Counting frogs and tadpoles' teeth
Moonlight serenade: frogs knotted in rapt amplexus. illustration by michael viney
ANOTHER LIFE: It was my 80th year to heaven and I walked abroad in a promised sunny spell, the surf on the shore calmed down at last, to see if the frogs had remembered my birthday. They got it spot on in 1997 (“garden pond full of frogs and first spawn laid”) and again in 2005, but since then I have lost the great gatherings that February used to bring of 100 or more shiny heads, knotted in rapt amplexus, pumping out mounds of jellied eggs to glisten in the sun.
The fault is all mine, as I let what remained of open water succumb to creeping grasses, toppling rushes, fallen leaves, in the pond’s clear haste to become a fen. Hauling out this matted biomass every autumn is now beyond me, so that, at the imminence of spring, the algal scents said to summon frogs to their mating pools must be quite overwhelmed. I suspect also that the last few loyal habitues have been hoovered up by the badger that visits us on tour in February, testing his weight on the pond’s strawy mattress.
I do not, it turns out, need to feel at all guilty about depriving Rana temporaria of its breeding habitat. The Republic, at a new and highly rigorous calculation for the National Parks and Wildlife Service (NPWS), has about 165 million frogs, happily mating almost anywhere there’s water, and above all in the drainage ditches that edge the nation’s fields. They are probably the island’s most abundant vertebrate, next to the long-tailed field mouse.
This new and cheering estimate replaces the apprehension favoured a few years ago, as frog populations in many parts of the world were seen to suffer huge decline from fungal and viral diseases as well as a progressive loss of habitat.
Although no disease had reached Ireland, the steady obliteration of farm ponds and the sprawl of suburban development seemed likely to support the anecdotal reports of local scarcities. Despite two sampling surveys that seemed to find frogs where they should be, NPWS reported an “unfavourable” conservation status for this protected species.
Proof for this, however, was clearly limited, and a first national survey was designed with all the bells, whistles and arithmetic of the latest population algorithms. (Aspiring young scientists may care to download the frog report from the NPWS website to see the sort of test they could be in for.)
The fieldwork, too, most of it carried out by the nationwide network of NPWS wildlife wardens, was rigorous enough to need special training.
It was based on a simple truth – where there’s frogspawn, there’s frogs – but making sure of comparable inspections on squares of land and water truly representative of the current surface of the Republic needed a sampling programme of some complexity. Since the turn of the 19th century, for example, the numbers of farmland ponds had halved, especially in eastern cereal-growing counties like Wexford, but about 2 per cent of the Republic was still good frog-breeding habitat, ranging from lakes and canals to dune slacks and roadside ditches. Everything needed sampling, to a scientific plan.