Dolphins use 'tools' to help hunt for food
In the deep, clear channels of Australia's Shark Bay, bottlenose dolphins have discovered tools, raising questions about the origins of intelligent behavior, the nature of learning. and the birth of technology. There, dolphins in one extended family routinely use sponges, to protect their noses as they forage for fish hidden in the abrasive seafloor sand, according to Georgetown University scientists.
As far as the researchers can tell, a single dolphin may have invented the technique relatively recently and taught it to her offspring. The simple innovation dramatically changed their behavior, hunting habits and social life, the researchers found. Those who adopted it became loners who spend much more time hunting than others, and dive more deeply in search of prey. The sponging dolphins teach the technique to all their young, but only the females seem to grasp the idea. 'It is indisputably tool use,' says primate anthropologist Craig Stanford at the University of Southern California, an authority on animal cognition and behavior. For those seeking a glimpse of our own beginnings, the dolphins of Shark Bay offer a hint of the inventive impulse that occurred when our earliest ancestors first shaped destiny by fashioning implements with their hands.
Tool use of any sort among wild animals is rare, difficult to document reliably, and controversial. The line between instinct, Ingenuity and intelligence is easily blurred by wishful thinking, experts caution. Field observations often give rise to scholarly disputes. Even so, IO primate species of monkeys and apes, along with 30 species of birds, are thought to use sticks, rocks or leaves as tools.
In the first in-depth analysis of this natural dolphin behavior, marine biologist and psychologist Dr Janet Mann at Georgetown University and her colleagues found that the dolphins of Shark Bay use their makeshift hunting masks more often than any other species uses tools, except human beings.
The curious hunting habit was first observed by a local fisherman who reported to marine biologists that he had seen a dolphin with an odd growth on its nose. Monitoring its movements the bay's unusually clear waters, researchers soon discovered that the dolphin was actually balancing a conical basket sponge on its nose.
At first, it was not evident what the dolphin was doing with a sponge. Observing from a small boat, Dr. Mann and her colleagues eventually identified 41 dolphins who regularly used sponges to hunt, cataloging 1,295 dives in which they surfaced with sponges on their snouts. Researchers were startled to realize that the dolphins of Shark Bay employed once living creature as a tool to help hunt another.
Not any basket sponge would do, the researchers soon learned. The dolphins might search for 10 minutes to locate one with the right conical shape to cap their nose, tear it free of its mooring, and then carry it to a preferred hunting ground along channels between eight meters and 13 meters deep. "You can see that they are scattering the sand gently as they go along," says Dr. Mann. 'When they startle a fish out of the sand they immediately drop the sponge and go after it.
'They return to retrieve the sponge and pick up the hunt again, repeating the pattern. "They really use these sponges as a foraging tool," says dolphin biologist Maddalena Bearzi, president of the Ocean Conservation Society of Los Angeles, 'They discovered it could create an advantage in their foraging technique, and they pass it from generation to generation.' However, among the hundreds of dolphins living in this bay. Only a few dozen use sponges to keep from scraping their noses, and that offered researchers an opportunity to compare creatures that use tools to others of the same species that do not.
Although these dolphins all appear to be related, researchers at the University of New South Wales suggest that nurture, not nature, is the reason these dolphins use tools, ruling out genetic explanations for the behavior. Instead, they are convinced that the use of sponges is passed from one generation to the next through imitation. Among bottlenose dolphins, mothers nurse their young for up to eight years, ample time for calves to absorb their mother's hunting tricks by observation. "This is an example of culture among these animals," says Dr. Bearzi. This is part of the reason it is so important.'
So far, almost all of the dolphin spongers have proven to be female. "The sex difference is really striking," says Dr. Mann. 'l don't know of another species where it is so dramatic.' of the sponge offspring, only the daughters could be seen still sponging once they reached maturity. The sons tried it but almost always abandoned It. Male dolphins rarely play a role In child rearing and tend to fish in packs.
For Dr. Mann, the discovery that dolphins, too, are tool users adds an unexpected dimension to the history of innovation, shedding new light on animal intelligence. Clever mimics and fast learners, dolphins have unusually large brains - four times the Size of a chimpanzee's and second only to humans in relative size, 'It speaks to this whole issue of creativity and learning and brain size,' she says. The number one question that drives me and others is: Why do dolphins have such big brains? What are they doing down there in the water that requires them to be so smart?'
