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Last Updated: Friday, 14 November, 2003, 12:55 GMT
Frog croaks reveal regional bias
The pool frog rana lessonae, SPSS
Not all frog mating calls sound the same
To everyone but a frog, one croak probably sounds very like another.

But analysis of different croaks has revealed that at least one species of amphibian has developed regional accents in its mating calls.

The accented croaks are thought to have developed during the last ice age when populations of pool frogs were separated for thousands of years.

The discovery was made during a project to return an extinct species of pool frog to wetlands in Eastern England.

Sound start

The discovery of the frog accents was made by amphibian expert Julia Wycherley who was trying to find out which exact sub-species of pool frog (Rana lessonae) had been living in East Anglia before it became extinct.

Ms Wycherley has spent a lot of time listening to frog calls and was convinced that she could hear subtle differences in their mating sounds.

To back up her hunch, she analysed recordings of calls with software, from technology firm SPSS, usually used to reveal trends in human behaviour.

Ms Wycherley compared the length of the different calls, their amplitude and volume. She also looked at the length of separate features in the calls.

She found that pool frogs had three distinct accents that were directly related to their genetic heritage.

Coming back

Bernie Simmons, a spokesman for SPSS, said it was thought the frogs migrated to the warmer climate of southern Europe during the last ice age where they separated into distinct colonies that slowly started to diverge.

Part of that diversity has emerged as regional accents.

The accents are different depending on whether pool frogs belong to the ancient Iberian, Italian or Balkan populations.

"These are the places where the pool frogs hung out during the ice age," said Mr Simmons.

It was thought, said Mr Simmons, that the extinct East Anglian pool frogs would be from the Iberian population simply because Spain is geographically closer to Britain.

But, said Mr Simmons, analysis of fossil frogs from East Anglia showed that the missing group probably came from the Balkans.

"It's important to introduce absolutely the right species," said Mr Simmons. "If not, it will not thrive or develop a community that is self-sustaining."

Now English Nature is planning to acquire a population of Balkan pool frogs and re-introduce them to the East Anglian wetlands.

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