Worcestershire Record No. 4 May 1998 p. 10
The Marsh Frog Rana ridibunda is an introduced species in Britain and is now well established in Kent and Surrey where noisy colonies regularly disturb people by croaking loudly and incessantly during late May and June.
The Pool Frog Rana lessonae may be a true native British species but controversy still rages over the colony in Norfolk which maybe a relict population or may be introduced.
The Edible Frog Rana esculenta is a fertile hybrid between the other two.
All are classed as Green Frogs while our Common or Grass Frog Rana temporaria is included in the Brown Frogs. This is how things are in Europe, and normally in Worcestershire we only encounter the Common Frog. So, as this goes to press, Will Watson and Alan Shepherd are frantically attempting to capture a Green Frog which has turned up at a fishing lake complex within the County, in order to establish its exact identity, with limited success.
You see, in order to distinguish between the three species one needs to examine the coloration of the back legs, and to be really certain one pushes the back legs together and see if they meet or overlap. Or you can tell the difference by feeding a recording of the croaking into an oscilloscope. Easy ... except that both are extremely aquatic and wary and are usually seen as a streak that plops into the water from its sunning spot when you get within two metres ... and they start croaking at about 9 pm on warm evenings, but seem to have a sixth sense about tape recorders.
We are in touch with colleagues in Kent and Surrey, one of whom can tell them apart by their calls without recourse to an oscilloscope but at the moment it's a case of "Watch This Space" in the next BRC newsletter!
|Arnold EN & Burton JA (1978) A Field Guide to the reptiles and amphibians of Britain and Europe. Collins|
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