Birds decline partly due to clean up

A CLEAN-UP of one of East Anglia's most important river estuaries may be a factor in the decline of some species of water birds, new research suggests.

A CLEAN-UP of one of East Anglia's most important river estuaries may be a factor in the decline of some species of water birds, new research suggests.

Untreated sewage was pumped from Cliff Quay, Ipswich, into the Orwell Estuary until 1995.

But while the improvement in the water environment has helped some species, the reduction in nutrients being fed into the water may be responsible for reduced populations of invertebrate creatures - the food for birds such as redshank, dunlin and black-tailed godwit.

However, other factors for a decline in water birds in both the Orwell and Stour estuaries may be habitat loss, dredging and disturbance from recreational activity.


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The new research has been carried out by the British Trust for Ornithology using data collected by the Suffolk Wildlife trust over a 25 year period.

Eleven out of 17 bird species in the two estuaries, which form a Special Protection Area (SPA) under a European Union directive, were found to be in decline and eight had fallen by a quarter between 1994/5 and 1999/2000.

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The eight species are the great-crested grebe, cormorant, shelduck, pintail, ringed plover, dunlin, black-tailed godwit and redshank.

The new research suggests the Stour-Orwell SPA has an unusually high proportion of declining species compared with other estuarine SPAs in England and Wales.

“The indication is that something unusual must be occurring on the Stour-Orwell SPA,” said local Suffolk Wildlife Trust warden, Mick Wright.

Mr Wright, who has been involved with bird counts on the estuaries since the early 1980s, said the local data was among the best collected anywhere in the country and showed a definite decline in water birds.

“I notice it myself - there's not nearly so many birds feeding on the estuary now as there was a decade ago,” he added.

Mr Wright said the halt to the pumping of untreated sewage into the Orwell might turn out to be a factor in the decline of some species because some invertebrates had thrived on the nutrients, which found their way into the river mud.

However, the clean-up of the estuary had been a good move for wildlife in general.

“When I was younger I used to dig for bait in the Orwell and the mud beneath the surface was often black with nutrients. Too much nutrient in the mud can kill so it is always a question of finding the right balance,” he said.

Mr Wright believes that loss of inter-tidal, the impact of dredging and erosion from “shipwash” are likely to be more responsible for the decline in bird species but more research was needed.

FagburyFlats, an area of mudflat colonised by Felixstowe Port, had never been replaced while dredging the shipping channels and the wash from ship movements were potential causes of habitat erosion.

Julian Roughton, wildlife trust director, said the halt to discharges of untreated sewage had been a “huge step forward” for the Orwell Estuary environment.

“It has brought a better and cleaner habitat for a wider range of species but it may be that populations of certain invertebrates have declined as the result of lower levels of nutrients,” he said.

However, loss of estuarine nutrients was unlikely to be the only factor in the decline in water birds.

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