Grow your own croak park

That balmy, even clammy, Saharan spell of weather found a suitably copulatory scene in the pond, where the frogs had been hard at it for best part of a week.

A head count of 100 or so little bronze paperweights and door knockers is now standard for mid-February but fecundity this year is up a bit: 30-odd clumps of tapioca now glisten at the shallow end.

The worldwide concern about amphibian declines that overtook zoologists in the early 1990s has had the effect of focusing attention, both amateur and scientific, on Ireland's apparently flourishing population of Rana temporaria. Last spring, the Irish Peatland Conservation Council organised the first-ever national survey of frogs, collecting records from 900 schoolchildren all over the country. As data for science it's rather shaky but still encouraging to know that Ballinacarrig, Co Carlow, for example, could muster 415 clumps of frogspawn containing 83,000 eggs, or that the frogs of Co Wicklow were still breeding high in the hills, at 450 metres. A repeat survey planned for five years' time could show some interesting changes.

Acid rain, climatic changes and pesticide pollution have been blamed for amphibian declines. Anything that affects water quality, or the growth of algae in the spring, changes the frog's environment and food supply. Loss of habitat, too, has inevitable impact, so that in Britain, for example, the garden pond is increasingly substituting for the hundreds of ponds filled in on farms.

But why is it that some ponds have frogs and others don't? Why should I have dozens of frogs thrashing about between the bogbean plants and the water-lilies, while other gardeners, hoping for unpaid helpers in slug-control, can't seem to tempt any at all?

Some of the answers emerge in the first scientific study of the habitats in Ireland of both the common frog and the smooth newt, so often found sharing the same ponds in spring. It is the work of Dr Ferdia Marnell, now of Duchas, the heritage service. He has sampled some 280 watery places across the country - and, indeed, hoisted a squirming newt from the depths of my own pond at the first dip of his net.

His study is especially interesting because of the ecological situation of these two amphibians in Ireland. First, they're both at the western edge of their range. The smooth newt probably arrived here naturally after the last glaciation; the common frog may be a native, too, but was probably introduced in any case, brought in by the Normans for food.

The second special factor is that neither animal in Ireland has to face any competition from other species in the same family. In much of Britain, the smooth newt has two other newts (crested and palmate) to contend with. In Europe, the common frog overlaps with five other frog species. It could be that, in Ireland, smooth newt and common frog have come nearer to occupying the breeding habitats that really suit them.

Dr Marnell's study looks for the differences between sites that have frogs and sites that don't. Constructing the ideal frog habitat from his list of parameters shows the importance of the little bit of landscape close around the pond. The breeding orgy itself may only last a few nights, after which the adult frogs move away from the pond and forage on land for beetles, slugs and snails, caterpillars and flies.

What seems to be important, even crucial, is the existence close by of rotting logs and tree stumps, with small stands of scrub and long grass for cover. That sounds a fairly wild habitat but happens to fit my acre remarkably well. Many ordinary gardens, too, that are not excessively tidy, would offer a similar structure of deadwood and plant growth. The smooth newt likes scrub, too, but fights shy of grass cover. It was also more common in the ponds with more open water.

Unlike other researchers, Ferdia Marnell didn't find that his amphibians avoided ponds with fish. But he does confirm the appetite of breeding newts for the tadpoles of frogs. In fact, the newts choose a pond partly because the frogs are in it: a conclusion in which "discriminant analysis" accords well with common sense.

The smooth newt in Ireland does, however, avoid the acid water of bog pools, a habitat in which the common frog is quite happy - indeed, it is the most important predator in bogland ecosystems in Ireland (all those midge larvae). And there, of course, it is preyed upon by herons, who spend late February hunched above the lonely flashes of water, stabbing at their leisure at nature's lavish take-away.

Which brings me to the renewed angst over a proposal for a Clifden airstrip at the margin of Roundstone Bog. This was turned down once but a deal now being considered would swap the original 80 acres of relatively undamaged bog for an airstrip on the derelict Marconi site at Derrygimlagh, already owned by the State.

Tim Robinson and the local conservation group are deeply suspicious of any compromise which would "intrude on the silent beauty of this unique tract of wilderness" and rob the Roundstone Bog of an essential buffer zone. The conservation of an eco-system as fragile as this needs a careful transition to the more developed world around it and the Roundstone group fears it could prove "the thin end of the wedge".

Michael Gibbons, the Clifden archaeologist and eco-tour leader, equates this attitude with "scaremongering" and cannot see why anyone would oppose the deal "on anything but philosophical grounds". Each man puts his case at a Connemara website on the Internet: www.connemara.com. (go down to "Words"). The Minister for Arts, Heritage and the Gaeltacht, Ms ile de Valera, has invited views from the public and Monday is the last day for receiving them. They will reach her through Duchas at 51 St Stephen's Green, Dublin 2 (e-mail: duchas@indigo.ie; fax: 016611612).