Dunlins on the River Mersey

Dunlins are one of Britain’s most abundant small wading birds. They are found along the coast and on estuaries in winter, sometimes in their thousands, as on the River Mersey. Their winter plumage is mainly grey above and white below: the distinctive black belly, often shown in books, is their summer plumage. The flanks are usually marked black and juveniles are often browner with white “V”-shapes on their backs. They have a slightly down-curved bill which is black, as are the legs. They show a distinctive white wing-bar when flying. There is a lot of variation in size due partly to the females being larger than the males but also because the different races vary in size.

Dunlins flying with sanderling - showing their wing-stripe. © Mike Roberts

Roosting dunlins.. © Carol Cockbain

From the ringing of many dunlins, by the Merseyside Ringing Group and others, on our local estuaries and by careful observations it is known that three races of dunlins Calidris alpina visit the Mersey Estuary: -

C.a.arctica is the smallest race and breeds in Greenland. On passage River Mersey in May/June and return in August, when they move through our estuary very quickly, using the Mersey mudflats as a pit stop, and onwards down into Mauritania and West Africa.
C.a.schinzi breeds mainly in Iceland and Scotland, with smaller numbers breeding as far south as the Pennines, the Derbyshire Peak District and mid-Wales. On passage River Mersey in April/May and return July/Sept when most move onwards, down through to Portugal and Spain and others into Mauritania.
C.a.alpina is the largest race from Scandinavia and east, far into Russia. On passage River Mersey Feb/May and return early October when massive numbers winter here on the Mersey.

C a alpina in winter plumage. © Mike Roberts

C a schinzi in summer pumage. © Mike Roberts

Over the last few years the Mersey Estuary has held the largest wintering flock in the UK of race C.a. alpina, with upwards of 40,000 birds. The swirling flocks over Frodsham Score and Hale are reminiscent of large starling murmurations with the grey and white alternating with every turn of the flocks. One wonders how it is possible that they do not collide with each other. With the large numbers present on the Mersey they attract predators and peregrine falcons or merlins can regularly be seen trying to pick out a bird from the whirling flocks. In very cold weather some birds move further south. They start to depart from the Mersey in late February/March though some birds are present through to early May when they can be mixed up with other races.

Photographs of parts of some large flocks on the River Mersey.

Part of the 44,000 dunlin at Ince, which was part of the 68,000 we had in total. in Dec '15. © Shaun Hickey

From Pickerings Pasture. © Carol Cockbain

Over the River Mersey. © Mersey WeBS

In the late 1970’s local bird watchers and walkers started noticing many dead and dying birds along the shore line of the River Mersey. On several occasions over a hundred corpses of various species were collected and sent for analysis. Millions of tellins (a marine bivalve) and other small crustacens were also found dead on the shore line. Local newspapers, the radio and television publicized the incidents which claimed the lives of over 2,000 birds which were found BUT many more 1000’s must have disappeared from the tideline eaten by predators or floated out with the tide. There was a serious attempt to cover up this incident.

The main species affected was the dunlin, covering over seventy percent of the corpses found. After almost nine months the results came back from the scientists showing that the birds had died of lead poisoning. Large quantities of tri-ethyl lead had been released into the river, by a local industrial company, for many years and had been building up in the mud. As a result of this incident questions were asked in Parliament and Michael Heseltine visited Liverpool. The impetus of all this publicity brought about the start of the clean-up of the River Mersey.

The water quality of the River Mersey has now greatly improved attracting many varieties of fish: even small numbers of salmon have moved up the estuary to breed in some of the tributaries well inland.

The main foods for dunlins in the winter months are Hydrobia, Polychaeta worms, Macoma etc. Before the clean-up of the Mersey dunlins did not feed any further up river than Oglet Bay, Speke. Now, over forty years later, birds can be found feeding in small numbers even on the other side of the new Mersey Gateway Bridge.

As a nation, we are responsible for looking after our estuaries, the birds (which come from breeding grounds in many other countries) and other wildlife which have been coming here for thousands of years and hopefully will continue to do so. We trust local business interests and local councils will give more consideration than in the past to wildlife in their plans for future developments which may affect the Mersey Estuary, whilst not forgetting that our estuaries attract many visitors for walking, sailing, fishing and to see the wildlife on our estuary, fetching in important revenues to the local areas.

Rob Cockbain