that took a little while to dawn on me. You don't see what sniffing looks like in the air—it's invisible," he said. "Underwater it's visible."

Sniff Tests

On land, small mammals sniff by pushing air out and quickly inhaling, Catania said.

The air carries odors to special cells inside the nose that detect smells and send signals to the brain to help interpret the scent.

To determine if the moles were actually using air bubbles to transmit underwater smells, Catania trained the creatures to follow a scent trail that was underneath a submerged wire mesh.

The mesh prevented the moles from using the sensitive, fleshy appendages that ring their noses to feel the trail or the prey.

The moles reached their reward—an earthworm—about 85 percent of the time.

"Discovering a very unusual behavior in an unusual animal raises the question of whether or not some other animals are capable of it," Catania said.

So zoologist Kevin Campbell at the University of Manitoba in Canada provided Catania with water shrews that also blow bubbles while foraging underwater.

Reporting in tomorrow's issue of the journal Nature, Cataina found that during a similar experiment one shrew was accurate in following 80 percent of the trails, while another had 85 percent accuracy.

"In a lot of ways it's more compelling to find a normal-looking animal doing this behavior," Catania said. "It might be a common thing for small mammals to do."

Important Study

Neal Woodman studies shrews and other North and South American mammals with the U.S. Geological Survey Patuxent Wildlife Research Center's office at the Smithsonian Institution in Washington, D.C.

He said the finding makes sense; the small mammals probably use both smell and touch when foraging underwater.

(Related photo: marine iguana foraging underwater.)

Previous researchers must have ignored—or just didn't see—the bubble-blowing behavior.

"What this [study] does is say, Hey look, the sense of smell really is possible here. We should look at it more carefully and consider it. It's an important study," he said.

In future research, Vanderbilt University's Catania hopes to determine how common underwater sniffing really is.

He believes that other small, semiaquatic mammals probably evolved the ability.

But he suspects that air bubbles blown by larger mammals may not hold together well enough to survive the exhale-inhale sniffing action.

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