New Scientist
Betsy Mason
KILLER whales and chimpanzees both pass on “traditions” to other members of their group, according to two separate studies of feeding behaviour. The findings add to evidence that cultural learning is widespread among animals.
One study involved killer whales at Marineland in Niagara Falls in Ontario, Canada. An inventive male devised a brand new way to catch birds, and passed the strategy on to his tank-mates. The 4-year-old orca lures gulls into his tank by spitting regurgitated fish onto the water’s surface. He waits below for a gull to grab the fish, then lunges at it with open jaws. “They are in a way setting a trap,” says animal behaviourist Michael Noonan of Canisius College in Buffalo, New York, who made the discovery, “They catch three or four gulls this way some days.”
Noonan had never seen the behaviour before, despite three years of observations for separate experiments. But a few months after the enterprising male started doing it, Noonan spied the whale’s younger half-brother doing the same thing. Soon the brothers’ mothers were enjoying feathered snacks, as were a 6-month-old calf and an older male. Noonan presented the research this month at the US Animal Behavior Society meeting in Snowbird, Utah.
Wild dolphins off the west coast of Australia were the first marine mammals in which cultural learning was observed. They apparently learn from group-mates how to use sponges to protect their snouts while scavenging (New Scientist, 11 June, p 12). But the evidence from killer whales is much more conclusive because the process was observed from start to finish.
Some researchers have suggested that many purported examples of cultural transmission can instead be explained by individuals discovering the skill on their own rather than following another’s lead. But because the gull-baiting behaviour is so unusual, “it would be hard to argue that it is individual learning”, says ethologist Janet Mann of Georgetown University in Washington DC, one of the authors of the dolphin sponging study. Behavioural scientist Andrew Whiten of the University of St Andrews in the UK agrees, “This is a particularly clear set of observations.”
Whiten and his colleagues have meanwhile shown in a separate study that when chimpanzees learn a skill from their peers, they tend to stick with that method even if it isn’t the most effective. Whiten’s team taught two female chimps how to get food from a complicated feeder using a stick to move a barrier. One chimp learned to lift the barrier while the other was taught an apparently more efficient poking method. The chimps’ group-mates were then allowed to watch their respective experts at work.
The chimps followed the lead of their own expert chimp – the poker’s group preferred to poke and the lifter’s group lifted (Nature, DOI: 10.1038/nature04047).
And even when some lifters learned to poke, the majority reverted to the group’s original lifting strategy.
Getting the message
Chimpanzees appear to be capable of communicating using sounds that refer to specific objects, according to a study of sounds made in response to different foods. It is the first time this ability has been demonstrated in chimps.
Primatologist Katie Slocombe of the University of St Andrews, UK, recorded the grunts made by chimps at nearby Edinburgh Zoo as they collected food at two feeders. One dispensed bread, considered a high-quality treat, and the other doled out apples, a much less sought-after snack.
Slocombe then played back the recordings and watched the reactions of a 6-year-old male named Liberius. The results were striking. After hearing a bread grunt, Liberius spent far more time searching around the bread feeder, while an apple grunt would send him hunting under the apple feeder. Slocombe presented the work at the US Animal Behavior Society meeting in Snowbird, Utah, this month.
This is the first convincing evidence of “referential communication” in chimps, says primatologist Amy Pollick of Emory University in Atlanta, Georgia. Earlier research with a close cousin of the chimpanzee – a male pygmy chimpanzee, or bonobo, named Kanzi – showed that he made specific sounds for four different things: bananas, grapes, juice and yes. But the researchers did not test if the sounds conveyed any meaning to other bonobos, and the same experiments have never been done in chimpanzees.
Liberius, on the other hand, was able to take cues from apple and bread grunts made by at least three different chimpanzees.
Slocombe plans to expand her study to include chimps at the Leipzig Zoo in Germany and hopes to confirm whether the grunts refer to specific foods or to their relative quality.
Betsy Mason