Plugged In : Without whiskers, an electric sensibility : Newborn bottlenose dolphins sport hairs along the tops of their jaws. But once the animals are weaned, the whiskers fall out.

'' Everybody thought that these structures are vestigial - so without any functions,'' said Guido Dehnhardt, a marine mammal zoologist at the University of Rostock in Germany.

But Dr. Dehnhardt and his colleagues reported in The Journal of Experimental Biology that the pits left by those hairs can perceive electricity with enough sensitivity that they may help the dolphins catch fish or navigate.

Dr. Dehnhardt first studied the whisker pits off a different species, the Guiana dolphin. He expected to find the typical structures of hair follicles, but those were missing.

Yet the pits were loaded with nerve endings. He and his colleague realized that the hairless follicles looked like the electricity - sensing structures on sharks and found that one Guiana dolphin responded to electrical signals. They wondered whether other toothed cetaceans, including bottlenose dolphins, could also sense electricity.

The researchers trained two bootlenose dolphins to rest their jaws, or rostrums, on a platform and swim away anytime they experienced a sensory cue like a sound or a flash of light, if they didn't detect one of these signals, the dolphins were to stay put.

Once trained, the dolphins also received electrical signals. '' The dolphins responded correctly on the first trial,'' said Tim Huttner, a biologist at the Nuremberg Zoo in Germany and a co-author of the study.

Sharks are far more sensitive to electric fields. But dolphins electrosense might also aid the animals in catching fish while they're hunting. The dolphins spot prey with their eyes and by sending clicking sounds that bounce off prey, known as echolocation.

But fish bodies also produce electrical fields through the activity of their muscles and gills.

Such a signal could also help the dolphins home in on prey hiding on the seafloor. Bootlenose dolphins perform what's called crater feeding, said Dense Herzing, a marine mammalogist at the Wild Dolphin Project in Florida who wasn't involved with the study.

'' They dig,'' she said. ''They put their beaks down into the sand, almost up to the eyeballs, and pullout these eels.'' [ Carolyn Wilke ].


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