Environment

Michael Viney: Irish frogs and their explosive breeding

Another Life: Bounty of spawn in ditches and ponds provides food for animals and birds

Michael Viney's face
Michael Viney
Sat Feb 26 2022 - 06:00

From almost the start of the year, the mating of frogs began to spark gleams of spawn in the wetlands of Ireland, starting in the southwest and travelling north with the newer frontiers of spring.

At up to 4,000 eggs in a clump, and countless clumps to the hectare, a basic takeaway for the predators of nature was well launched and continues still, encouraged by the filldyke rains of February.

Once, in March, on the lower, rocky slopes of Mweelrea in Co Mayo, I took note of a boggy place quite submerged in spawn: some 50 clumps in 2sq m welcomed as food in its successive froggy forms by everything from newts and diving beetles to pretty well every furry mammal, the crows and herons, egrets and kestrels.

This spring, however, I like to think, a good few netfuls of spawn will find at least temporary sanctuary in the classroom aquariums of primary and secondary schools.

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Such enlightened enterprise – once, it is claimed, a "tradition" of Irish rural education – was outlawed a few years ago by the inclusion of frogs in the EU's nature directives and thence in the Irish Wildlife Acts, both forbidding interference in froggy lives. The conflict was resolved by issuing a general licence from the National Parks and Wildlife Service (NPWS) allowing schools to collect frogspawn for study. Among the conditions is releasing the spawn (more likely, froglets) back to the wetland from which it was taken.

Paddy Madden, long a campaigner for nature in schools, reckons that keeping tadpoles in class is one of "the very few perks for being a primary-school teacher". His advice, along with books from Eanna Ní Lamhna and others, is part of abundant online help regarding setting up tanks and keeping them healthy.

It happens, sadly, that my sole recollection of school biology lessons, late in the second World War, was having a preserved dead frog shoved in front of me, cut open and splayed apart, the better to study its innards.

I wonder how today’s kids take learning about “amplexus”, the tight sexual clutch of the male frog on the female’s back, during which he impregnates release of spawn? My drawing, made during the heyday of our garden pond, suggests a seraphic union. It ignores the amphibian porn of the queue of males and their multiple mounts that can squeeze a female dead from exhaustion.

I do miss the pond, now a shrunken hollow enveloped in the shade of the beech tree. I took all that trouble to give its plastic liner a soft bed of sand from the shore and still, eventually, it sprang a leak that slowly drained the pond’s life. I miss the newts, arriving from nowhere, the great diving beetles and twirling water boatmen, and the pink flowering spikes of bogbean, bright as orchids.

Frog populations in many parts of the world have suffered huge decline from fungal and viral diseases and progressive loss of habitat. While no disease has reached Ireland, the steady obliteration of farm ponds and the sprawl of suburban development seems likely to support the anecdotal reports of local scarcities.

Despite two sampling surveys that seemed to find frogs where they should be, reports to Brussels from the NPWS found their future prospects “unfavourable”.

Proof for this, however, was clearly limited, and a first national survey in 2010 was designed with all the bells, whistles and arithmetic of the latest population algorithms. The fieldwork, too, most of it carried out by the nationwide network of NPWS wildlife wardens, was rigorous enough to need special training.

On selected bits of map ½km square, a total of 405 water bodies were surveyed for spawn, with three return visits to check on frog numbers and accumulating spawn. Everything was carefully estimated, including dimensions and depth of the water. There was spawn in half the water bodies and three-quarters of the survey squares, most abundant in Mayo, Sligo and Donegal.

On such rigorous calculation, the Republic had some 165 million frogs, happily mating almost anywhere there’s water, especially in the drainage ditches that edge the nation’s fields. They were probably the island’s most abundant vertebrate, next to the long-tailed field mouse.

This was not exactly a novel discovery – the concentration of Irish frogs in ditches and at the sides of streams in bogs was noted by scientists three decades ago. But the new survey made Ireland one of the few countries with a robust head-count of Europe’s common frog.

With an average of some two dozen per hectare, we come nowhere near Finland’s teeming densities (up to 80 per hectare) or even those of good habitats in Scotland. But it’s a healthy population, even sometimes “explosive” in breeding compared with the frogs of continental Europe. Its outlook has thus changed to “favourable”, to set against the many contrary concerns in conservation.

National Parks and Wildlife ServiceEanna Ní LamhnaPaddy Madden