ORNITHOLOGISTS BEWARE: if you happen to visit Thompson Common nature reserve in May, you may be baffled by strange, birdlike calls you can’t quite place. This Norfolk Wildlife Trust haven, not far north of Thetford, is home to Britain’s rarest amphibian: the northern pool frog, which has a loud green stripe and a voice to match.
And soon we hope to hear that exotic ribbet on Woodland Trust turf, as we create a pool frog habitat at our fledgling wood next door. “We bought Green Farm for £2.2 million in 2021,” says Tom Bolderstone, who is leading the Woodland Trust’s project there. “At nearly 300 acres, it instantly became our largest site in Norfolk, and we’ll be planting up to 140,000 trees to transform it into woodland. But the really exciting bit is along the site’s border with Thompson Common. Thanks to £45,000 from Natural England’s Species Recovery Programme, we are working with the Norfolk Wildlife Trust to rediscover lost ponds on our side of the fence – in time, we hope the pool frogs will come hopping onto our patch.”
Pool frogs and pingos
Extinct in England by the 1990s, pool frogs were reintroduced from Sweden in 2005. “The last known colony was at Thompson Common,” explains John Baker of the Amphibian and Reptile Conservation Trust. “Conditions are perfect, thanks to the reserve’s 400 prehistoric ‘pingo ponds’ – glacial compressions formed in the last Ice Age. They are teeming with life: dragonflies, butterflies, beetles.
Laser scans suggest there are at least ten pingos on the Woodland Trust land too, waiting to be revived. Ponds like these make ideal breeding grounds for the extra-special croakers, but also for common frogs, toads and two of the UK’s three newt species – great crested and smooth. Their shallowness means they stay warm in spring and dry out now and then, removing fish. Hungry perch and trout can wipe out clouds of frogspawn or newt eggs with a single swipe.
Britain’s native amphibians
Britain has just seven native amphibians in all: those two frog species, a trio of newts (the third species is palmate), plus the common toad and much rarer natterjack – sadly now confined to around 50 sites.
The Woodland Trust has ponds tucked away in scores of our woods UK-wide, plus new ones in the pipeline at places like Top Wood, south of Burton-on Trent. Here, plans to reclaim an artificially buried stream will create a shining waterland of ponds and seasonal scrapes, ideal for the site’s great crested newts, a protected species.
David Logan, the Woodland Trust’s Top Wood custodian, says: “Tending ponds often entails thinning bankside trees, since they’re best for wildlife when they are not too shady or full of leaves. But that’s not to say amphibians don’t like woodland. At Top Wood, we plan to scatter lots of log piles coated with mud as hibernacula – that’s basically the Ritz for amphibians between breeding seasons.”
Toads
Toads in particular are keen woodlanders – these copper-eyed crawlers spend much of their year hunkering among deadwood, or foraging in the leaf litter for slugs, worms and insects. “Toads prefer deeper water to breed,” explains Woodland Trust conservationist Sally Bavin. “Their spawn, laid like strings of pearls, is toxic to fish, and so is their skin, so they can return to the same breeding pond year after year. Often that spring pilgrimage involves a perilous road crossing – at Haddon Wood in Somerset, Woodland Trust volunteers even run patrols to help them across.
What’s more, the relationship between toads and trees could be closer than once thought: in 2022, astonished wildlife surveyors discovered more than 50 of the warty wonders inside dormouse nest boxes and hollows normally favoured by bats – as high as three metres up in the canopy! “The reason is unclear,” says Bavin. “Could they be searching for food, or avoiding predators? But it again highlights why we must protect our veteran trees, with their cracks and cavities so vital for wildlife.”
Newts
Newts too deserve special attention, Bavin says, especially the great crested variety. “They have significantly declined, and are protected because Britain is a stronghold in terms of the global population. So it’s incumbent on us to nurture them here.”
Newts are sensitive to temperature, making them a valuable indicator of our warming climate’s effect on wildlife. The Woodland Trust’s citizen science project Nature’s Calendar tracks 179 ecological events each spring and autumn, and Bavin says the data suggests climate change is having an impact: “Our volunteers have recorded their first active newts as early as New Year’s Day. The best way to spot them is to shine a torch into your garden pond at night: you’ll see them creeping about in search of mates.”
Frogs and toads essentially leap on their partners, but male newts curl and flutter their tails to waft pheromones to their chosen female. Also look out for folded leaves: newts use their back legs to tuck each sticky egg tidily away in the weed. They rove more widely in summer – you may even find one chilling in your dog’s water bowl before carrying on its great garden insect hunt.
Finding the right home
Back in Norfolk, scientists from University College London are busy testing which of Green Farm’s lost pingo ponds could be viable. “We’re sending tubes underground to suss out their water levels,” explains Bolderstone. “So far, we’ve got six strong candidates. Perhaps by next spring we’ll be able to give those noisy northern pool frogs something to shout about!”
This article first appeared in Broadleaf, the magazine for members of the Woodland Trust. To find out more, visit http://woodlandtrust.org.uk/join and to learn more about volunteering with the Woodland Trust and Nature’s Calendar, visit http://woodlandtrust.org.uk/record.
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