It often surprises me how seemingly unfussy frogs are with their spawning grounds. I have seen them in road ditches in Scotland and even taking to an old ceramic toilet buried and filled in a previous garden of mine. On the corner of our village road is a rather sad, shallow pond – or more accurately a large muddy puddle choked with leaf detritus, rubbish and even occasionally the odd fridge. Earlier this month however, ‘Top Town Pond’, as it is called locally(1), was choked by something very different and far more welcome - by frogs making their annual frenzied return and all the more obvious in the few inches of water.
So what makes them choose what seems at face value to be a less than attractive location for their spring romance and productivity? The first evidence that I have noted is that there are always small fish present, even in the height of summer when you might expect this pond to dry out. According to locals the pond is fed by continually by a spring from the nearby Dumble, “a stream which has formed a deep wide channel in the clay that is quite out of proportion to the amount of water normally carried”(1). So although the pond more than halves in volume in hot weather, it never completely dries out making it a safe haven for tadpoles to complete their aquatic life cycle. Another factor is the age of the pond - Many amphibians are loyal to their birthplace, potentially using a number of sensory mechanisms to return each year, such as; odours of ponds, landmarks, the positions of sun, moon and stars, and the earth's magnetic field (2). This pond has certainly been there for a long term, and indeed perhaps its presence determined the location of the Pinfold itself as in times past it served to quench the thirst of stray cattle that would be temporarily placed there awaiting their owners to reclaim them(1). Of course the dramatic decline in ponds over recent decades has meant that our amphibians have had to become less fussy – why else would they use my old toilet!
The pond has now returned to relative calm whilst the clumps of abandoned jellied eggs slowly warm in the rising spring temperatures. In a few weeks however the shallow waters will be churning again to movement of black tadpole shoals overshadowing the resident minnows.
(1) The Westhorpe Dumble Heritage Trail (see http://www.newark-sherwooddc.gov.uk/ppimageupload/Image81741.PDF) (2) Sinsch, U. (1990) Migration and orientation in anuran amphibians. Ethology Ecology & Evolution, 2 (1): 65 - 79