An evocative peeping echoes across a large, sunny aviary. The distinctive call of the curlew comes from dozens of chicks, who strut through long grass squabbling over a much-prized worm.
The scruffy-looking chicks with the beautiful voices may be the best hope for the endangered species, whose numbers have halved in the past 25 years as it vanishes from lowland England.
Nearly 100 birds are now being “headstarted” – hatched in captivity from eggs rescued from airfield runways. Until last year these nests were destroyed under government licence because of the danger that Europe’s largest wading bird would collide with a jet.
The curlew are being released in Dartmoor and Norfolk in an attempt to stop the species becoming extinct as a breeding species in the south. After a pilot last year in which 79 were released, dozens more will be taken next month to acclimatise at release sites including the Queen’s Sandringham estate and Wild Ken Hill in west Norfolk, in a project led by Natural England, the government’s conservation watchdog.
The curlew is in trouble because of its disastrous fledging success rate: just 0.2 fledglings a year per pair survive. Each pair produces on average only one fledged chick every five years at best.
Curlews nest on the ground, where chicks are destroyed by more frequent silage-cutting but also by predators such as foxes.
Because it is a long-lived bird, the curlew needs a fledging success rate of 0.4 to 0.6 to become sustainable. In captivity the rate is almost 100% thanks to the work of Chrissie Kelley, the head of species management at Pensthorpe Conservation Trust in Norfolk. The Wildfowl and Wetlands Trust is also headstarting curlew at its base in Gloucestershire.
After collection, eggs are placed in incubators, which automatically turn each egg and regulate heat and humidity. Newly hatched chicks are given heat lamps and “mop mums” – the heads of a floor mop, in which the chick nestles. “They’ll wriggle into it – it gives them an extra place to hide away,” said Kelley.
Five-day-old chicks are placed in large outdoor pens where they can learn to find food themselves, their diet boosted by a pellet developed in Germany for wading birds.
“They are fantastic to rear just being such keen natural foragers. There’s no issue with getting them to eat and they always want to explore new ground so they are quite a joy,” said Kelley. “Headstarting can help that really difficult period. The great thing about this project is that none of these birds would have even got to hatch, so it’s a win-win. But it doesn’t solve the problem – we still need to manage their natural habitat.”
The idea to embrace headstarting rather than simply issue licences to destroy the nests was made by Graham Irving, of Natural England’s licensing team, working with Richard Saunders, a senior ornithologist at Natural England.
Airfields are one of the best places for curlew to nest in southern England because large swaths of grassland mimic the steppe, and perimeter fences ensure few foxes threaten the nests.
Since the project began last year with the support of the RAF and the Defence Infrastructure Organisation, the military and civil airfields where curlew nest have shifted to curlew-friendly grassland management. Increased monitoring means that dozens more nests are being discovered. Not all nests need to be relocated for headstarting.
There were fears that released birds would fly off and breed in Scandinavia but Saunders said the early signs were promising. Although birds released in Norfolk have been identified from their colour rings on their legs in Devon, Somerset and Lincolnshire, some have settled close to the release sites – chosen for offering good habitat, as well as some predator control by gamekeepers.
According to Saunders, there is a shortage of 10,000 fledgling curlew to make the population sustainable across Britain. “Headstarting can’t contribute a massive proportion of that 10,000 deficit in fledged chicks but in lowland areas we’re hoping it can help maintain the bird’s distribution. It might be a vital tool to ensure these lowland populations hang on.”
Samantha Franks, a senior research ecologist at the British Trust for Ornithology (BTO), is monitoring the impact of headstarting. “Fundamentally, everything goes back to land-use,” she said. “Agricultural intensification means a shortage of habitat. More earlier mowing and more silage cuts mean the habitat isn’t as good as it used to be. Increased predation pressure comes because the habitat is more conducive to predators now such as foxes.”
According to Franks, it is unlikely that lowland England will ever return to the low-impact farming of, for instance, the Hebrides, where curlew thrive, but the bird’s future could be secured by providing “really, really good pockets of habitat where relatively big populations can survive”.
Alan Law, the chief officer for strategy at Natural England, said: “A lot of conservation in the last 30 years has been about holding the line, stemming the decline, but we know that for species to thrive we need to have larger areas and viable populations. Headstarting alone won’t restore lowland breeding populations – we’ll have to invest in that wider landscape health and resilience if we are to see curlew thrive in the next 50 years – but it’s a vital short-term step.”