White-winged gulls

By Dominic Mitchell

One of the big birding events of this winter has been the record influx of Iceland Gulls, and anyone with an interest in gull-watching will hopefully have made the most of the opportunity to study this scarce Arctic species. The closely related Kumlien's Gull has been caught up in the influx too, and there have also been reasonable numbers of Glaucous Gulls around Britain and Ireland. There's therefore no better time to get to grips with these large, and largely white-winged, species before they head north-west for the summer.

For this reason Peter Adriaens looks in more detail at the specifics of Iceland v Kumlien's Gull in the April issue, and we'll be uploading more photo resources on the Birdwatch website to supplement this in-depth photo guide. But especially for those with less experience of gull ID, this British Trust for Ornithology video on YouTube offers additional advice on the identification of Iceland and Glaucous Gulls:

A(nother) mystery gull

By Keith Vinicombe

The odd gull (second from right). Note the slate-grey upperparts, heavy dark neck streaking, the heavy bill and dark-centred tertials (despite the adult-like plumage).

I didn’t make a New Year’s resolution, but if I had it would have been to give up looking at gulls. Or to be more precise, big gulls. This is because I’ve come to the reluctant conclusion that they’re more trouble than they’re worth, as the following example will illustrate.

I came across a really odd gull on 23 January – a first for Britain no less. Well, that was my fantasy. To get my retaliation in first, it was probably just another hybrid. It was on Herriott’s Pool at Chew Valley Lake, Somerset, where hundreds of gulls come in to bathe every afternoon prior to joining the 60,000 strong roost. To all intents and purposes, it was a Lesser Black-backed Gull, except that its upperparts were very obviously a shade or two paler than the accompanying British graellsii. I managed to take a few digiscoped photos, some of which are reproduced here.

It was in fact a very distinctive bird: dark leaden grey above with a very thick and obvious white tertial crescent. What was particularly odd was that it retained very distinctive neat brown bases to the tertials, the only signs of immaturity on what was otherwise a fully adult bird. Structurally, it was very similar to a Lesser Black-back, being rather tapered in shape, but it had quite big, almost ‘woolly’ head and its bill looked consistently longer and heavier, with a stronger gonydeal angle.

The mystery gull (right). Note the thick, blunt bill with a strong gonydeal angle, the heavy and extensive head streaking, the dark upperparts and the dark-centred tertials.

The obvious answer to such an ‘intermediate’-looking bird is that it is a hybrid: probably a Herring x Lesser Black-back, or maybe even a Lesser Black-back x Yellow-legged Gull. But, if it was either of those combinations, why did it have heavy and extensive head streaking? It had a profusely and finely streaked head, with the streaks become blacker and much more lined on the sides of the neck. The streaking then spread more diffusely across the upper breast to form quite a definite hood. Having already moulted into summer plumage, virtually all our local argenteus Herring Gulls are white headed and, as the above photos show, our local Lesser Black-backs are rapidly heading the same way (and agentatus Herrings are rare around here).

In flight it showed yellow legs, pale grey under primaries and secondaries (paler than graellsii) and a very thick white trailing edge to the secondaries – thicker than Lesser Black-back– contrasting with the leaden upperwings. It also looked stockier bodied in flight.

Note the pale grey under primaries and secondaries, the very thick white trailing edge to the secondaries and the heavy neck streaking.

It reminded me of photos that I had seen of Heuglin’s Gull – in particular the more eastern taimyrensis, which may be a hybrid form between heuglini and the eastern Siberian Vega Gull L vegae. When I got home, I had a look at the Gulls in Oman website which has some excellent winter images of taimyrensis. The Chew bird looked superficially similar to some of those images, but looking at the books was a different kettle of fish – they are so bogged down in detail that you can’t see the wood for the trees.

One ray of sunshine was Hadoram Shirihai’s account of heuglini and taimyrensis in the Macmillan Birders’ Guide to European and Middle Eastern Birds. Specific points he mentioned included: the moult (Heuglin’s moults very late, with adult’s primaries often still growing into late winter); the single isolated mirror on the outer primaries (confined to P10); the well-streaked head and neck; and traces of immaturity on otherwise adult-like birds – the last three points all fitted the Chew bird!

It had a single isolated white mirror to P10, something apparently shown by Heuglin’s Gull. Note also the fresh primaries.

But I accept that the bird was probably a hybrid, just like all the others. But the problem is, even if you do get an excellent candidate, such as the Rainham Slaty-backed Gull, how do you prove to the satisfaction of a national records committee that it’s 100 per cent genetically pure? The answer is that, without a DNA sample, you can’t – and even mitochondrial DNA can’t always provide a definitive answer, not least because it only follows the female lineage.

Cackling Geese: a closer look

Richardson’s Cackling Goose Branta hutchinsii  hutchinsii (Blagdon Lake, Somerset, November 2011). Note the square head, tiny bill, dark breast and white neck collar (photo: Nigel Milbourne).

By Keith Vinicombe

On 1 November, Nigel Milbourne discovered an unringed Cackling Goose at Blagdon Lake, Somerset, feeding with feral Canada and Barnacle Geese. He identified it as a Richardson’s Cackling Goose Branta hutchinsii hutchinsii and posted some good photos of it on www.blagdonlakebirds.com. Eventually, the bird came to its senses and moved to nearby Chew Valley Lake, but it soon moved again with the Canada Geese, this time to Torr Reservoir, near Shepton Mallet, where it remains. Disappointingly, the bird information services universally dismissed it as an escape. To rewind seven years ... 

In 2004, the American Ornithologists’ Union separated the seven large forms of Canada Goose from the five small forms, which they lumped together as Cackling Goose. In 2005, this treatment was also adopted but the British Ornithologists’ Union. However, for some reason the BOU decided to rename the two species Greater Canada Goose and Lesser Canada Goose. One problem with this is that Greater Canada Goose now includes the subspecies known as Lesser Canada Goose Branta canadensis parvipes, meaning that this form should, presumably, now be known as Lesser Greater Canada Goose! Given this oxymoron, Birdwatch decided to follow the more sensible American terminology in its Birds of Britain: the Complete Checklist, and British Birds has recently done the same. Given that these geese breed entirely in North America, then we in Britain surely should defer to the AOU’s decision on terminology.

To return to the Somerset bird, there was the inevitable argument about its identity but the issue was quickly put to bed by David Sibley, respected author and illustrator of the Field Guide to the Birds of North America. He came down in favour of it being hutchinsii and, interestingly, explained that this form is actually very variable in both its breast colour and in the presence or absence of a white neck collar; he also sent a very interesting and informative photograph to prove this (for further discussion on the ID of Cackling Geese, see http://www.sibleyguides.com/2007/07/identification-of-cackling-and-canada-goose/).

Richardson’s Cackling Goose Branta hutchinsii hutchinsii (Blagdon Lake, Somerset, November 2011), here with a feral Canada Goose Branta canadensis. It was tiny, estimated to be about 10 per cent smaller than the feral Barnacle Geese it sometimes accompanied (photo: Nigel Milbourne). 

The breeding range of Richardson’s Cackling Goose extends eastwards into north-eastern Canada and includes Baffin Island. Therefore, on geographical grounds it is the subspecies most likely to occur in Britain, and the records so far support this. Greenland Barnacle Geese (and sometimes Pink-footed Geese) act as the ‘carrier species’, the initial vagrancy presumably occurring in the Arctic. This Barnacle population winters in the Hebrides, western Scotland and western Ireland, which is where the majority of Richardson’s occur. But could they also get here on their own? Given that American ducks and even Sandhill Cranes do so, then the answer must surely be ‘yes’.

Autumn 2011 was exceptional for American vagrancy (we have had 17 American birds at Chew alone), a combination of an excellent breeding season in the Arctic and some very strong westerly gales. There has been a significant arrival of at least nine Richardson’s Cackling Geese elsewhere, with four on Islay, one in Mayo, one in Donegal and three in Sligo. In addition, one turned up on the Gwent Levels on 13 November (it was still there on at least 24 December – see www.gwentbirding.blogspot.com). Like the Somerset bird it was unringed, and furthermore it turned up at the same time and place as Gwent’s second-ever Greenland White-front.

Richardson’s Cackling Geese winter in Texas and northern Mexico, but this season there have been a number of wintering records over a thousand miles away in north-eastern Canada, where they do not normally winter. There have also been abnormally high numbers of Canada and Snow Geese lingering there. As in Europe, funny things seem to have been happening with their goose movements. Andy Davis has trawled some North American websites and has come across the following recent records of hutchinsii:

Ontario
* October 27: five near Toronto.
* Early November: two Ottawa (still reported 3 December).
* December 4: eight at Point Pelee and one at Markham.
* December 11: up to five in the Constance Bay area (present for previous 10 days or more).

Nova Scotia
Early November: one (locality not specified).

New Jersey

December 2: seven in Weequahic Park, Newark.

Obviously it’s difficult to be sure about the origins of any vagrant wildfowl, but what are the chances of two unringed Richardson’s Cackling Geese turning up only 15 miles apart at a west coast locality in an exceptional autumn for American vagrancy? Add to this the fact that there has been (a) a significant arrival of the species in western Scotland and Ireland, and (b) apparently abnormal movements in north-eastern Canada and the USA, then surely we have to keep an open mind about these birds.

P.S. Examination of photographs of the Somerset bird revealed that it is a first-winter (not an adult as currently reported by the bird information services). The scapulars clearly show a contrast between the majority of adult feathers, which are square in shape and thickly tipped with buff, and a few lines of remaining juvenile feathers, which are rounded and faintly fringed with dull buff. We have also heard of further reports of unusual winter records of hutchinsii Cackling Geese in Ontario, with up to 30 in one area.