Male harbour seal pups may learn the complex vocalisations they use to woo females years beforehand.
Social mammals like humans and naked mole rats learn calls and sounds from close contact with other members of their species. Harbour seals (Phoca vitulina) spend their lives alone apart from a few weeks of puppyhood. 鈥淭hey are raised solely by their mothers for a couple of weeks, and then they get nourished and swim off,鈥� says at the Max Planck Institute for Psycholinguistics in the Netherlands.
Female harbour seals never use vocalisations. The males, when a few years old and mature enough to breed, perform complex vocalisations for female affection. Earlier work has suggested that these calls are not innate but learned from others, and herein lies the mystery: if male harbour seals spend most of their time alone, how do they learn such complex calls?
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To investigate, D眉ngen and her colleagues combed existing research on harbour seal vocalisations. This included a case study of Hoover, an orphaned pup that was raised by humans during his first few weeks of life.
After a few months old, Hoover outgrew his caretakers and ended up at the New England Aquarium in Massachusetts, where he was silent for years before stunning animal care staff by imitating human speech. Hoover couldn鈥檛 learn new sounds, but he imitated phrases he heard as a young pup, like his own name, 鈥淗ello, there!鈥� and 鈥淐ome over here!鈥�.
The researchers also looked at the timing of seal births and male singing. They found that mothers give birth before males start singing, and the peak singing activity of males coincides with the pup鈥檚 first forages at sea.
This evidence led the researchers to hypothesise that harbour seal pups have a sensitive phase, around 3 to 7 weeks old, during which they learn from males of their own species. D眉ngen says it may work similarly to songbirds, some of which have a sensitive window of auditory learning that ends by adulthood.
However, at the University of California, Santa Cruz, says the idea is ahead of the evidence. 鈥淏efore jumping to a hypothesis about how vocal learning occurs in a semi-solitary animal, I would suggest simply proposing concrete steps to unequivocally demonstrate that harbour seals are, in fact, vocal learners.鈥� Vocal learning in seals has only been hinted at but not proven, so the work 鈥減uts the cart before the horse鈥�, she says.
Ethology
