Although these species do not form part of the county list they are discussed in varying levels of detail below, as they seem to be the very birds about which birders speculate the most. Several of them are wildfowl currently only on Category D of the British List (species that would otherwise appear in Category A except that there is reasonable doubt that they have ever occurred in a natural state) while others have been accepted as wild birds elsewhere but our local records are considered less likely to involve wild birds. Wildfowl are particularly difficult birds to deal with in terms of their status, as various species are commonly kept in captivity but they are also capable of astonishing feats of vagrancy.
Lesser White-fronted Goose Anser erythropus
An unringed adult was at CVL from October 18th 1991 – February 15th 1992, and the same bird was at BL on December 26th 1991. It associated with the Canada Goose flock where it was joined by a 1w European White-fronted Goose on 11th January and an adult on 3rd February, both of which stayed until February 10th. This Report for 1992 mentions that the bird’s arrival coincided with that of several others in Britain and the near continent, and suggests that it might have been from the Swedish reintroduction scheme. However, no British record was accepted by BBRC as relating to a wild bird in the winter of 1991-92.
Snow Goose Anser caerulescens
A vagrant to Britain from the Nearctic with the records most likely to relate to wild birds being of wintering individuals in flocks of wild geese, mainly Greenland White-fronted, Pink-footed and Barnacle, none of which is regular as a wild visitor to Avon. Not all conform to this pattern: 17 white phase birds in Kent in March 1980 were presumably the same as 17 in the Netherlands in April where one was seen to have a blue colour ring as used on goslings in Manitoba in 1977.
Most Avon records relate to feral or escaped birds with flocks of Canada Geese. Five (three white morph and two blue morph) on Northwick Warth from June 7th to 9th and at Chittening Warth on June 12th 2001 mirrors a flock of eight (all white morph) on the Dumbles at Slimbridge, Glos., on June 12th 2011. Stable Isotope Analysis of shed feathers were collected from one of the Slimbridge birds suggests they originated in northern continental Europe, possibly The Netherlands, but not from Arctic Canada. Its claim for a place on the county list remains very tenuous.
Ruddy Shelduck Tordana ferruginea
This species is on category B of the British list as the only records fully accepted as involving wild birds occurred before 1950 (an influx of 57 birds as long ago as 1892!). Although many of the numerous more recent British records probably relate to escapes, there is a regular later summer arrival in July-August, often featuring small flocks. In 1994 there was a major influx into NW Europe involving around 350 birds including 55 in Britain in flocks of up to 12. Significant feral populations are now established around Moscow and in Switzerland while there is a regular large late summer moult gathering in the Netherlands (460 in July 2006). The Dutch birds are of unknown origin but surely they are either wild, feral or a mixture of both, and not merely escapes. It seems reasonable to assume that some late summer parties in Britain (and Avon) have the same origin as the birds in the Netherlands.
There was a regular summer arrival of unknown origin at CVL between 1987 and 2002, though this has now come to an end. In the influx year of 1994 there were up to five at Chew between June 20th and August 14th, the peak in an unbroken 16 year run of summer records at this site.
Year(s) 1987-1992 1993 1994 1996 1997-1999 2000 2001 2002
Peak at CVL 1 2 5 2 4 3 1 2
Marbled Duck Marmaronetta angustirostris
This species is on category D of the British List with no record currently accepted as having definitely involved a wild bird. It is common in captivity and some British records have involved escapes, but it seems highly likely that some wild birds do occur. This relatively scarce species breeds from Southern Spain and NW Africa to the Middle East and Central Asia. Despite population declines a recent flock of up to 4250 was found in Tunisia in October 1999. The species is migratory and nomadic, adapted to respond to droughts that occur in its breeding range. It has regularly been recorded in Northern Spain and the Camargue in Southern France as a vagrant. Most French records are in August-September with a secondary spring peak in April. This fits the pattern of British records rather well and it has been accepted as a genuine vagrant in the Netherlands.
In 1984 an adult was at CVL from August 24th to September 18th and again on October 28th (having been at Cheddar Reservoir, Somerset from 23rd September to 27th October). It reappeared at BL from December 8th to 26th.
Hooded Merganser Lophodytes cucullatus
A wary female or immature was at BG on December 21st 1996, a time when this species was not on the British List. Subsequently the species was admitted to Category A of the British List following a review of the occurrence of an immature on North Uist, Outer Hebrides, from October 23rd until November 1st 2000. The species is common in captivity across Europe. The 1998 British Waterfowl Census listed for 1997 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. Although it is still one of the least numerous wildfowl in North America, the population there has shown a marked recent increase. Coincident with this increase, several presumed vagrants have recently occurred in The Azores, Canary Islands and Iceland. Had the Avon bird occurred after the species admittance to category A it might even have been accepted (though it has since been resubmitted and was still found unacceptable by BOURC). One factor counting against it was that the presence or absence of rings could not be established.
White-headed Duck Oxyura leucocephala
Although this species has declined across the eastern part of its range the numbers in Spain have increased from a low of just 22 individuals in the 1970s to 2000 more recently – a significant conservation success. The species has a long history of winter vagrancy to northern Europe with records from Belgium, France, The Netherlands and Germany. More recently they have been appearing in France in early autumn with a September peak – presumably post-breeding dispersal from Spain. In the autumn of 2000 up to 12 were at a single site in Loire-Atlantique, just 250 miles from the English coast. 2003 saw a significant influx into southern England with about five individuals, an adult male and four juveniles. There were also records from Belgium, The Netherlands, Germany, France, Hungary and NE Spain in autumn/winter of 2003/04. Such a pattern of occurrence seems highly unlikely to involve anything but wild birds. As with all the wildfowl species in this section they are kept in captivity but they are relatively rare.
At CVL a female was present on June 9th and 19th 1985. In 1995 a second winter male was at CVL from November 11th to December 25th. Finally in 2003 a juvenile was at CVL from August 26th to September 3rd. The last two were accepted by BBRC but placed on category D. The first was not formally submitted to BBRC. The 1995 individual was presumably the one that arrived at Abberton Reservoir, Essex, on January 2nd 1995, remaining there until 4th November. After it departed from CVL it was found at Hanningfield Reservoir, Essex in January 1996 and then commuted between there and Abberton for a few months. The last was part of the influx into southern England described above. Despite good evidence that wild birds are reaching us the species is still not on the British List.
Booted Eagle Hieraaetus pinnatus
A long distance migrant that is mainly a summer visitor to southern parts of Europe. Recently small numbers have wintered in Spain. It reached Iceland in early November 1974, so is evidently able to make long sea crossings. It is very rare in captivity in Britain and just two were registered in early 2000, neither of which had been lost at the time of the sightings below.
One was watched by many admirers at CVL from February 11th to 15th 2000 and some witnessed it catching and eating a Coot during its stay. This was the bird that had first been seen as a juvenile in the Dublin area of Ireland on March 5th 1999 and wandered to Northern Ireland later that summer. It reappeared in Cornwall in October to November then went absent until refound on the Somerset levels in February 2000, shortly before it moved to CVL. Subsequent sightings in Kent in April and Orkney in June were linked to the same bird but could perhaps have been different individuals (observers of the Kent bird reported plumage differences from the long-staying bird). It showed some damage and wear in the primaries. Having seen the bird in Cornwall and at CVL I looked carefully at various Booted Eagles in Asia and Africa in the winter months and saw birds with very similar (minor) primary damage.
The bird was only admitted to category D of the British list, one of BOURC’s most controversial decisions. This was based on the ‘arrival date’ (although surely it is more likely to have arrived the previous autumn and not been found until early March), wear to the wings, supposed inability to make long sea crossings and the presence of the species in captivity.
Note
When searching for some references to try and make this section vaguely presentable I was delighted to rediscover Keith Vinicombe’s excellent chapter on Category D species in Martin Garner’s ‘Frontiers in Birding’. I have drawn quite heavily though not exclusively on that source, though any errors are my own.
John Martin (County Recorder), November 2011