Humber havens that keep bird numbers flying high

Less than a minute’s walk from the car park, Mike Pilsworth stops and points across a seemingly infinite expanse of reedbeds.

Through the ice-blue winter sky floats a large chestnut-brown bird with a creamy head.

It is a marsh harrier, a bird of prey which a century ago had been declared extinct in Britain.

After making the slightest of recoveries after World War Two, it was by the early 1970s hanging on by a thread, with just one breeding pair in Suffolk remaining.

Since then, however, its revival has become one of the greatest triumphs of British conservation.

As the name suggests the marsh harrier’s natural habitat is wetland, and the vast areas of tidal reeds and mudflats covering so much of the borders between East and South Yorkshire and North Lincolnshire have become one of the bird’s English strongholds.

It is here that the waters drained from one-third of England converge to begin their final journey to the North Sea via the Humber.

This is now one of the UK’s top five estuaries for winter birdlife with more than 175,000 birds present from October to March.

Rivers like the Trent, the Yorkshire Ouse, Derwent, Aire and Calder drain through flat farmlands and, further east, the waters pass one of the largest industrial areas on the East Coast.

Mike Pilsworth is warden of the RSPB’s three nature reserves on the Humber, and he has seen the marsh harrier go from being a VIP rarity on the estuary to an everyday occurrence.

That week, says Mike, he has counted a total of 36 on the Humber. Normally, they migrate to spend the winter hunting over the huge swamps of sub-Saharan Africa but in the past decade more of them have tended to stay all year round.

It has become the signature species of the RSPB’s reserve at Blacktoft Sands, a few miles east of Goole at the confluence of the Ouse and Trent.

Indeed, the organisation took on the management of Blacktoft in 1973 when a pair of marsh harriers attempted to breed there, but it wasn’t until 1982 that they managed to produce young birds.

Six miles further east from Blacktoft is Read’s Island – another RSPB reserve wardened by Mike – which has been formed by the accretion of mud around the point where the River Ancholme from Lincolnshire meets the estuary to the west of Barton-on-Humber.

Marsh harriers have started nesting here too, as have avocets – the bird that is the RSPB’s emblem.

Until a few years ago the avocet colony amounted to almost 200 pairs, the fourth largest avocet colony in Britain.

But due to the Humber’s strong tidal forces Read’s Island suffered substantial erosion, which severely damaged the three saline lagoons where the nesting colony had been established.

It is estimated that over 40 per cent of the island had been scoured away by the Humber’s tides over the past decade, including some of the lagoon walls. This left them unable to retain water and resulted in the avocet colony declining to around 50 pairs.

“At one point,” says Mike, “it looked as though the island was going to disappear.

“But then in the last few years the Humber’s water channels suddenly changed and there was more accretion. Thankfully, the island seems to be building up again.”

Further work was carried out by the RSPB at a cost of nearly £50,000 to repair the lagoons, and so the avocet colony has been saved.

In autumn and winter Read’s Island’s greatest value is as an important roosting site for up to 10,000 pink-footed geese, which migrate from their breeding grounds in Spitsbergen, Iceland and Greenland to feed on the flat farmlands of Eastern England.

Read’s Island support’s the biggest concentration of the species between Scotland and the Wash.

The surrounding mudflats also provide food for spectacular flocks of waders and ducks in winter, including thousands of wigeon, teal, curlews, lapwings and golden plovers.

There is an estimated 30,000 golden plovers wintering on the Humber, and says Mike, the estuary is now the number one site for the species in the UK, holding around 10 per cent of the country’s total population.

Doing less well on this part of the Humber is the mallard duck. Although it is still a familiar site on the lakes and ponds of Yorkshire’s parks and at every riverside beauty spot, it is declining in remote habitats such as estuary roosts.

Changes in farming practices have meant that there are fewer stubble fields for mallards to feed on in winter.

Because of its isolated location Read’s Island does not have formal access.

Also, the dangers of the shifting sands and water channels around the island make it reachable only by experienced local boatmen.

However, birdwatchers are able to view the island from the A1077 road leading west from South Ferriby towards Scunthorpe.

At the RSPB’s third Humber reserve, Tetney Marshes to the south of Cleethorpes, access opportunities are better.

These 3,700 acres of coastal mudflats, salt marsh, sand dunes and saline lagoons support up to 50,000 wintering and migrating waders and wildfowl.

They include internationally important numbers of brent geese as well as wading birds like knots, grey and golden plovers and sanderlings.

Salt marshes cover about 700 acres of the reserve and Tetney has one of the largest areas of this threatened habitat on the east coast.

The marshes hold an important population of around 70 pairs of breeding redshanks and in winter they attract small numbers of what is currently Britain’s most threatened bird of prey, the hen harrier. Mike has worked in conservation most of his life and is used to seeing fluctuations in the fortunes of birds.

The appearance of hen harriers along the Humber in winter are a special event, reminiscent of how marsh harriers were greeted 40 years ago before they became a regular occurence.

Another change going on is that some wading birds like dunlins are also not as numerous as they once were, because milder winters have made them stay closer to their breeding grounds further north.

To monitor the situation, Mike and a team of volunteers are doing monthly counts on the Humber to go into a national database.

Why volunteers are needed

The RSPB want wetland bird counters to survey waders and waterfowl using the inter-tidal mudflats of the Humber Estuary. Training is given.

The estuary is counted one Sunday a month as part of the national Wetland Bird Survey (WeBS). You will need good bird identification skills and be happy to work alone.

Experience and knowledge of estuarine habitats desirable but not essential.

Period: One day a month – fixed dates, usually Sundays. Contact Harriet Billanie, Tel: 01904 613121.