Nature is reclaiming its territory at a quarry in the east of England, which is being converted into a vast reserve that will provide vital sanctuary to endangered birds.

The marshy plain of the Fens outside Cambridge, with its reedbed wetlands, has become an attractive habitat for the secretive bittern, which was on the UK's Red List of most-threatened species until 2015.

The thickset heron, with its perfectly camouflaged streaked brown plumage and a booming springtime call that sounds like someone blowing over the top of a bottle, is now on the Amber list, which is less critical but still threatened.

"It's really a demonstration of how working with partners -- big decisive action at large scale -- we can bring species off that Red list," said Chris Hudson, Senior Site Manager at the Royal Society for the Protection of Birds' (RSPB) Ouse Fen Nature Reserve, some 120 kilometers (80 miles) north of London.

Although the elusive bird did not appear when AFP visited on a brisk and rainy January winter morning, Ouse Fen now houses 5% of the UK's bitterns.

The reserve's bittern population is now larger than the national total in the mid-1990s, when the RSPB's list of threatened species was first published, according to Hudson, who keeps binoculars at the ready.

Decline in insects

The most recent edition of Birds of Conservation Concern was released in December 2021, and it now includes 70 species on the Red List, which is more than double the number when the first report was published in 1996.

Around 30% of the British Isles' 245 bird species are now threatened.

The house martin and swift, migratory birds that fly thousands of kilometers (miles) from central and southern Africa to breed in Europe each spring, are among the new species on the list.

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The RSPB Centre for Conservation Science's Head of Monitoring, Richard Gregory, blames population declines primarily on changing land use in the UK, Europe, and beyond, which deprives birds of food and habitat.

"The decline of these birds might tell us something about a huge decline in the biomass of insects, which has been a real concern for conservationists across Europe recently, and it's probably a much wider phenomenon," he said.

"So we need more research, but that's a real warning sign about how the environment is changing around us."

"But we also know that when you manage the habitats, when you protect the habitats, and you protect the birds, they can bounce right back," said Gregory, pointing to the example of the white-tailed eagle, which was extinct in the British Isles in the early 20th century.

This imposing bird of prey is no longer on the Red List thanks to a successful conservation and reintroduction program, and there are now at least 123 pairs of these large sea eagles in the UK.

Make conditions right 

In early January, the Ouse Fen reserve was home to once-rare great white egrets of the heron family and marsh harriers, a threatened bird of prey whose numbers have increased thanks to decades of conservation efforts.

The mix of reedbeds, open water, and grassland, which opened in 2010 and attracts 20,000 visitors per year, is being restored on land that was previously used as Europe's largest sand and gravel quarry.

Over the course of the project, approximately 28 million tonnes of aggregate will be extracted from the ground, leaving holes that are now filled with water and reeds, much to the delight of the birds.

"Our job here was to recreate the right habitat conditions that would bring the bittern back," Hudson said. These include "lots of feeding opportunities to get their prey sources like fish, and particularly eels."

"Once we've put those conditions in place, that effectively brings the birds back. 'If you build it they will come' is the phrase that we quite often use."

Humans alter the landscape by creating bodies of water and planting reeds, and "nature will look after the rest and come back quite naturally if given that opportunity," he said.

"Give nature a chance and it will return," he concluded.