The Recovery Of England’s Forgotten Frog

How England’s pool frog went from an overlooked amphibian to a top conservation priority raises important questions about our perceptions—or misperceptions—of which species are native whilst revealing the subtle beauty of a forgotten frog

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The English have long been fascinated with nature, especially collecting and identifying their local flora and fauna. So the idea that any living thing — especially a vertebrate — anywhere in England could go unrecognized as a native species is quite astounding. But apparently, this is exactly what happened for the pool frog, Pelophylax lessonae.

The “peculiarly loud and somewhat musical sound” uttered by singing pool frogs was a common and distinctive sound for decades throughout the wetlands of east England. But everyone assumed this frog species had been introduced from mainland Europe — a common, albeit peculiar, pastime indulged in by Victorian naturalists — so no one really cared when it began to fall silent. By the late 1990s, it was too late: pool frogs had disappeared from Thompson Common, their final home in England.

About the same time that this species was disappearing from England, a group of researchers came together to address the mystery of this frog’s origins (ref): was it a native species or was it introduced? Dilemmas such as this are not uncommon and are most likely to arise near the edges of a species’ range. A decision about a species’ native-or-not status has dramatic implications for whether to reintroduce and conserve a particular species.

“I think the pool frog is particularly exciting”, said Tony Gent, who is the Chief Executive Officer of the Amphibian and Reptile Conservation (ARC), based in Bournemouth, Dorset. “The idea of bringing together disparate sorts of information to prove an animal that’s gone extinct is native is fairly unique.”

The research team, comprised of experts in a variety of disciplines, examined the frog’s bioacoustics, genetics, ecology and even the anatomy of its subfossil bones, and discovered that the pool frog was actually native to England. The evidence revealed that pool frogs became established in England after crossing the ancient land bridge from Europe (ref). This land bridge, known as Doggerland, was the victim of rising sea levels, and finally submerged beneath the waves around 6150 BC.

Currently, the pool frog is one of only four amphibian species recognized by the UK government as protected under its Biodiversity Action Plan (ref). The frog’s populations declined after human invasions into the Fenland and Breckland areas of East Anglia led to deterioration of its wetland habitat, although air pollution also contributes by causing over-nitrification of pond waters.

After the research showed the extinct pool frog to be a native British species, the ARC and its collaborators went to work. They started by restoring its habitat and implementing rigorous biosecurity protocols so they could safely fly a group of frogs across the North Sea to re-establish a native population. They then captured pool frogs, tadpoles and spawn in Sweden, where its closest relatives still live, and brought them to a secret location in Norfolk in 2005, hoping to re-establish a small colony there. Tadpoles produced by that secret population were relocated and released in Thompson Common in 2015. Thompson Common is perfect for these frogs: it’s filled with small glacial relict ponds, known as ‘pingos’ (from an Inuit word for a conical hill). Pingo ponds hold fresh water throughout the year and thus, are an ideal location for sun-loving pool frogs.

So far, the future looks bright for the pool frog. Although listed as Critically Endangered, the frogs appear to be establishing a self-sustaining population that is moving outward from the ponds where they were initially re-introduced.

“It is not often that you can say that you brought an animal back from extinction, but that is exactly what we have achieved with our partners and with funding from the government’s Green Recovery Challenge Fund”, said Jim Foster, conservation director at ARC.

This sensitive bioGraphic mini-documentary by filmmaker Katie Garrett tells the story of England’s almost-forgotten pool frog and the conservation efforts that brought it back home.

This video originally appeared in bioGraphic, an independent magazine about nature and conservation powered by the California Academy of Sciences.

Source:

Trevor J. C. Beebee, John Buckley, Ivor Evans, Jim P. Foster, Antony H. Gent, Chris P. Gleed-Owen, Geoffrey Kelly, Graham Rowe, Charles Snell, Julia T. Wycherley & Inga Zeisset (2005). Neglected native or undesirable alien? Resolution of a conservation dilemma concerning the pool frog Rana lessonae, Biodiversity and Conservation 14:1607–1626 | doi:10.1007/s10531-004-0532-3

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