Thursday, 11 January 2007

Watch out for wild duck

At this time of the year, the disused gravel workings that punctuate the Norfolk countryside are often home to wild duck. Some of these duck will have travelled only a short distance, from breeding sites here in the UK, but others will have arrived from as far away as Russia and Eastern Europe.

The string of flooded gravel workings that sit alongside the Little Ouse to the south of Thetford support small numbers of wintering duck and I often visit them to see what has dropped in. Wild duck are nervous in the presence of humans and so tend to choose those pits that are less disturbed by fishermen and walkers. Just the other day, for instance, there was a flock of thirty or so tufted duck on the most remote of the pits. The striking males, with their blue-black and white plumage, golden eyes and floppy top-knots are instantly recognisable; although the females, more demure in their appearance, can be confused with a number of other species. ‘Tufties’, as they are known, are the most widespread and numerous of our diving ducks. Our small but increasing breeding population has benefited from the spread of gravel workings, with pairs tending to nest on small islands, safe from most predators. Although not something that I have tested, the tufted duck has a reputation of being unpalatable and this may be one of the reasons why it has shown an increase in its breeding population and long-term stability in its wintering numbers.

The adults dive in search of food, favouring a range of invertebrates, especially snails and zebra mussels. The zebra mussel is a recent introduction, first reported from the London docks in 1824, since which time it has spread to many other waterways. Adult male tufties leave the breeding grounds in late June or early July and move to a small number of our larger reservoirs, most notably Abberton Reservoir in Essex, to undergo moult. This behaviour is a form of ‘moult migration’, something that is more pronounced in certain other species, for example shelduck and Canada goose. The arrival of winter sees the tufties on their wintering grounds. Vast numbers winter in the Baltic and on Lake IJsselmeer in the Netherlands and these flocks dwarf the numbers wintering here in Norfolk.

Another duck that may be encountered on the disused gravel workings during winter is the goosander. A member of the sawbill family, so named for the tiny backward facing teeth that line the bill, the goosander feeds on fish – much to the annoyance of sporting fishermen. This long-necked bird has a flat-backed body and sits low in the water, its body shape ideal for underwater pursuit of its prey.

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