Another Life: Will natterjacks thrive in a fiery future?

Michael Viney: Climate change is expected to lead to more variable and intense rainfall, with longer periods of drought in between

Among hundreds of natterjack toadlets released at Castlegregory last month were some of the first to be raised from toads in captivity. This was the latest development in 30 years of conserving a rare and threatened Irish species.

A recent projection of the animal’s future, however, has suggested the toad could prove “a climate change winner”, even in a landscape heating up by a forecasted 2.6 to 4.1 degrees for this century. Such a temperature range could be catastrophic for much else in the human and natural world.

The natterjack is a fist-sized amphibian with warty skin and a yellow stripe down its back. It doesn’t hop, but can scamper quite fast after insect prey. Emerging from a sandy burrow in a summer dusk, it joins in a piercing, communal croaking that is one of the loudest sounds from Irish wildlife.

A “Lusitanian” species, fully at home in Iberia, it survived the end of the last ice age to pioneer isolated colonies on sandy heaths and dunes across northern Europe to the Kerry peninsulas of Ireland.

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The natterjack breeds in ponds, ideally shallow and temporary enough to lack the larvae of dragonflies and diving beetles that prey on the black toad tadpoles. These hatch from a single string of spawn, perhaps of several thousand eggs. They are vulnerable to fungal infection and, together with predation and ponds drying out, natural mortality can reach 90 per cent.

The toads’ main Irish refuges in modern times have been on the coasts of Kerry’s Dingle Peninsula and at Castlemaine Harbour to the south.

In 1991 the creation of a golf course near Castlegregory, with deeper, permanent ponds, prompted the Council of Europe to seek appraisal of Kerry’s natterjacks by Dr Trevor Beebee of the University of Sussex, a leading authority on amphibians.

“Most of Ireland’s surviving natterjacks,” he said, “have persisted by luck rather than as a result of positive conservation effort.” He estimated that the toads’ range in Kerry more than halved in the 20th century, a time of steady loss of Ireland’s farmland ponds

In the National Parks and Wildlife Service, the challenge was taken up by amphibian specialist Dr Ferdia Marnell. Since 2008 he has overseen the creation of more than 100 new, shallow ponds dug by farmers for payment. Their essential surround of short, well-grazed sward has, however, been hard to secure and maintain.

Over recent years, egg strings were down by some two-thirds, with most produced at traditional sites such as the Maharees, on the north of the Dingle Peninsula.

Another vital part of conservation, which began in the long, hot summer of 2018, has been to take spawn and tadpoles from shrinking ponds, rear them in the Dingle Oceanworld aquarium and tanks at Fota Wildlife Park and return the toadlets — about 600 so far — to more promising waters.

In a further, significant development, some of this year’s toadlet releases were spawned by mature natterjacks held at Fota as part of the zoo’s activity in captive breeding.

The natterjack “has the potential to be a climate change winner, notwithstanding unpredictable habitat and land-use change, sea-level rise inducing coastal erosion, changes in invertebrate prey abundance, and disease”

Meanwhile, Dr Ferdia Marnell has worked with Dr Marina Reyne of Queen’s University Belfast and a student team to model the possible reversal of Irish natterjack decline by “predicted positive effects of climate change”.

In the journal Ecology and Evolution (doi.org/10.1002/ece3.7362), they suggest that, given the present range of climate variation of northern natterjack sites, predicted temperature rises could increase the toads’ range, most notably in Scandinavia and the Baltic but also in Ireland.

Climate change is expected to lead to more variable and intense rainfall, with longer periods of drought in between. More winter rain makes more ponds in typical toad habitat, and this, with earlier springs, promises more egg strings in the toad’s Irish range.

The team calculated that in the higher scenario of CO2 emissions, with temperature increases of up to 4.1 degrees, egg strings could quadruple by 2070. Along with conservation measures, “assisted migration” could spread the natterjacks’ Irish range.

The paper concludes, indeed, that the natterjack “has the potential to be a climate change winner, notwithstanding unpredictable habitat and land-use change, sea-level rise inducing coastal erosion, changes in invertebrate prey abundance, and disease”.

Climate scientists admit that such projections can be swiftly overtaken by new research and the unexplored unknowns of adaptation. The paper, published more than a year ago, readily confesses that its predictions “may be of limited utility”.

They have certainly left me wondering how toadlets in their shallow, sandy-bottomed ponds will cope with the fiery future already on display in Britain and far beyond.