Dark Blue Almost Black

“I want to be different. If everyone is wearing black, I want to be wearing blue.”

– Maria Sharapova

We all know light and colour can fool us when it comes to assess certain bird features, but it’s hard to work out to what point. This is an extreme case of what can potentially happen and I find it very interesting especially from a rarities committee point of view. These days people -me included- only add photos to their rarity submission forms and skip the description, in their belief that a picture is worth a thousand words. Although this statement remains true in most cases, when the observation is brief, a single photo can lead to the wrong conclusion, even when we see something as 100% real.

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The kid seems to be saying “it’s a Yellow Wagtail you nerd!” (taken from the Facebook group Birding Memes; sorry, I don’t know the author)

Juan Sagardia, who was spending a weekend at Cabrera Island together with some other keen Spanish birders, sent me a photo of a nice Black-headed Wagtail Motacilla flava feldegg, readily followed by another photo of a Grey-headed Wagtail Motacilla flava thunbergii with the following caption: “it’s the same bird”. Although I obviously trust him, I had to insist and asked more than twice if he was 100% sure. Yes. Apparently there’s no way it can be a different bird and the photos haven’t been edited either. They are included here just as they came out of Juan’s camera.

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Figure 1. 2cy male Yellow Wagtail Motacilla flava. It looks almost like a perfect Black-headed Wagtail Motacilla flava feldegg here. Well contrasted black nape, straight bill and lack of dark spots on breast-sides. Juan Sagardía, Cabrera, Balearic Islands, May 2019.
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Figure 2. 2cy male Yellow Wagtail Motacilla flava. Same bird as above, which has intriguingly turned into a perfect Grey-headed Wagtail Motacilla flava thunbergii. The bluish nape, crown and even cheeks are obvious here. Juan Sagardía, Cabrera, Balearic Islands, May 2019.

I had already experienced things like that with this pair of taxa, but it had always involved poorer photos, more distant and usually with challenging light conditions such as backlit or a very strong midday sun. This time, however, the photos are more than good. Although there’s clearly some variation – note for instance the saturation of the surrounding landscape- it’s reasonable to assess the light in all the pictures as neutral or at least comparable. Seemingly, it wasn’t the case in the field: the nape looked solid black when the sun went out, but revealed itself as bluish grey when obscured by clouds. In my opinion, this bird would have gone identified as Black-headed in a standard Mediterranean spring sunny day and we would all have agreed. But is it not? Let’s look at some other features.

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Figure 3. 2cy male Yellow Wagtail Motacilla flava. Still the same bird as above. A somewhat intermediate picture. The face looks darker and the nape-back transition is now much sharper. Juan Sagardía, Cabrera, Balearic Islands, May 2019.
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Figure 4. 2cy male Yellow Wagtail Motacilla flava. Looking like a Black-headed Wagtail again. Admittedly the back could be brighter green, but I’d had identified it as such with this sole photo. Juan Sagardía, Cabrera, Balearic Islands, May 2019.

The bill looks straight, without the upward curve of Grey-headed, but, in the other hand, the green back is dark and not particularly bright, something that stays true in all the photos with their different light conditions. In Figure 6 it seems to show some dark spots on breast-sides, but they are only visible in this funny position and smaller than I’d expect in a 2cy Grey-headed.

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Figure 5. Bill shape comparison between Grey-headed (left; Lanzarote, May 2018, Juan Sagardía), mystery bird (middle; Cabrera, May 2019, Juan Sagardía) and Black-headed (right; Israel, March 2008, Fernando Arce). Note the upwards bend in the Grey-headed’s lower mandible, not present in neither the mystery bird nor the Black-headed.

Despite the high quality of the photos, everything seems to be misleading and highly dependent on light and position, what calls for caution and therefore should prevent any rarities committee from accepting this bird as anything in a vagrant context. Although it’s an easy species to photograph and its sub-specific identification is one of the oldest id debates among birders, some taxa is still poorly-documented in breeding grounds and most information is based on migrants in classical migration hotspots around Southern Europe. With the rise of the Eastern Yellow Wagtail Motacila tschutschensis taxa as potential vagrants to WP shores, it’s worth to leave some room for the classics and Black-headed Wagtail deserves to stay high up in any bird-finder’s wish-list. After that many years there, some rarities committees -and now I’m talking about the ones I’m part of- still don’t know where to place such intriguing individuals.

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Figure 6. 2cy male Yellow Wagtail Motacilla flava. Same bird again. I don’t even know how to describe the nape colour here. Juan Sagardía, Cabrera, Balearic Islands, May 2019.

**Update: There are some sound recordings!

After having read the post, Miguel Rodríguez kindly provided high quality recordings of the bird. You can hear it though his eBird list (check the variety of migrants at Cabrera island these days too…) and I’ve made a useful comparison with some recordings in Xeno-canto. The call clearly matches that of classical Grey-headed Wagtails and is far from showing the diagnostic modulations on the frequency top of Black-headed. In my opinion this sorts the mystery, but urges further caution when identifying an out of range Black-headed, as is the case in the Iberian Peninsula.

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Figure 7. Comparison of the call of Grey headed Wagtail Motacilla f. thunbergii (left), the mystery bird at Cabrera (centre) and Black-headed Wagtail Motacilla f. feldegg (right). The mystery bird perfectly matches thunbergii and doesn’t show the modulations typical in feldegg. Grey-headed and Black-headed Wagtail calls have been downloaded from xeno-canto.org; reference numbers: XC432116 and X74655.

Acknowledgements

Big thanks must go to Juan Sagardia for letting me use these amazing photos. Thanks also to Fernando Arce for his Black-headed Wagtail in-hand photo. Very big thanks to Miguel Rodríguez, who managed high-quality recordings of the call and shared them with this blog.

 

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