Saturday, 28 May 2011

Bristol Waterfowl 4: Shelducks


A common sight on wetlands in the Old World, from northern Europe across as far as New Zealand, are the various species of large, colourful ducks generally referred to as shelducks. They tend to prefer water in the middle of open country, or on the coast, and their diet tends to be biased towards aquatic invertebrates, although some plant material is also taken.

Common Shelduck
Shelducks are not especially gregarious, and tend to be seen singly or in pairs in large flocks of other species, but when moulting they may gather in large groups at traditional lakes or estuaries.

Shelducks tend to nest in holes or tree hollows, and in Britain and much of the rest of Europe they often use rabbit burrows. They will also take to nest boxes of a suitable size, especially if they have an entrance tunnel. The clutch is 6-12 eggs, and both parents look after the young.
Ruddy Shelduck
Crested Shelduck

Most species of shelduck have stable or increasing populations, so they are listed by the IUCN as of Least Concern. One species however, the Crested Shelduck, is either extremely rare or possibly extinct (no confirmed sightings since 1964). If the Crested Shelduck survives, it will be as a very small population in north east China or North Korea, so going looking for it may be a bit risky for even the most intrepid birder.

In Europe two species of shelduck are found, the Common Shelduck Tadorna tadorna, and the Ruddy Shelduck T. ferruginea. Common Shelducks are mostly coastal birds, whereas Ruddy Shelducks tend to frequent saline lakes inland, and have a range extending further east into Central Asia and India. There are some records of Ruddy Shelduck from previous glacial and interglacial periods in the UK, and they also turn up as vagrants from Eastern Europe, causing much anguish amongst birders as they try to decide if they are genuine vagrants or escapes (various shelduck species are common in waterfowl collections).

At present, Bristol has 3 shelducks in the collection. However, they may confuse people as to their correct identification, as they are hybrids of Ruddy and Common Shelducks. Originally we had both the parent species, and eggs from a female Ruddy Shelduck were raised believing they were purebred birds, as the ducklings of Ruddy and Common Shelduck are extremely similar. As they matured it became plain that they were a mixture, so they are just display birds now and are not bred from. Oddly, they seem in many ways to resemble the Cape Shelduck T. cana of South Africa. For hybrids to resemble a completely different species to either of the parents is not uncommon in waterfowl, which as a group are prone to hybridise in both captivity and the wild.
Cape Shelduck

Next week: how a 7th century saint instituted one of the world’s earliest bird protection laws – and how the beneficiaries became the foundation of a multi-million dollar business.

(images from wikipedia)

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