Travelling around the marsh at the moment is frustrating. For once the place really lives up to its name, with extensive areas of flooded fields, so why are there so few common frogs Rana temporaria out there?
Its obvious I hear you say - those European marsh frogs Pelophylax ridibundus* have eaten them all. The great British herpetologist, Malcolm Smith reported declines in common frogs and toads after their introduction. I am not so sure though.
Just to the north of Lewes there is an area of grazing marsh with good numbers of both species. Perhaps something about our grazing marsh habitat does not suit the common frog these days?
At Pevensey Levels National Nature Reserve there are (or were 8 years ago) areas where common frogs really live up to their name. I have counted rafts of frog spawn containing 300 spawn clumps. The reason lies in the fields where they breed, rather than the ditches. They have low lying hollows that flood in the winter. Such temporary wetlands are just what common frogs need. They breed early in the year, and then its a race against time to develop before the floods dry out. Risky, but such pools do not contain predatory fish. In a wet year they can produce far more froglets than a fish-filled ditch.
Sadly these features are really rare on our well drained marshes. So often the winter flashes are drained to enable water to retreat quickly into the ditches. Those areas that are wet, as at Fairfield, are often rather brackish and not ideal. Its a feature that is easily created though, and does not need to be that large. So if there are any farmers or conservation managers looking for a project try blocking up the odd drain in your pastures. Or excavate out a hollow in a low lying sump. This is particularly likely to work if the wetland is close to a built up area, where many of our remaining frogs are able to hang out these days, thanks to garden ponds.
* Yes the taxonomists have been at it again - several of our amphibians and reptiles have been renamed.