For the first four months of its life, an Antarctic fur seal pup depends on its lactating mother for sustenance. The mother seal spends the majority of her time in the ocean on foraging trips, returning to the land every four to seven days to feed her pup for a few days or less.
During the breeding season, Antarctic fur seals can congregate in dense colonies of over a thousand individuals – and, because mother seals will only nurse their own pups and can be aggressive toward pups that are not their own, a pup’s ability to recognize its mother is crucial.
Scientists know that seals in the family Otariidae, or eared seals (so named because they have external ears), including the Antarctic fur seal, use vocal cues to communicate and recognize one another. Mothers and pups may also use sight and smell to find each other, but auditory clues appear to be their most effective means of reunion. A new paper recently published in the journal PLoS ONE elucidates new details of how an Antarctic fur seal pup recognizes the voice of its mother, and some limits to that auditory recognition.
Researchers working on Courbet Peninsula in the Kerguelen Islands in the southern Indian Ocean studied a colony of 750 pairs of mothers and pups. They recorded the calls of mother seals and played them back to the pups, sometimes with modifications to amplitude and frequency, to determine which acoustic aspects of the calls the pups were using to recognize their mothers. The scientists recorded the number of calls the pups made in response to the recordings, as well as how long it took the pups to respond, and how long it took the pups to look at the loudspeaker standing in for the mother seal.
The researchers also noted that the pups often gathered in groups of about 10 individuals while waiting for their mothers to return to land; they took advantage of these gatherings, and played mother seal calls to them from about 25, 100, and 200 feet away to see how well the pups could discriminate mother seal calls at progressively longer distances.
The pups responded best to mother seal calls that were not modified in amplitude or frequency, suggesting that they use both of those signals in recognizing their mothers’ voice. They also appeared to be better at discriminating mother seal calls at shorter distances – when the scientists played the vocalizations of one of their mothers to the groups of about 10 seal pups, about four pups typically responded from 200 feet away, three from 100 feet away, and just one from 25 feet away. The researchers also note that “[f]or all tested distances, the filial pup of the female chosen for the playback always responded.” In other words, while some pups got it wrong, the pup whose mother they were actually listening to always got it right.