Tuesday, November 13, 2007

Fly-by Banana-bill (Gavia adamsii) id issues

I posted the comment about id of White-billed Diver Gavia adamsii because I have concerns about the id of this species in flight. Stewart responded that he's seen a couple in flight and had them accepted by BBRC and I'm not raising the issue to cast any doubt on the records of those folk (like Stewart) who clearly know what they're about. However, caution should be exercised with this species. It's worth reading what observers who have seen plenty of these birds have to say. Kenn Kaufman for example writes, "Yellow-billed Loon (G.adamsii) should be identified with extreme caution, with attention to every possible field character." Kenn then goes on to list these characters (Advanced Birding 1990). (If readers would like me to post this stuff I will scan and post on request.) More recently Blomdahl, Briefe and Holmstrom (Flight Identification of European Seabirds 2003) indicate less directly the difficulties in their descriptions of how to separate G. adamsii from G.immer, but still imply strongly I think that it's a tricky business.

My own interest is more prosaic as I like to id to species every bird that flies by if I can and I don't think I can do this with the adamsii/immer species pair on more than about 30% of birds seen. Usually this is because I get on to the birds too late or the scope is dancing about in the wind or the birds are just too far away. I don't see that many likely suspects in any case. Of the 8, I saw on Sunday, which were mostly within id range I would judge I got good enough views to id 3 with some confidence (immer). There was one bird which I saw well which might possibly have been adamsii and the other 4 I didn't see well enough - and that was a good day. (I realise I am contradicting myself here - previous post - but I've been ruminating so forgive me.)

Now maybe if I'd seen a few in the past I might change my tune but the published criteria seem to me to be difficult to observe in flight to 100% certainty of an id. I would be interested to read any field notes of in-flight observations of adamsii or even better see some sets of photos of in-flight birds of both species in winter / 1st winter plumages (taken on the same day by the same person preferably). Maybe I'm making a meal of this (I have recently had this suggested to me) but there have been a good few Banana-bills claimed this season and maybe this species is more common than we think it is in the North Sea (I don't actually believe this to be the case in most years, I hastily add). I think a bit of a discussion might be healthy - I'd welcome the opinion of anyone who has seen a few (2 or more would do) adamsii and has an opinion.

1 comment:

Boulmer Birder said...

Alastair, field notes on my blog for fly by WBD....n