The Unique Voices of Seals
Nowadays, everyone can see seal beaches portrayed on television or in magazines with some frequency. Evidently, producers and editors think there's something innately appealing about rocky coastlines paved with great quantities of lumpy sea mammals sunning themselves and taking care of their various dry-land biological duties. Alaskans who can see seal beaches in the flesh, so to speak, might suggest that the appeal is greater when the deafening, babbling roar of a pack of pinnipeds isn't conveyed along with its picturesque appearance. Seals (and sea lions and walruses, for that matter) shout a lot.
Of course, they have a lot to shout about. Adult males challenge one another for the right to consort with the females; a shouting match may be a preliminary to bloodshed, or may prevent it entirely. (If the other guy's roaring deafens you, it may be wise to turn flippers and hump off along the shore to safety.) There's a certain testy bark-and-yelp exchange useful in defending desirable patches of stones from neighbors' encroaching blubbery edges. Most important, there's the exchange of cries between mothers and pups, necessary identifications in a confusing landscape of seal shapes.
Parents who have fetched a toddler from a preschoolers' picnic know that it's possible to pick out the calls or wails of one's own offspring from a din of similar voices. And any child with an adventurous streak knows there's survival value in being able to identify a parental "Hey!" without looking. Extending that understanding from the human realm to the world of smaller-brained seals isn't too difficult.
It's more of a stretch to appreciate that some seals can recognize family voices after a span of years, but they can. This discovery came as one result of an experiment conducted on the fur seals of Alaska's St. Paul Island (which I read about in-of course-Science News, but the July 27 issue of Nature reported the work in more detail). Stephen Insley, a researcher based at the National Zoological Park in Washington, D.C., knew that northern fur seal mothers left their young pups for as long as two weeks. The mothers needed the time at sea to catch fish and thus replenish their energy reserves so they could produce enough milk to feed the pups. Pups and mothers had to be able to pick out one another from the mob after this separation, which meant they had to have good memories for the sound of a specific voice.
Insley tested this logical assumption by tape recording 26 different seals from a single cove on St. Paul, then replaying the tapes back to different seals. If a seal heard the voice of its pup (or pup its mother), it either moved toward the speaker playing the tape or at least attended to it. The reaction was the same whether the recording had been made a few days or a few weeks before it was played back. The animals did not react that way to the voices of other seals.
That in itself made a nice tidy experiment, validating by observation and test that seal mothers and pups do indeed use voice recognition-but Insley didn't stop there. He tested six mothers and offspring when they returned to the beach the following year; they still recognized their close relatives' voices. Finally, he tested a few young females four years later. Those seals still attended to their mothers' recorded, four-year-old calls.
No one knows what use it is for seals still to hearken to Mamma when they are full grown, but it's fun to speculate. Given the shove-and-push style of a seal beach, for example, it might just help the family gene pool's survival to be able to remember how kinfolk sound when they say "Ouch!"
