Monday, 9 January 2006

Good numbers of wintering duck

On Thetford’s southern edge, squeezed between Barnham Cross Common and Shadwell Stud, lies the Nunnery Lakes Reserve; a series of flooded gravel pits. The lakes are very handy, just a ten minute walk from home, and I visit them throughout the year. An early New Year visit is usually productive, with a good chance of seeing the goosanders that use the reserve as a regular wintering site. Just now there are seventeen of these fish-eating ducks on one of the larger lakes.

The goosander is the largest of the sawbills, so-called because of the serrated inner edge to their bills that helps them grasp the small fish on which they feed. With a relatively long neck and a flat-backed body, the goosander is well-adapted to catching fish. When searching for prey, a goosander will swim along with the head and neck held underwater, scanning for shoals of small fish, before diving and pursuing its prey. It is this dependence on small fish that has brought this elegant piscivore into conflict with game-fishing interests. In some areas, goosanders are shot under licence to reduce their perceived impact on certain fisheries. However, the degree to which the control measures benefit the fisheries is unclear, as is the impact on the wider goosander population.

Although goosanders breed across much of Northern Britain, they do not breed in Norfolk. Wintering numbers in the county tend to peak between mid-December and late February, making the goosander one of the latest winter visitors to arrive. The birds almost invariably winter on inland waterbodies and a number of Norfolk’s inland lakes, rivers and broads will hold one or two individuals in most winters. Only UEA Broad, the Nunnery Lakes and the Great Ouse relief channel regularly support more than a dozen individuals. While most of the British wintering population is drawn from the British breeding population, those birds wintering in Norfolk are thought to originate from the Fennoscandian and Russian breeding populations. 

One of the most interesting aspects of their annual cycle is the pattern of movements made by the males. Once the females begin incubating their eggs, males from across much of the European breeding range migrate to northern Norway, where they gather to moult in huge numbers. This moult takes several weeks and the birds do not return south until November. The females, faced with the business of rearing their young, remain on the breeding grounds to moult once the young become independent. The two sexes then meet up again at the chosen wintering sites. The good numbers present this year may be boosted later into the winter, especially if birds wintering on the Continent are pushed further west by another spell of very cold weather.

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