DNA confirms century old classification?

Though the plumage differences are slight, apparently Buturlin's eyes didn’t deceive him when he described werae as a subspecies back in 1907. Drovetski et al. (2018) state that based on mtDNA, werae and citreola are - despite their extremely similar plumages - not each other's nearest relatives (hence, they are not 'sister taxa'). Werae appears to be closer related to  calcarata (remember that's the most distinctive race on plumage?) than either of them is to nominate citreola! A broad genetic study by Harris et al. (2018) seems to confirm this: within Citrine Wagtails, there's a closely related 'western group', that - based on the current knowledge of their distribution - includes werae and calcarata. The 'eastern group' largely matches the range of citreola. So this is all quite surprising given there looks - but maybe less so based on calls? That's what makes this extra interesting to sort out.

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Dutch action heroes

So we found clues that the calls of citreola differ from werae and calcarata, at least on sonogram. A first step to test our ideas is to quantify differences in calls of all subspecies recorded in the breeding areas. Ultimately, we hope to show that more than one ssp. reaches western Europe in a vagrancy context, and that they can be identified. Back in the days field work was for bare handed and long-bearded heroes, that made fires to scare off wild animals. The Dutch team’s main tactics are slightly different. We lean back, grab a beer and go on the internet to look for sound recordings from the breeding grounds and to check our first assumptions. Our research has only just started and progress is slow, so there is still much work to do before we draw final conclusions. But the more samples we measure from different geographical areas, the more promising it looks.

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A funny thing… or two
And the funny thing is: late autumn birds in the Netherlands seem to show calls we associate with citreola, whereas early autumn birds seem to utter calls we associate with werae. And another funny thing: late autumn birds (incl. the 1st winters) seem to show... grey flanks, just like citreola males in their breeding ranges. And the birds earlier in autumn… usually don't!  

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Staring at legs; how it started

Yes, we should have paid attention to our own WAGS (some of them pregnant), but instead we stared at the legs of sonograms. As in the yellow wagtail taxa, a sonogram of a Citrine Wagtails call consists of two parts. An uprising first part, which could be described as two (literally more or less) parallel ‘legs’ and a descending second part which in the case of Citrine Wagtails always shows modulation (so what's modulation? That’s the shaky part of the sonogram; as if you’re telling lies during a polygraph test. This gives the call its rasping sound). We now classify and measure both parts to see if different features can be linked to different populations.

The ‘right leg’ was what initially triggered the whole idea that eastern birds (citreola) called differently. Maarten got his ‘eureka-moment’ when he took a shower after he checked sonograms of all birds recorded in the Netherlands. He realized that the only two late autumn records showed ‘diverging legs’ in the first part of the call. Coincidence? He didn’t believe so. So he ran out of the shower to check his crazy idea. He started shouting things like: ‘All wintering birds from Assam and further east call like that!’ and ‘All vagrants that call like citreola have dark flanks', and 'so are silent late autumn birds!’. The other team members that joined in later took care of his madness by trying to calm him down and to form a strategy to sort this out. A team of heroes was born!