Some of the most familiar wading birds flocking to UK estuaries in winter have seen major declines in the past decade, conservationists have warned.
The latest results from the Wetland Bird Survey have revealed that ringed plovers, redshanks, dunlin, curlew and oystercatchers, which are all among the eight most abundant winter wading bird species in the UK, have all seen populations drop significantly.
Ringed plovers have suffered declines of almost two fifths (39%) in 10 years, while redshank numbers fell by more than a quarter (26%) and the situation for dunlin is almost as bad, with declines of 23%.
Curlew numbers have fallen 17% and oystercatcher numbers are down 15% in the 10 years to June 2012, according to the Wetland Bird Survey, which involves data collected by thousands of volunteers.
The most abundant waders found on UK estuaries in winter are dunlin, with an estimated 350,000 birds, oystercatcher, with around 320,000 individuals, and knot, with 320,000 birds. Knots have also seen numbers decline, by 7% in 10 years.
But there is good news for species that were relatively scarce a few decades ago, with avocet numbers rising by 61% in a decade and black-tailed godwits increasing by 57%.
Wildlife experts said the reasons for the declines of some of the most abundant wintering waders on UK estuaries were not fully understood, but it was likely to be due to a combination of factors.
Waterbird counts from across north west Europe show that species are shifting north-eastwards in response to milder winters.
Winter population declines in the UK may also be due to fewer young waders being successfully bred and reared in the Arctic, which is experiencing rapid warming.
Richard Hearn, head of species monitoring at the Wildfowl and Wetlands Trust (WWT), said: "The declines in waders and other wintering waterbirds in the UK over the past decade or more, as revealed by the Wetland Bird Survey, are indicative of wider concerns about the state of our environment.
"They demonstrate the unprecedented period of change that these waterbirds are undergoing, and highlight the need for a step change in monitoring and relevant conservation action if we are to avert continued biodiversity loss."
Millions of waterbirds spend the winter on the UK's wetlands, particularly estuaries which provide a rich source of food and many of which are legally protected.
Around 15 species of waders winter on UK estuaries in internationally important numbers, with at least one estuary supporting more than 1% of the international population.
UK estuaries are also important to many wildfowl such as geese and swans, and other wader species which are present in smaller numbers during the winter or passing through in spring and autumn.
The Wetland Bird Survey, a partnership between the British Trust for Ornithology (BTO), the Government's advisory Joint Nature Conservation Committee (JNCC) and the RSPB, in association with WWT, monitors birds at more than 2,000 wetland sites from estuaries to ponds across the UK.