Acro from hell

“Turkey is a European country, an Asian country, a Middle Eastern country, Balkan country, Caucasian country, neighbour to Africa, Black Sea country, Caspian Sea, all these.” – Ahmet Davutoglu, Turkish Ministry for Foreign Affairs

After almost 2 weeks with easterly winds and both an Eastern Subalpine Warbler and a Spanish Sparrow already in the ringing season summary, it’s worth to pay attention to every bird we catch in order not to miss any of the more cryptic taxa. This practice proved to be useful with Siberian Chiffchaff but some other species/subspecies are even harder to be pointed out. A worn Iberian chiffchaff, an eastern form of Lesser Whitethroat… If you feel asleep, you’ll miss your chance!

Today’s bird was a cold-toned Acrocephalus warbler. My first thought (keeping in mind one had just been ringed at Gedser, Dk) was a Blyth’s Reed Warbler, but a quick look revealed the darkish centres of the tertials, the non-emarginated p4 and, moreover, flight feathers were too fresh, reminding more of a Marsh Warbler -I would expect them to be worner in a spring Blyth’s due to different moult timing-.

acrocephalus-scirpaceus
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.

However, the overall coloration was strikingly cold, with grey-olive edges in both greater coverts and tertials, a paler rump and mantle and a greyer nape and crown. The pictures below show the mantle and the edges of both tertials and GCs of a normal Reed Warbler (in the left) and the cold-toned bird (in the right). The difference is quite remarkable.

gc-edges
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.
upperparts
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.

With a wing-length of 66, our next thought was a VERY small Marsh Warbler. The primary’ wear fits with this species and the overall coloration (despite arguably greyer in this bird) could be closer to Marsh rather than to Reed. But the structure of the bird was not that of a Marsh Warbler. The head looked big in relation with the rest of the body and the bill was long, with the typical shape of a Reed Warbler. The notch in p2 (as shown in the photo of the primaries below) was also too long for Marsh and the nails were almost as dark as in a Reed. This comparison shows today’s bird (in the top) and a Marsh Warbler (in the bottom). Note not only the shape of the bill but the shape of the nostrils, being more rounded in Marsh.

bill-comparison-marsh-reed-warblers
Eurasian Reed Warbler Acrocephalus scirpaceus (top) and Marsh Warbler Acrocephalus palustris (bottom). Falsterbo, Sweden, June 2013.

The next plausible explanation was the bird being a Caspian Reed Warbler A. [scirpaceus] fuscus, the Asian race of Reed Warbler. Despite its still discussed taxonomic status, it’s actually a quite distinctive form, keeping in mind the big mess that these Western – Eastern forms of old-world warblers usually are. In terms of plumage wear, everything seemed to fit: to summarize, fuscus shows a Reed Warbler structure with a Marsh Warbler moult (later in the winter, not starting before December), just as our bird. The tail also showed some funny white fringing on the tips of the feathers. In my experience with Reed warblers in the Iberian Peninsula, this is not a reliable feature, at least not with this restricted amount of white.

tail-pattern-reed-warbler
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.

Moreover, the white tips of the primaries also pointed to fuscus. some fresh scirpaceus can show these white tips, but they are usually restricted to the outer web of the feather. In this bird, however, the white was in the whole tip, what includes both webs of the feather. Also, the the primaries were more square-shaped than they usually are in a Reed warbler, as described in the literature. And last but not least, the distance between p4 and p3 was really small, much smaller than in a typical Western Reed Warbler. You can see these features together with the notch in p2 (too long for a Marsh) in the pictures below.

primaries-rump
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.
notch-square-p5
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.

Unfortunately, not everything fitted with fuscus. The relative position of p2 did correspond with scirpaceus, equaling p4, whereas in fuscus it should fall between p4 and p5. It seems there is a lot of variability among the Reed warbler complex in that sense so let’s see if a fuscus can also show this aspect of the wing formula.

wing-formula
Eurasian Reed Warbler Acrocephalus scirpaceus. Falsterbo, Sweden, June 2013.

The feather samples are on its way to be analysed. In the meanwhile, and just to have fun, here it is my bet: Caspian Reed Warbler Acrocephalus [scirpaceus] fuscus.

[UPDATE: the genetic analysis revealed this bird is just a nominate scirpaceus. My conclusion here is that colouration is subjective and usually related to wear, so we should pay more attention to biometry when dealing with a tricky Acro id, especially in spring. In this case, p2 position didn’t fit fuscus and this feature isn’t subjective or wear-dependant. Thank you very much to Doc. Martin Collinson for the analysis.]

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