Wednesday, 4 March 2020

A snow bunting snow ball at Red Wharf Bay

In the last hour of daylight I arrived at Red Wharf Bay on Anglesey hoping to see a snow bunting which had been reported. Little did I know that it would prove such an educational bird.

I've seen snow bunting here previously, in fact one year I found a couple. Those birds were the typical race which occurs on the west coast, Plectrophenax nivalis insulea which breed in Iceland, Faroe Islands and Scotland and have brown rumps.

When I finally connected with today's bird I was blown a way by what a cracker it is, a real snow ball of a bird. The first thing which struck me was that it's clearly an adult male, very black and white (and note the extensive white primary base). However I didn't think much more about it, daylight was fading rapidly and I was due to give a talk to Bangor Bird Group an hour or so later so I returned to the car and ate my sandwiches.  It was whilst I was in Bangor that it was pointed out to me that the bird is of the race P.n.nivalis which breeds in Arctic Europe and Arctic North America.

However I like to confirm these things for myself so I had a look back through my photographs and did a little research. Why is it nivalis? I mean it's clearly not P. n. insulea but is it really nivalis? It has a very white rump which goes right up its back.

My first point of reference was the concise edition of Birds of the Western Palearctic (BWP). This clearly shows that adult male snow buntings of the races nivalis and insulea have black rumps in summer plumage. In fact, the only bird on that plate in that book in any plumage which has a white rump is adult male P.n.vlasowae which breeds in Arctic Asia. On the basis of BWP alone the only conclusion you could come to is that this bird is vlasowae. Don't take my word for it, have a look at page 1523 of BWP Concise edition, or better still look further down this post.

Unfortunately it's not that simple. Other guides, such as the Collins Guide, don't even mention the rump and show all ages and both sexes in flight with white rumps, which is clearly completely wrong for insulea at least. Furthermore, a paper in the journal Dutch Birding entitled Snow Bunting: sexing, ageing and subspecies says that a white rump is diagnostic of nivalis and even shows a photograph of a bird from 25th May with a white rump. Yet BWP clearly shows adult summer plumage nivalis with a black rump.

The really odd thing is the confusion surrounding the rump colour of nivalis. A white rump is categorically not diagnostic of nivalis because vlasowae has a white rump. A white rump might rule out insulae but not vlasowae. I've already twice repeated what the rump colour of a summer plumage adult male nivalis is according to BWP. To save myself from repeating it again, here it is (number 9).

Is BWP wrong? Of course not. Are all of the birders who tell you that nivalis in summer plumage has a white rump wrong? Seems unlikely. Perhaps a possibility is that full summer plumage is only attained on the breeding grounds, in which case birds in the UK with white rumps but which in all other aspects may look like summer plumage nivalis are actually in a kind of pre-summer plumage. I'm sure that somebody must know the answer....

I think the truth is that vlasowae is very poorly known and off the radar of most birders. Therefore it's probably often overlooked and anything with a white rump is considered nivalis even though BWP contradicts this. My best guess is that this bird is most likely nivalis but it does look really white to me and it wouldn't surprise me if it was vlasowae, but unfortunately we're unlikely to ever know for sure. It's a cracking bird though!

Earlier in the day I called in at Benllech Bay for a look at this stunning drake velvet scoter.

I took this photo at Red Wharf Bay before I saw the snow bunting so you know, it was a dull end to the day, so give me a break with the quality of the photos!

No comments:

Post a Comment

Popular Posts