Charrier spent nine months on Amsterdam Island in the Indian Ocean, studying and recording acoustic recognition between the female and her pups. When these fur seals come ashore to breed in dense colonies, the lactating females must leave their newborn pups on land while they forage for food at sea. As with most social species, the fur pups only feed their own offspring so when the mother returns from sea, it is essential for the mother and pup to find each other among the several hundred other mammals.
"We found out that pups can recognize their mother's call within two to five days after birth," said Charrier. "This is surprisingly quick but considering that the mother leaves seven days after giving birth it is important to have that immediate recognition."
During her time on Amsterdam Island, Charrier recorded the signals and then modified them to determine which parts of the acoustic parameters support the recognition process. When a mother returns from a foraging trip, she is confronted with both acoustic jamming and a high risk of visual confusion and finding her pup under such conditions should be difficult. Yet Charrier learned that upon return, mothers and pups can recognize each other with seven minutes of the initial call.
If a mother was gone a particularly long time--they can be away for up to three weeks--the pup would become so hungry, it would try to respond to another female's call in an attempt to be fed. But mothers are quick to dismiss and even become aggressive to pups other than their own.
Charrier's work on this experiment has also been published in Nature. It is one of the few studies to investigate voice recognition in mammals. "The only other studies have been done on sheep but the constraint is not the same since mother and baby are always together," she said. "With fur pups, that recognition is vital since separation occurs immediately and frequently."
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