More on White-spotted Bluethroats
Well unknown to me. Others know full well (not least Dominic Mitchell) there is small type of White-potted Bluethroat in NW + Western France, sometimes separated as ssp. namnetum. Irishman Eugene Archer, now resident in France helpfully wrote:
Hope all is well with you and yours ?
The blog is getting better and more exciting all the time and certainly gives one the motivation to get out there and really “look” at the birds. Well done !
So, namnetum Bluethroat is pretty much restricted to W and NW France as a breeding bird with probably the bulk of the population wintering in Spain / Portugal and maybe into Morocco. See here.
Anything marked as a probable / confirmed breeder west of a line from Cherbourg and swinging in an arc south to Bordeaux and the Bay d’Arcachon is probably namnetum.
In-hand measurements seem to be, for the moment at least, the only way to distinguish these birds from other races outside of the breeding period / range. We handle a lot of Bluethroats in autumn at the ringing station here at Donges (over 900 last year, see www.acrola.fr), the vast majority namnetum but with some cyanecula at least.
One possible visual criteria for separating the two is the extent and pattern of red / black on the tail. This is an ongoing project and nothing concrete has come up so far ! However, this year we’re working on a major study of autumn Bluethroats along the Bay of Biscay in conjunction with a network of other ringing groups (www.atlanticflyway.org) and maybe something will come out of that in the near future.
In the meantime here’s some photos of namnetum ; a first-summer male (2 retained outer GCs?) apparently on territory in March 2010, and a first-summer male from another breeding site in May 2010.
Very best regards,