CITRINE WAGTAIL CALLS
can ssp. be identified based on calls? (2019)
by Maarten Wielstra, Thijs Fijen, Rob van Bemmelen, Sam Gobin & Vincent van der Spek
Figure 1. Citrine Wagtail, adult, Teylingen, the Netherlands, 1 November 2010 (Arnold Meijer). Calls like ssp. citreola, looks like citreola?
Can the subspecies of Citrine Wagtails (Motacilla citreola) be identified based on their calls?
That’s what a Dutch team of birders is trying to find out. This is still very much work in progress, but the calls of some late autumn vagrants in western Europe seem to differ from early autumn birds. And there might be some hints in their plumages, too. In this web article we present some preliminary findings.
The Dutch don’t bother
In the Netherlands, Citrine Wagtail is an increasing, and annual spring and autumn vagrant (www.dutchavifauna.nl). These birds have not been identified to subspecific level. Adult males were all grey-backed, therefore excluding the black-backed form calcarata, so that basically leaves the remaining two ssp. werae and citreola as the realistic options. There are slight plumage differences between males of the latter two (citreola for instance shows darker flanks), but these are considered not solid enough for a certain ID away from the breeding grounds, since there's a lot of individual variation. Females are even more difficult. And immature birds? Well, don’t even bother... The differences between the two ssp. are so small that the outstanding Pipits and Wagtails (Alström & Mild, 2003) doesn’t even recognize werae as a valid subspecies! So it's no wonder that every Citrine Wagtail in the Netherlands is…well, just a Citrine Wagtail.
Figure 2. Distribution map* of Citrine Wagtail subspecies, based on a combination of Tyler & Kirwan (2019) and Alström & Mild (2003) (map: Sam Gobin)
In general werae is the westernmost breeder (largely European), citreola breeds in the northeast and east (mainly in Asia), and the more distinctive (on plumage) calcarata breeds in the southern part of the species' range (Central Asia).
*Notes on the distribution map
To the best of our knowledge, we are the firsts to show a distribution map of Citrine Wagtail subspecies (of course largely based on existing descriptions of their ranges) - and there's a reason for that. Separating ssp. is very difficult and no one knows exactly where the distribution of one taxon ends, the other one begins, and where they might coexist or intergrade. The distribution of citreola and werae especially is therefore an indication only. Especially the separation line above the Russian Tomsk region is putative.
Figure 3. Citrine Wagtail DNA-profile groups: a 'western group' comprises the currently recognised ranges of both werae and calcarata, whereas the 'eastern group' falls largely within the currently known range of citreola (from: Harris et al. 2018; used with permission)
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.
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.
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!
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!
Figure 4. A not-so-random sample of calls with, from left to right:
1 a citreola from Russia (2015-06-12, Yamalo-Nenets Autonomous Okrug, Giovanni Boano),
2 a presumed citreola from the Netherlands (2010-10-31, Warmond, Sjaak Schilperoort),
3 a presumed werae(/calcarata) from the Netherlands (2009-09-02, Warmond, Kasper Hendriks)
4 a werae from Russia (2014-07-24, Chuvash Republic, Albert Lastukhin).
We found several features in citreola calls that seem to differ from werea/calcarata. One of the most notable is the shape of the right ‘leg’ in the sonogram: more boomerang-shaped on top in citreola, more straight in werea/calcarata. Furthermore the modulations in citreola are longer and in most cases show a ‘deeper’ lowest frequency at the end of the call. The number of modulations differs: citreola has fewer than werae/calcarata. Also, citreola more often shows a steadily declining modulating part, while werae/calcarata often stays quite horizontal to descend later during the modulation. Last but not least, werae calls tend to be longer in duration compared to calcarata and citreola. A combination of several features could very well be diagnostic for citreola vs. werae/calcarata. Different populations within the subspecies probably show some variation, so further analysis of more populations is needed. This way we hope to clear out whether we can keep our promise that it's possible to identify these taxa in a vagrancy context. In addition, we'll also analyse the plumages of immature birds (e.g. museum specimens) to see if the colour of the flanks is indeed a supporting feature.
Check the images below
Figure 5. Citrine Wagtail, 1st calendar-year, Schagen, Noord-Holland, the Netherlands, 25 September 1995 (Arnoud B. van den Berg).
No sound-recording, but note fairly late date and dark flanks: citreola?
Figure 6. Citrine Wagtail, 1st calendar-year, 28 August 2008 (Menno Hornman)
Sound-recording seems to match werae/calcarata type. Note early date and palish flanks.
Figure 7. Citrine Wagtail, 1st calendar-year, 25 August 2011 (Erik Menkveld)
No sound-recording, but note early date and palish flanks: werae/calcarata type?
Figure 8. Citrine Wagtail, adult, 1 November 2010 (Vincent van der Spek)
Sound-recording seems to match citreola. Note late date and greyish flanks.
Interestingly, we found some ‘weird’ calls recorded near border areas of their respective ranges. Alström & Mild (2003) sum up a few sources that mention hybridisation. Of course these call types need to be analysed as well. Futhermore Eastern Yellow Wagtail taxa should get some attention later on, as their calls superficially resemble those of Citrine Wagtail (cf Bot et al. 2014).
In the mean time, we'll keep on working on this to see if our first impressions will stand. We'll keep you posted!
Arnoud B. van den Berg, Martijn Versluijs, Menno Hornman, Diederik Kok, Arnold Meijer and Eric Menkveld are thanked for their permission to use their photographs. Giovanni Buano, Sjaak Schilperoort, Kasper Hendriks and Albert Lastukhin shared their sound recordings. Per Alström kindly allowed us to publish figure 3 from Harris et al. (2018).
Alström, P. & K. Mild, 2003. Pipits and wagtails of Europe and Asia. Christopher Helm, London.
Bot, S., D. Groenendijk & H. van Oosten, 2014. Eastern yellow wagtails in Europe: identification and vocalisations. Dutch Birding 36: 295-311
Drovetski, S.V., A.B. Reeves, Y.A. Red'kin, I.V. Fadeev, E.A. Koblik, V.N. Sotnikov & G. Voelker, 2018. Multi-locus reassessment of a striking discord between mtDNA gene trees andtaxonomy across two congeneric species complexes. Molecular phylogenetics and evolution 120: 43-52
Harris, R. B., P. Alström, A. Ödeen, A. & A.D. Leaché, A. D., 2018. Discordance between genomic divergence and phenotypic variation in a rapidly evolving avian genus (Motacilla). Molecular phylogenetics and evolution, 120: 183-195. Article available on Research Gate
Tyler, S. & G.M. Kirwan, 2019. Citrine Wagtail (Motacilla citreola). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from on 14 April 2019).