White Wagtail, Pendle Hill CLICK ON IMAGES FOR LIGHTBOX
WHITE WAGTAIL, PENDLE HILL, 1 MAY 2021
Looking closely at the White Wagtails (that is both subspecies White Wagtail (nominate alba) and Pied Wagtail (yarrellii)) that occur in East Lancashire quickly shows that they vary quite a lot. While the bird on the short turf just above the gate to Pendle Hill (Phil Larkin tells me ‘Pen-dle Hill’ literally means ‘Hill-hill Hill’!) on 1 May looked to have a pale mantle, pale flanks and a fairly sharply demarcated black cap so therefore a White Wagtail right? Yes, of course but I was interested to rule out an intergrade alba/yarrelli and I also remembered there can be some overlapping features, so, without being able to recall all the details, I took some photos and checked them later to Adriaens, Bosman & Els’s paper ‘White Wagtail and Pied Wagtail: a new look’ published in Dutch Birding in 2010, which is the current standard reference. It shows there is more to them than a glance at the identification features mentioned in such as the Collins Bird Guide. Here’s what I think of this bird.
Age/Sex
First of all, it is still in pre-breeding moult so it is scruffy and that ruffled black-centred (adult) greater covert means I can’t see if the outer ones are really brownish or not. The primaries are covered in all photos too. So, it could be an adult or a first summer. I’d be interested to hear from someone who looks at them regularly if there’s anything you can see here that clinches the age. The black cap looks to have a sharp border with the grey mantle, which suggests it is a male.
Subspecific Identification
Here’s an assessment using Adriaens, Bosman & Els’s eight characters. So, a White Wagtail, Motacilla alba alba, and the scores for characters A, F & G lean towards a western i.e. Icelandic bird, as expected. After all it was in good company with lots of other Iceland-bound birds in East Lancs this weekend like wheatears and whimbrels so this wouldn’t be a surprise.
Character A: Kodak grey value of rump (measured in palest parts only)
10 (between the second pair of tertials), putting it comfortably within the range of alba (western 9-14 and eastern 8-13) and outside yarrellii (13+) with some margin for error both in the lightness and artefacts in the image [The area between the third pair of tertials is the darker uppertail coverts]. This area of the rump is typically darker than the rest of the mantle/scapulars in White Wagtail (alba).
Character B: Kodak grey value of scapulars
7, within the range of alba (7-11) and outside that of yarrellii (10-18).
Character C: Kodak grey value of mantle
7, within the range of alba (7-12) and outside that of yarrellii (10-18).
Character D: Estimated amount (%) of black on mantle and scapulars
<5%. However, difficult to assess from these images, the dark-looking feathers on the mantle are sometimes ignored as artefacts but there look to be at least 3 feathers with some dark markings on the LHS of the mantle.
Characters E & F: Kodak grey value of and extent of dark wash on flanks
Kodak grey value: 7, within the range of alba (1-10) and outside that of yarrellii (9-16).
Extent of dark wash on flanks: 1 (eastern alba 17%, western alba 44%, yarrellii 37%). This is a three point scale only (0,1 & 2).
Character G: Number of dark spots on belly
Zero. As in 96% of alba. ‘The presence of several (>1) distinct, isolated dark spots on the belly seems to be a fairly good indication of yarrellii, and it is therefore surprising that this character is apparently not described anywhere in literature.’
Character H: Length of white wedge on inner web of t5
Not visible on any photos.
White Wagtail, Pendle Hill (difficult to say if the, mostly concealed, outer greater coverts or the primaries are brownish)
White Wagtail, Pendle Hill (the darker grey rump is just visible between the middle tertials)
PIED WAGTAIL, ALSTON RESERVOIRS, 1 MAY 2021
Applying the same set of criteria to a Pied-looking bird at Alston later in the morning, maybe associated with a mini fall of Greenland-type wheatears and Whinchats, it was interesting to have a closer look at it too.
Pied Wagtail, Alston Reservoirs (the brownish primaries and outer greater coverts show this is a first summer but the mantle and scapular base colour is still just within the range for alba!)
Age/Sex
The photos I managed of this one, also in pre-breeding moult, showed a definite first summer bird, with brownish primaries and outer greater coverts contrasting very clearly with the black centred new inner greater coverts. It is not possible to separate males and females with certainty in spring. Interestingly its tertial moult is asymmetric with only two new feathers, the outer ones and both in the left wing, the rest are worn and brown. I had no idea they did this, I would have guessed moult would be symmetric.
Subspecific Identification
Another patchy bird that I find difficult to assign a Kodak grey value to areas like the mantle and it’s interesting to see that White Wagtails (alba) can have quite dark mantle, scapulars and flanks, as well as the extent of the grey on the flanks. However, the most heavily pro-yarrellii features, outside the range for alba, are A&D (the almost jet-black rump, not just the uppertail coverts, plus the extent of black spotting on the mantle) and there are no features outside the range of yarrellii, so it is a Pied Wagtail. Probably wasting time looking at it as deeply as this but it was interesting to read that a very few alba and yarrellii can look more similar than you might think in spring and that’s even before we get to intergrades, that for instance can have a light mantle outside the range of pure yarrellii but a jet-black rump that rules out pure alba!
Character A: Kodak grey value of rump (measured in palest parts only)
18 (between the second pair of tertials (the first pair would usually be longer of course)), at the extreme end of the range for yarrellii and miles out of range of alba. Jet-black at the end of the scale is 19.
Character B: Kodak grey value of scapulars
11, just within the range of yarrellii (10-18) but also within that of alba (7-11).
Character C: Kodak grey value of mantle
11, just within the range of yarrelli (10-18) but also within that of alba (7-11). Adriaens, Bosman & Els’s write ‘The results may suggest a broad area of overlap around Kodak 10- 11 between yarrellii (53%) and western alba (70%)’.
Character D: Estimated amount (%) of black on mantle and scapulars
c.30%. Majority of black markings on the upper mantle decreasing towards the lower mantle. Well outside the maximum for alba (10%).
Characters E & F: Kodak grey value of and extent of dark wash on flanks
Kodak grey value: 11, just outside the range of alba (1-10) but within that of yarrellii (9-16).
Extent of dark wash on flanks: 2 (eastern alba 0% western alba 20%(!) yarrellii 60%)
Character G: Number of dark spots on belly & Character H: Length of white wedge on inner web of t5
Not visible on any photos.
Pied Wagtail, Alston Reservoirs (the dark markings in the mantle are not within range for alba. It has two new black-centred tertials in the left wing and the moult contrast in the greater coverts is very obvious with the black centred new inner feathers and the brownish outer older generation feathers. It also has less white on the forehead than typical alba)
Pied Wagtail, Alston Reservoirs (an almost jet-black rump is visible ruling out alba. The dark grey wash on the flanks is probably just outside the range of alba but the extent of it is still just within)