Tuesday 11 November 2014

White Wagtail -presumed lugens x leucopsis hybrids

I'd hoped to spend some time checking out autumn plumages of White Wagtail Motacilla alba lugens (Black-backed Wagtail) last month. In the event I only managed two visits to the fields at Ogura and though Wagtails were very common on both it was only on the second occasion I found a tractor attracting a large concentration intent on following the plough rather than my presence.

White Wagtail is a common, even very common, bird in Kansai, there are impressive numbers on the fields in spring and autumn in particular and very large urban pre-roost flights can be seen in some places. As yet I've never seen M. a. leucopsis (Amur Wagtail) despite them being a casual breeder, mainly in western Japan, and quite easy to find in winter from Kyushu southwards.

Nevertheless it's clearly possible to find apparent hybrids in the Kyoto area and I was delighted to find two such birds following the plough last month. Neither of these were as obvious as a male I first came across a few Octobers ago (while waiting at a bus stop of all places) and presumed hybrids like these recent two would almost certainly be overlooked unless someone were actually paying close attention to the White Wagtails. Two birds in a flock of about 50 Wagtails begs the questions how common might they be and where they might be coming from at this time of year.

All these birds look very white faced recalling leucopsis but show traces of a dark eyestripe behind the eye and a dark border to the rear ear coverts which that taxon would never have in any plumage. The following bird is the first individual I saw and is the most eye-catching of the three shown in this post.

This bird which happened to share the same bus stop as me on 29-30 October 2008 (it may have been there longer but I wasn't) appears to be an adult male lugens x leucopsis hybrid. The extent of black up the rump and black spotting on the mantle and scapulars suggest it's male. The white face is typical of leucopsis and white wing coverts of adult lugens. Not found on any potential taxa here and seeming indicative of hybrid origin is the slight rear eyestripe and narrow border to the rear of the ear coverts which in turn has a white surround isolating the ear coverts, not unlike the pale surround of first winter Citrine Wagtail. 

Coming to the two individuals last month, I wasn't able to get many useful shots of the first bird as it was a little distant and the first three images are the best I could manage but the second allowed better views.

I have no confidence regarding the age or sex these birds but if pushed I'd opt for adult female, particularly for the first of them. I don't see any need to look beyond the leucopsis x lugens combination to explain the appearance of these birds but the occurrance some of non-breeding baicalensis (Baikal Wagtail) could well go unnoticed away from migration hotspots and where lugens is common.

Bird 1: The combination of dark primaries because of very narrow white fringes and clearly visible grey bases to the secondaries is odd in view of the white adult-looking median and greater coverts. The mottled, dirty-looking rear ear coverts link the nape to breast on this bird.

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