Entering the World of Dolphins:

Research So Compelling That Andy Read Rarely Takes a Holiday p.3

Dolphins aren't just fathead sound emitters. There is plenty of potential brainpower in their bulbous craniums too. "A dolphin brain is probably equivalent in size to a human brain," Read said. "But, having a big brain doesn't mean you necessarily do that much with it," he cautions. "They are clearly very bright creatures, capable of developing novel approaches to problems and combining concepts in ways that most other animals can't. They also do things that humans don't do in terms of learning to interpret and emit sounds. There is clear evidence that they make sounds that enable them to identify each other and mimic each other's sounds. But there is no evidence that they have a language. Maybe they do but we just don't know."

Language aside, scientists do know that dolphins have "individually stereotyped whistles that allow them to identify each other," Read said. "They learn these whistles when they're young." That's significant because vocal behavior is instinctive rather than learned in most mammals. In Australia's Shark Bay, dolphins have also been observed teaching their calves how to use primitive tools. Those babies learn how to carry sponges on their rostra, the dolphin equivalents of noses. "We think that they use sponges to pull fish out of crevices in corals, where there may be either poisonous fish or very sharp corals," he adds.

In places as widespread as Australia, South Carolina and Georgia, dolphins are known to work in groups to herd schools of fish onto mud banks-the better to eat them while they're trapped and flapping. "That requires coordination and, again, it's learned behavior," he said. "Females teach their calves how to do it." In a part of Florida Bay, the clear water area between the keys and the Florida peninsula's tip, dolphins create curtains of mud with their flippers and tails to encircle tasty mullets in fish corrals. "Then a series of dolphins will sit with their heads out of the water and their mouths open waiting for the fish to jump over the top of the mud plume," notes Read, who has a doctoral student preparing to work there. "For some reason the fish won't swim through the plume."

Damon Gannon, another doctoral student working under Read, is investigating whether dolphins identify and seek out food sources by the sounds those fish make. Gannon's work follows up on a Florida researcher's discovery that most dolphin fish prey are noise-making species. Doing his own North Carolina study of what dolphins eat, Gannon found that is even more the case in the Neuse River estuary near Beaufort. Bottlenose dolphin diets there consist mostly of croakers, which-as their names imply-are champion noisemakers. Croakers are unusually indiscriminate in that "both males and females possess the apparatus for making sound," Gannon said. Among other members of the drum fish family, "it's only the males who make sound, and they only do it during the spawning season."

By making recordings of underwater sounds and immediately trawling for fish samples, he learned that Neuse River croakers start their noisemaking at a very young age. Moreover, croakers there occur "in the size range that the dolphins eat." As a next step, he plans to take his croaker recordings to Sarasota Bay on Central Florida's west coast, where dolphin behavior can be observed in water much clearer than the murky confines of the Neuse River's mouth. A pan-and-tilt video camera will observe the dolphins' responses from the small tethered overhead blimp while a research boat broadcasts croaker sounds into the bay.

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