Thursday, February 8, 2024

White Wagtail mystery

In May-June 2019 (pre-covid, pre-war, another era) I led a Rockjumper tour to Uzbekistan and Kazakhstan (read the tour report here). Our first morning session was spent in the mountains above Tashkent. We drove up to Hotel Beldersay and birded the forested slopes above the hotel. It was a brilliant morning, the scenery was stunning with the backdrop of snow-capped mountains and lush valleys. 

Birding was exciting, as expected for a first morning in a new destination, in fact a whirlwind of new and beautiful birds. Our excellent local guide Timur and I worked hard, picking up new birds continuously and showing them to our clients. Highlights from that morning included White-winged Woodpecker, White-capped Bunting, Yellow-breasted (Azure) and Turkestan (Great) Tit, and a flyover Red-footed or Amur Falcon - both would be rarities for Uzbekistan. Check my eBird checklist here

Because I enjoy studying geographical variation of familiar birds, I was facinated by golzii Common Nightingale and althaea Lesser Whitethroat. I also paid attention to White Wagtails up there. There were several wagtails in the hotel gardens, busy in breeding activity including song and display. Several individuals looked like typical Masked Wagtails - Motacilla alba personata, with a pale grey mantle, and a clear-cut contrast between the black nape and grey mantle. I like Masked Wagtails very much as they are a distinct taxon that is a rare vagrant to Israel, most recently in February 2023.

Masked Wagtail Motacilla alba personata, Hotel Beldersay, Uzbekistan, 17 May 2019

Other wagtails up there were distinctly different. They had very dark, almost black backs. In fact, the upper back was concolorous with the black nape, lacking the clear contrast of personata. There seems to be some variation between the individuals I saw, perhaps individual variation or related to different light conditions or photo/editing artefacts. Yet this dark mantle, lacking contrast or unclear contrast, is consistent and apparent in all the photos I kept.

White Wagtail ssp. Motacilla alba ssp., Hotel Beldersay, Uzbekistan, 17 May 2019

Anyone who has led tours knows how intense the work is. Indeed, I was very busy that morning and eBirded in haste, entering a wrong subspecies for these strange wagtails - Black-backed. Of course had I looked up White Wagtails subspecies properly this mistake would have been prevented, but I didn't. My bad.

Fast forward to yesterday, I received an email from eBird, rightly questioning my observation of White Wagtail (Black-backed). Clearly the subspecies I noted was incorrect, so I edited the checklist and for the time being I left these wagtails without a subspecies. This is where it's getting interesting. Today I did look at different White Wagtail taxa and their ranges. Curiously, alboides - 'Hodgson's' White Wagtail, looks superficially similar to the Uzbekistan birds I photographed, but its mantle is proper black all the way down, unlike the birds I saw in Uzbekistan that had dark grey backs. Or is it? Looking at alboides images on eBird, most have proper black backs, like this one, while quite a few birds have dark grey backs, not dissimilar to the birds I photographed, like this one. Looking at this gallery, surely there is some confusion in separation between personata and alboides, especially on their wintering grounds.

I found on eBird another image of a dark-mantled bird from Hotel Beldersay, a few days before I visited there - possibly one of the individuals I had:

Maybe this one also is dark-backed, from Tashkent City, but the light conditions are harsh and there might be some contrast between nape and mantle:

According to Birds of the World, alboides is 'Partly resident in southern China and northern Laos, west to northern Myanmar and northeastern Pakistan'. The eBird map looks like this:

The map above of White Wagtail subspecies distributions was extracted from a cool article based on a study by Semenov et al. (2018). The bottom line of the study (if I understand correctly) is that despite very little genetic variation, different White Wagtail subspecies show highly distinctive morphologies. What is relevant for me, at this moment, is the 'holistic' range map of different taxa, which apparently overlaps with the eBird map (based on actual observations). Both range maps don't show an extension of alboides into Uzbekistan. However, compared to other parts of the world, that region of Central Asia between Pakistan and Uzbekistan is somewhat understudied. I can imagine an extension of alboides northwest through Tajikistan towards Uzbekistan that went undetected. Certainly, Tajikistan is an under-birded country. Looking through White Wagtail photos on eBird from Tajikistan, I couldn't find any photos that clearly show dark-backed individuals. 

It is interesting that I saw two distinctively different plumages of White Wagtails breeding at the same location. I present here a very hypothetical speculation: Perhaps, if personata and alboides do get in contact somewhere in that region, birds produced from that mix could look like the birds I photographed? This could explain the intermediate mantle pattern. Or perhaps there is an east-west cline from black-backed alboides in the east to pale-backed personata in the west, and everything in between? Surely, deeper study needs to be conducted to understand what is happening here - my speculations are totally tentative, based on nothing. Proper documentation across the proposed contact zone, DNA material collection and analysis are some directions to be explored. In any case, using the late Martin Garner's phrase, always learning! I am very happy to learn from people with more experience than me and different insights - looking forward to hearing from you.

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