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The Common Tern - far from CommonArticle by Steve White, Lancashire Wildlife Trust
The Sefton Coast hosts a long list of wetland bird species of international importance. Most come to flee the Arctic winter and return north in spring to breed. Common terns, however, spend the winter in West Africa and head for our coasts in late April for the breeding season.
As with many birds the name is confusing. These birds are far from common - about 13,000 pairs breed in Britain and roughly 40,000 in western Europe. Like most seabirds they are highly gregarious and usually nest in tightly packed colonies.
Common terns have a long history of breeding in our area. It is likely that they first colonised the Sefton Coast when forced off the Martin Mere in the mid-nineteenth century when its drainage was completed. For nearly a hundred years more than 300 pairs nested in the dunes between Freshfield and Ainsdale but the colony began to decline in the 1930s and was extinct by the end of the Second World War.
Problems with increasing disturbance from day-trippers and egg-collectors led the RSPB to set up the "Ainsdale Sanctuary" - and the first Rangers on the Sefton Coast - after the First World War - but to no avail.
It seems that the Ainsdale birds moved to colonise both the Ribble and Dee Estuaries during the 1940s. Both colonies are still thriving - at Shotton Steel Works on the Dee, and on Banks Marsh on the Ribble (having moved from Hesketh Marsh when it was reclaimed in 1980).
The Ribble colony grew to 500 pairs in 1990 but shrunk to about 200 in 1996, largely because the birds' salt marsh nest sites have been flooded by large spring tides in recent years.
Common terns began to nest at Seaforth Nature Reserve in 1986 in a quite different habitat - on artificial rafts put on to the lagoon by members of the local bird-ringing group. By 1996 this colony had grown to 70 pairs which, unlike on the Ribble, usually manage to rear good numbers of young.
Seaforth from May to August is the best place to watch these birds as they noisily display in front of the main bird watching hide, ferry fish to their incubating mates and chicks, and collectively fight off marauding gulls and sparrowhawks.
The numbers of locally breeding birds are swelled enormously in late July when thousands arrive from all around Britain, western Europe and Scandinavia.
This post-breeding gathering of common terns is probably the largest in Britain. In recent years counts of 2-3,000 birds (more than 1% of the western European population) have been made but more undoubtedly pass through. Terns roost on the sandbanks north of Hightown but in recent years most have been seen at Seaforth.
What precisely attracts them to this tiny corner of Liverpool Bay is not known but it is almost certainly the presence at this time of year of an abundant food supply.
Common terns feed exclusively on small fish which they catch by shallow plunge-diving beneath the surface of the sea. They feed across a wide area but favour places where physical features such as sandbanks or the training walls of the Mersey bring shoals of young herring, sprats and sand eels to the surface.
The sight of flocks of terns feeding offshore is an indicator that, despite problems, our coastal waters remain capable of supporting healthy fish stocks.
Nowadays common terns rarely penetrate beyond the mouth of the Mersey but until the mid-1980s they were a common sight even beyond Liverpool's Pier Head. One theory is that the birds used to follow shoals of small fish brought into the river on incoming tides which, when encountering the highly polluted river water, floated to the surface and provided the birds with an abundant feast.
By early September, when most young birds are fully independent and food is becoming more difficult to find, the lure of Africa takes hold and within days the terns are gone for another year.