Wednesday, 14 October 2009

Nomadic ibis visits Norfolk

The Tas and Yare valleys contain some of Norfolk’s less accessible stretches of river and riverside marshy ground. The degree of isolation – the rivers passing through areas of privately owned land and lacking public rights of way – has made it difficult for local birdwatchers to catch up with one of our more engaging visitors of the autumn, the Glossy Ibis. Over the last few weeks several of these birds have appeared in the county, seemingly favouring the marshy ground to the south of Norwich. They are part of a much larger arrival of these rather odd looking birds, which are more usually encountered in parts of southern Europe and Africa.

The arrival stems from the nomadic behaviour that is seen after the end of the breeding season, with young birds in particular prone to wander over large distances. The species itself has a very wide global distribution but breeding populations within Europe have been, until recently, rather small. That in southeast Europe has been in decline, perhaps reflecting the degradation of favoured wetland habitats, but this is in contrast to the expanding population now established in southern Spain. It is likely that the individuals seen in Norfolk over recent weeks have come from the Spanish breeding colonies, even though this population has traditionally been largely resident rather than migratory (as happens with certain populations elsewhere).

With a strongly down-curved bill, the Glossy Ibis has been described as looking like a cross between a Curlew and a heron. The deep maroon plumage, which can appear black in poor light, contains brighter areas of green or purple sheen and a breeding adult is a particularly attractive bird. It is similar in size to the now familiar Little Egret and noticeably smaller than a Grey Heron, with a distinctive silhouette when seen in flight. Small groups of Glossy Ibis often adopt the habit of flying in a trailing line. Habitat-wise, the species prefers to feed in shallow water, typically the marshy margins of inland lakes and rivers. Here it will feed on various insects, crustaceans, molluscs, amphibians and, occasionally, fish. The diet seems to reflect what is available in the locality and it also varies with season. It is less often encountered on coastal marshes. The feeding areas are often some distance removed from those sites used for roosting and this provides an opportunity for the birdwatcher to pick up the ibis as it flies between the two in early morning or late afternoon.

Catching up with this bird in Norfolk is not easy, even in an autumn with an influx as large as this one, but you never know. Keep your eyes peeled, especially if on the train from Norwich to Lowestoft or Yarmouth.

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