Just a quick note. I won’t normally do this for new team member posts! Already some great posts. Yet again this one epitomizes what we are about. It’s new material, not fully tested, invited you to share in the process of discovery. In the UK I don’t recall any attempt to assign Bluethroats to ‘form’ in the autumn. How fascinating that we might be able to do some. Perhaps the status of White- spotted and Red- spotted Bluethroats will actually prove to be quite different. Maybe some old photos will be reviewed. Enjoy the post.
New features for the autumn ID challenge
Due to the occurrence of ‘orange-spotted’ individuals, even spring Bluethroats are sometimes not that straightforward to ID to form we would like them to be (see a note in Birding World 23.7 pag 301-304 and here and here), in autumn there is a really big challenge. All ages and forms of Bluethroats undergo a body moult in late summer and in a proportion of White-spotted’s the freshly moulted ‘spot-feathers’ are partial or almost completely broadly tipped orange, forming an orange spot. After the body moult, many Red-spotted’s lack a solid red spot (presumable especially first winters). Instead, these individuals normally have the spot-area pale orange/reddish. Therefore in autumn White-spotted and Red-spotted are assumed not safely separable. e.g. in the Netherlands, where Red-spotted it is still a considered to be a national level rarity, Red-spotted has not been accepted in autumn before now (unless a caught bird has a wing-length outside the variation of cyanecula). Both forms moult the breast-feathers again in late winter to produce the more typical white- or red-spotted plumage (but see the above mentioned Birding World note etc. for presumed exceptions in White-spotted).
The issue keeps me busy for some time and during a visit in 2011 to the NHM, Tring, England, I had the opportunity to examine a series of autumn male White-spotted and Red-spotted Bluethroats. Comparing series of similar looking birds is often the best way to find subtle differences and although the sample of autumn ‘orange-spotted’ White-spotted’s and certain Red-spotted’s (on wing-length and location) was small there was a consistent difference in the pattern of the lower ‘spot’-feathers.
I do not normally like to use the name svecica for Red-spotted as there are more ‘red-spotted’ forms beside the northern nominate but these specimen below are most likely of that form.
In these autumn, presumed svecica, the red-orange is mostly or completely concentrated on the lower part of the ‘spot’, forming a reddish band which is bordered by a thin white line followed by the broader blue band.
In these autumn cyanecula, the pale orange is more or less concentrated in the centre of the ‘spot’ and diffusely bordered with the (more extensive) white surrounding. None of the autumn White-spotted’s had a reddish band as shown above.
Detail of lifted lower ‘spot’-feathers of presumed svecica. See how these feathers are well patterned with reddish base, white central band and blue tip.
In detail the lower ‘spot’-feathers of presumed cyanecula. These feathers are more or less plain, lacking the colour-bands of svecica. The first blue-tipped feathers had a completely white base which is visible at the upper end of the ‘spot’ in this picture.
This is typical ‘work in process’ but I think the orange band of a presumed Red-spotted male will be well visible in the field once a bird give itself away. I also hope to encouraged ringers to look at the (lower) ‘spot’-feathers of autumn Bluethroats as they have the extra tool of the wing-length to separate at least a part of the birds with certainty, and maybe they have already done so!
Let’s see what happens this autumn!