It’s hard enough for human parents to recognize the baby-faced, 18-year-old dropped off at the dorm in August as the square-jawed young man retrieved in December. How do creatures with less cortex cope?
Quite well, thank you, says Stephen Insley of the National Zoological Park in Washington, D.C.—at least if the parent is Callorhinus ursinus, the northern fur seal.
Fur seal mothers are unique among mammals, Insley says, for leaving nursing pups for up to 2 weeks while foraging. When they return, they somehow find their young among the crowd. At 4 months of age, the pups strike out on their own, migrating south for the winter. Parents and offspring tend to meet again at the Alaska site the next year.
For all the time apart, mothers and offspring in a cove on St. Paul Island, Alaska, didn’t forget each other’s voices, Insley reports in the July 27 Nature.
When he played tapes of 26 animals recorded either 2 to 3 days or 3 to 4 weeks earlier, each seal moved toward or attended to the speaker broadcasting the voice of its mother or pup. The length of the interval made no difference. Tapes of familiar but unrelated seals didn’t elicit such behavior.
Insley tested six mothers and offspring that returned the next year. They exhibited similar recognition of the year-old calls. When he tested a few females returning after 4 years, they still attended to speakers playing 4-year-old calls of their mothers.
The study “helps to fill the gap in our knowledge about long-term social relationships,” says Jill Mateo, a Cornell University psychologist. Long-lasting cooperative associations of mammals and prolonged monogamy in birds hint at long-term social memory in those species, she says, but field studies are difficult.
“Insley’s paper is important in providing experimental support for . . . anecdotal observations,” agrees Marc D. Hauser, a Harvard University psychologist. He says similar results might turn up in primates, elephants, and social carnivores such as wolves.
Sociality can actually interfere with measuring social memory, Insley says. “Just because an animal has a stable group for long periods of time doesn’t mean they’d remember each other if removed,” he argues. Animals may recall environmental features rather than individuals.
Ted Miller, a biologist at Memorial University of Newfoundland in St. John’s, says the adaptive significance of recall between 4-year-olds and mothers is unknown. If the phenomenon isn’t merely a byproduct of the seals’ intelligence and long life, he says, it will require a new understanding of the females’ interactions.
Though Hauser and Miller praise Insley’s study, they both say that researchers need to find how much the seals’ calls change over time. If calls retain identifying features, the feats of recognition are less remarkable than if physical changes in offspring radically alter their calls, say the researchers.
A baby-faced juvenile who stays a baby-faced juvenile even after dorm life is, after all, pretty easy to pick out.