Dolphinshavebeenknowntoplaysometimeswithandcarryspong...

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Dolphins have been known to play sometimes with and carry sponges(海绵)over their noses, but researchers have been at a loss to explain precisely why.

Now, a recent study by Australian researchers may have uncovered the reason.

Sightings of dolphins carrying sponges on their noses while hunting fish from the rocky ocean floor have been recorded since the 1980s.

Researchers at the University of New South Wales used computer modeling of behavior to explore how long the interesting behavior, believed to provide protection against nose injuries, has gone on.

“In animal species that use tools, usually the entire population uses the tools. But in this case, only about five percent of the dolphins living in the bay use the sponges as a tool,” said Anna Kopps at the University of New South Wales Evolution Ecologist Research Centre.

The research also shows that nearly all the spongers are female. Scientists believe one single female started sponging in Shark Bay and all her descendants(后代)in the area---now the home of around three thousand dolphins—learned the behavior from their mothers. The sponging has been going to for some hundred eighty years.

“It’s interesting that the behavior doesn’t spread to the entire population and it doesn’t go extinct either,” said Kopps.

Dolphin descendants are dependent to their mothers for about four years, giving them enough time to observe and learn survival techniques.

While male dolphins also learn sponging from their mothers, the study found they learn the technique slowly.

“Some males use it but it will be a dead end because dolphins don’t learn form the dads,” Kopps said.

Despite the seeming usefulness of the technique, the researchers found it may not be a more successful technique than other hunting methods. “Regardless, sponging appears to be just as good as any other hunting technique,” said Kopps. “It turns out the cleverest of the sea world can also be tool-using lovers, spending more time hunting with tools than any non-human animal.”

The research is fascinating, but the question of whether tool use is particularly advantageous remains unanswered.

28. Why do some dolphins carry sponges while hunting fish according to the study?

A. To protect themselves

B. To cure nose injuries

C. To catch more fish

D. To have some fun

29. Scientists believe that the sponging behavior __________.

A. is passed down by mother dolphins

B. is now in danger of disappearing

C. has existed for about thirty years

D. is unique to female dolphins

30. It seems that male dolphins __________.