For seal pups, the ability to recognize mom's voice in a crowd can be a matter of life or death: as in most species of colony-dwelling mammals, female seals feed only their own young. Now scientists studying the subantarctic fur seal have found that to facilitate this learning process, the mother delays its first postbirth fishing trip until its call is etched in its pup's memory. The new findings appear in the current issue of the journal Nature.

French biologist Isabelle Charrier of Jean Monnet University in Saint-Etienne and her colleagues used recordings of female fur seal calls to track the development of the pups' responses to their own mother's calls and to those of strangers. They observed that pups react to any female's call a few hours after birth. After two to five days, however, they answer only their mother. The team further notes that the mother's first departure, which occurs two to 10 days after she gives birth, depends on its pup's ability to recognize mom's voice.

When the mother returns from its foraging trip, which lasts between two and three weeks, it begins calling shortly after arriving ashore. Its pup calls in reply, and the two continue the exchange until they are reunited amid the other members of the colony. The system seems to work pretty well. When the researchers measured the time taken by pups to locate their mother on return from the first sea excursion, they found that 66 percent of the mother-pup pairs met up within seven minutes; the others found each other within 11 minutes.