Sydney  - Using tools used to be a distinguishing feature between humans and the rest of the animal kingdom. Then monkeys were spotted cracking nuts with stones.

More recently, birds have been seen using sticks to trick termites out of their mounds. Dolphins are the latest to join the ranks of the tool users.

Janet Mann, a biologist at Georgetown University in the United States, has catalogued the antics of the bottle nosed dolphin colony at Shark Bay on Australia's west coast.

Her findings, written up on the PlosOne science website, make interesting reading, particularly because tool-using is mostly confined to females and is a skill passed down largely from mothers to daughters.

Professor Mann found some dolphins using sponges to protect their noses as they foraged for food on the sandy bottom of the sea. They took time selecting the conical sponge that was the perfect fit for their beaks.

"Dolphins searched for up to 10 minutes for a sponge, transported sponges to foraging areas, and occasionally carried sponges in social groups for later use," Mann said.

Dolphins using sponges were more likely to spend time foraging on their own, and to dive to deeper depths for longer, than other dolphins. Mann termed the behaviour "sponging" and said "how and why dolphins sponge and whether the behaviour is cultural is under debate." (dpa)