'Sponging' Dolphins May Be Sharing Culture
Monday, June 27, 2005
When marine biologists first spotted bottlenose dolphins cavorting off the coast of Australia wearing sea sponges on their snouts, they didn't know what to make of the odd behavior.
Now, an international team of researchers has produced evidence that the animals' antics represent a form of culture, which would add the dolphins to an elite group of species that pass traditions down through generations without being compelled by their genes.
"We define culture as a behavior that is acquired by imitation and passed on in a population," said Michael Krutzen, of the University of Zurich in Switzerland, who led the new research. "We think this behavior is an example of that. It's very exciting."
Krutzen and his colleagues believe the dolphins, which live in Shark Bay off the west coast of Australia, wear the sponges while foraging for small fish, crustaceans and other food along channels in the sea floor to protect themselves against sharp coral and stinging critters such as stonefish. It's a trick that appears to be almost exclusively passed from mothers to daughters.
"They wear them like a glove," Krutzen said. "When they go down to the sea floor to probe for prey, there are lots of noxious animals down there. By using the sponge, it protects them."
Many species use tools to perform tasks. Crows, for example, fashion tools out of leaves and twigs to forage for food. And many animals learn behavior by mimicking their elders -- that's how birds develop their songs.
But those abilities stem from instincts that are inherited through genes. Aside from humans, the only other creatures known to transmit behavior purely by interacting with one another are primates. Unrelated chimps pass on techniques for using sticks to fish ants out of nests; different groups of orangutans display unique eating habits, bedtime rituals and other behaviors that researchers believe are examples of socially transmitted culture.
The bottlenose dolphins would be the first marine mammal shown to exhibit similar behavior, indicating that complex social conduct may be more common than had been thought, Krutzen said.
"The boundaries between humans and animals are becoming less and less clear," Krutzen said. "Thirty years ago, people thought humans and animals were very different from each other. No one thought animals used tools. No one thought they had any kind of culture. Those boundaries have been getting fuzzier and fuzzier. Now here's another example."
The findings prompted mixed reactions, with some scientists praising the work and others questioning how firmly Krutzen's team had made its case.
"This is an exciting addition to the catalogue of what we can be increasingly confident are culturally transmitted forms of tool use in non-human populations," said Andrew Whiten, a professor of evolutionary and developmental psychology at the University of St. Andrews in Scotland.
But Bennett Galef, an animal behaviorist at McMaster University in Canada, said the researchers had not proved that the dolphins use the sponges as tools.