Science Magazine - Why dolphins wear sponges

In 1991, researchers spotted dolphins doing something unusual in Shark Bay, Western Australia. When the animals got hungry, they ripped a marine basket sponge from the sea floor and fitted it over their beaks like a person would fit a glove over a hand. The scientists suspected that as the dolphins foraged for fish, the sponges protected their beaks, or rostra, from the rocks and broken chunks of coral that litter the sea floor, making this behavior the first example of tool use in this species. But why do dolphins go to all of this trouble when they could simply snag a fish from the open sea?

Patterson's and Mann's results also "reinforce a pattern" often seen in other tool-using animals, says Simon Reader, a behavioral biologist at McGill University in Montreal, Canada. "Tool use appears to be almost a last option, taken when other options fail or are unavailable," he says, noting that woodpecker finches in the Galápagos Islands "turn to tool use only in arid areas," wielding cactus spines to extract grubs from tree branches. Using tools takes time and energy, Reader says, and animals tend to rely on them only when there's a guaranteed payoff, such as turning up a fatty fish that most other dolphins (and fishermen) know nothing about.