21/12/2001
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North Uist Hooded Merganser added to Category D

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Press Release 21 December 2001

Hooded Merganser: Oban Trumisgarry Loch, North Uist 23 October to 1 November 2000

BOURC has voted to add the above record to Category D (species that would otherwise appear in Category A except that there is reasonable doubt that they have ever occurred in a natural state).

The location and timing of the finding of the bird, in favourable weather conditions and during a period with large numbers of Nearctic migrants arriving in Europe, suggested natural vagrancy. Although the bird, a female, was claimed to be a first-winter by some observers, following careful examination of photographs, video footage and descriptions, the Committee concluded that it was of undeterminable age.

The species' range and abundance in North America, and the question of captive status, were investigated thoroughly. The species is relatively rare in North America, particularly in the eastern part of its range, compared with other species of duck which have occurred in Britain from the same area (see, for example, Birding World 10: pages 73-75 (1997) which gives the following comparison of populations: Lesser Scaup 8 million, Canvasback 900,000, Redhead 800,000, and Hooded Merganser 80,000. The editors add that half the population of Hooded Mergansers is semi-resident on the west coast).

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The species is well known as being kept and bred commonly in captivity across Europe. The 1998 British Waterfowl Census listed for 1997 (the last year for which figures are available) a total of 51 keepers with 329 birds and reports that 92 females produced fertile eggs. These censuses very much underestimate the true totals of Hooded Mergansers in captivity in the UK as there is no requirement for keepers to register their birds. In The Netherlands, rather older figures, but equally indicative of the scale of the captive bird situation, are given in Dutch Birding 15: page 276 (1993) which reported that members of the Bird Keepers' Association reared 637 young Hooded Mergansers in 1989 and 1,437 in 1991, adding that the actual numbers were estimated to be two or three times higher (Paul Vassen pers. com.)

One colour-ringed escape has reached Iceland, where they are unknown in captivity. Similarly, colour-ringed birds have been seen in western Ireland and western Britain in locations and on dates which might have indicated wild origin (including one during the same period as this bird).

It is generally accepted that most Nearctic vagrants are birds in their first winter, more likely to wander off-course on their first migration than experienced adults. Regardless of age, the background of captive birds will always make record assessment difficult, even for immatures.

Against this background of relative rarity in eastern North America, the large numbers kept in captivity in Europe, and the uncertainty over the age of the bird, BOURC took the cautious view that the record should be placed in Category D. This is a holding category which allows for reconsideration at a later date in the light of further records, in Britain or in Europe, or of changes in distribution, abundance or vagrancy.