Thursday, 18 April 2013

Dark Legged Willow Warbler

First many thanks to anyone who is still looking at this blog - it's been a long time since my last posting.

I thought for my first real post of the resurrected blog I’d talk a little about willow warblers and chiffchaff identification – oh joy did I hear you say!.
I, like many others, have a simple way of deciding whether it is a chiffchaff or willow warbler – I look for the leg colour. I know there are other features that help distinguish them but leg colour in general is the easiest to see and hence the most relied on criteria.
Whilst out yesterday I noticed what, from first appearance, looked to be a willow moving through the scrub. It had a very strong supercillium and eye stripe and there was no flicking of the tail. I was happily clicking away and was checking that I had the expose correct when I saw that the beastie had dark legs. I followed the bird for some time and got as many shot as possible to help with the id.
The following is a result of checking my field guides, talking to Ian Hodgson at SBBO and a bit of internet research.
As I see it the key features are:
Chiff                                                                         Willow warbler
Subdued eye stripe and supercilium                 Strong(er) eye stripe and supercillium
Dark ear coverts                                                    Pale ear coverts with darker surround
Short winged                                                           Long winged
Short primary projection  (~1/2 tertials)          Longer primary projection (~ equal to tertials)
Legs generally dark                                                Legs generally pale
What follows are a series of pictures of birds that I’m sure I have  identified correctly (mainly because they called) and that show some or even most of the above characteristics though some of the key features are not very convincing. One problem with the comparison is that I have very few willow shots from spring, most are autumn birds. Still here goes.
Chiffchaff
4082 Winter chiff taken at Dungeness. Subdued super and eye stripe, legs not particularly dark (certainly not black), darkish ear coverts, wings look short and the primary projection is clearly short.


5099 Spring bird (march). Subdued super and eye stripe, legs medium coloured (again certainly not black), plain face/darkish ear coverts,  wings don’t look that short to me but the primary projection (just about seen) is short.


1992 Spring bird. Subdued eye stripe and super, legs look dark but it was a dull day, plain face though ear coverts quite pale compared to many, wings don’t look that short but the primary projection is clearly short


7233. Autumn bird. Very subdued super and eye stripe, dark grey legs, plain dark face/ear coverts, short primary projection
 

Willow Warbler
5037 Autumn bird. A distinctly yellow bird, strong supercillium but eye stripe but not that strong, pale legs, clearly pale ear coverts (pale patch beneath the eye),  can’t say much about the wing length and primary projection.


1274 Autumn bird. Distinctly yellow, strong supercillium plus eye stripe(not that strong), can’t see the legs and ear coverts don’t look that pale. The wings do look long and the long primary projection is clear.


1343 Autumn bird. Distinctly yellow, strong supercillium and eye stripe, legs clearly pale, face looks pale as do ear coverts, wing length looks quite long but primary projection is not that clear (to me anyway).
 



Now onto yesterday’s bird:
 

4048

In all bar one this bird shows all the classic willow warbler features.
In the field looked decidedly yellow (though this doesn’t show well in the pictures; Canon auto -white balance not being up to the task)
It had a very bold supercillium and eye stripe.
It has pale ear coverts with a slightly darker surround giving it a pale face.
The wings look long and has a long primary projection, the projection being nearly equal to the length of the tertials(best seen in 4048).
BUT the legs by any normal standards look dark.
I sent the picture to Ian Hodgson of SBBO and despite the dark legs Ian confirmed this is indeed a willow warbler. If you actually Google “dark legged willow warbler” you will find a host of reports where this has been seen, so whilst uncommon they are well known.
So if you think the best way of telling a willow for a chiff is to look at the leg colour beware.

3 comments:

  1. Welcome back Steve an interesting and thought provoking first effort. Maybe I and others now stand corrected ?

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    Replies

    1. Mike, Here's what I got back from Ian:

      Hi Steve

      You are spot on - it is a Willow, although it's quite unusual to see one with legs that are so dark (though they are not black). The clinching feature, apart from the the somewhat subjective structural ones like a heavier-looking bill than Chiff, is the extension of the primaries beyond the exposed tertials. The length of the feathering from the greater covert tips to the tips of the tertials it is more or less comparable to the length of the exposed primaries - in Chiffchaff the primaries would look about half that relative length. This feature is also crucial in clinching Melodious from Icterine - Melodious has shorter projecting primaries while Icterine's are longer, like Willow to Chiff.

      From an ID point of view they are excellent photos.

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  2. Nice to see you back with the blog Steve.

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