Whether it's learning a new song, figuring out how to use tools to forage for food, or picking up the local customs, learning from others is an important part of life for many animals, including people.
The idea of a culture or traditions—behavior shared by an identifiable group and acquired through social learning—in cetaceans, a group including whales and dolphins, has been controversial.
But a new study finds strong evidence that a group of humpback whales (Megaptera novaeangliae) in the Gulf of Maine (map) is sharing a newly observed feeding behavior via their social networks. (See related blog: "Sharks Have Social Networks, Learn From Friends.")
That behavior, called lobtail feeding, was first recorded in one whale in the Gulf of Maine in 1980. Since then, 278 humpback whales—out of about 700 observed individuals that frequent the Stellwagen Bank (map) area—have employed the strategy, according to the study, published this week in the journal Science.
"I've been arguing for over a decade now that cultural transmission is important in cetacean societies," said study co-author Luke Rendell, a marine biologist at the University of St. Andrews in Scotland.
Though he wasn't surprised the whales traded information, he was surprised at how strongly his data said the whales learned the new feeding strategy socially, rather than because of other factors like having a genetic predisposition to the behavior.
Lobtail feeding is a variation on a technique called bubble-net feeding, which is used by humpbacks around the world.
In bubble-net feeding, a whale blows bubbles into a kind of net surrounding the prey, corralling them into dense schools. Then the whale lunges up through the school with its jaws wide open, scooping up mouthfuls of food. (Watch a video that shows humpbacks bubble-net feeding.)
In lobtail feeding, the humpback slaps the surface of the water one to four times with the underside of its tail before diving down and blowing the bubble net. Rendell speculates the slaps may keep its sand lance prey from jumping out of the water, away from the whale.
"The origin of this behavior was strongly associated with the collapse of herring stocks and a boom in sand lance stock," said Rendell. So he and his team suggest that lobtail feeding came about when humpbacks switched from hunting herring to catching sand lances, a type of fish.
To track the spread of lobtail feeding in the whale population, the researchers combined data on fisheries stocks with a sampling of a long-term dataset (1980-2007) on humpback whale observations. The data are compiled by trained observers from the Whale Center of New England.
Not only did the use of lobtail feeding increase with corresponding peaks in sand lance populations in the '80s, Rendell and his colleagues found that knowledge of the new feeding behavior mirrored the loose social connections among the whales.
Basically, a naive whale—an individual who didn't exhibit lobtailing behavior—was more likely to start lobtailing if it associated with a whale that did use the new technique.
The new study is a good proof of concept showing scientists can use this kind of network analysis in looking at questions of traditions and social learning, said Bennett Galef, a retired professor at McMaster University in Ontario, Canada, who specializes in social learning.
But Galef, who was not involved in the study, cautioned that a behavior can spread through a population without social learning.
It could be that since these animals move around together, they just pick up the same behavior at the same time, said Galef. "That's not culture."
Experiments can home in on how information spreads throughout a population better than observational studies can, he added. But Galef acknowledges that you can't exactly bring whales into a laboratory.
Simon Reader, a behavioral biologist at McGill University in Quebec, Canada, agreed that observational studies can be problematic. For instance, it's possible there's an alternate explanation for the spread of lobtail feeding in these humpback whales, he said.
"But I think there's pretty strong evidence for social learning."