• Vincent

In many respects autumn was remarkably slow. But November turned everything upside down!

Like in spring (with an Alpine Swift), the girls from De Wulp delivered the highlight of the season (year!).

On 5 November Lizzy sent me a WhatsApp message. She asked if I knew which species was just taken into care. Despite the pics showed a wet and scruffy bird, my pulse raised and I missed a heartbeat or two. Even I was left speechless for a bit. This was an American Catharus thrush!

A new pic of a dry bird confirmed it was a Grey-cheeked Thrush (or a theoretical Bicknell’s). A new species for the Netherlands!

Despite it was in a rather poor condition, birds are in good hands at De Wulp: it recovered well. In all I saw the bird four times. They are tiny for a thrush! The size of a Common Nightingale, but with remarkably longer wings (no less than 2cm longer). On 20 November I released the now fully recovered bird at a suitable site near where it was found. It immediately disappeared into the thickets, never to be seen again.

So how did I rule out the very similar Bicknell’s? And how did I age it?

Plumage features overlap, but Bicknell’s - a split from Grey-cheeked - e.g. has a slightly more rufous tail. The cheeks should be plain. Bicknell’s is said to have more yellow on the lower mandible – which could fit this bird. However, David Sibley questions this feature. In this bird the cheek is striped, and the tail is not slightly rufous. It has the same colour as the upperparts. So that's reason nr 1) to think about Grey-cheeked rather than Bicknell’s.

The key features, however, are in the wing structure.

First of all there’s the wing chord. I measured 102 mm. Based on other sources, Rimmer et al (2001) mention:

"Wing chord of adult Bicknell's 82-100 mm (n = 415; VINS), of Gray-cheeked 93-109 mm (n = 200; Pyle 1997)."


"Majority of Gray-cheeked Thrushes have wings >95 mm in length (Ouellet 1993); 85% of Bicknell's have wings <95 mm (VINS)."

So 2) the wing chord seems to diagnostically rule out Bicknell's.

But there's more.

The longest primary is p3 (counted from outside in). In Bicknell’s this should be P4.

Finally I measured the primary projection with a ruler. In general this is ≥ 100% in Grey-cheeked and ≤ 100% in Bicknell’s. In this bird I measured c 115% (yes, they have extremely long wings). That’s even larger than the extreme for Bicknell’s (110; Lane & Jaramillo 2000).

Based on this (not ideal) pic I measure a primary projection of 111%. With a ruler I measured 115%.

So 3) the wing diagnostically confirms the ID

Ageing this bird is straight forward.

There’s more to it, but note all greater coverts are still juvenile, with a pale tip (in this species it seems to be normal that no coverts have been moulted). In adults these are plain.

Just note the funky little detail on the inner three coverts, that have a beautiful white shaft streak!

Happy Rinse, Gerjon and myself seconds before the release, Den Haag, 20 November 2018 (pic: Roland Wantia).

PS With the Alpine Swift Rinse and I added two new species to the list of birds ringed in the Netherlands in a single year. All thanks to De Wulp!

#GreycheekedThrush #GraycheekedThrush #ageing #identification

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  • Vincent

pics © Marijn van Oss & Jorrit Vlot sound © Thijs Fijen

Earlier I wrote about Siberian Chiffchaffs with common Chiffchaff calls (here). That bird (mostly) looked like a Siberian Chiffchaff, and after analyses it indeed showed Siberian mtDNA - but in the field didn't utter the characteristic


No, it called like a Common Chiffchaff!

Now the following bird, observed on Vlieland on 25 October by Thijs Fijen and his mates Marijn van Oss and Jorrit Vlot, could very well be a similarly confusing - but highly interesting - bird.

This was a field observation so no DNA was obtained, but even though the bird is half hidden, and it's pretty dark, the pics absolutely give a tristis feel. These guys are are keen on identifying difficult birds, and based on plumage it sure looked like a bonafide tristis to them.

But here are the calls the bird uttered:

(if sound app doesn't work, use this link)

Not even remotely close to a Siberian. So yet another intriguing bird!

In the mean time our DNA work on chiffchaffs continues. At the momente we're collecting our final feather samples. We now have over 800, from several countries. Peter de Knijff and myself hope to publish the Dutch mtDNA data in 2019. A full gene analyses of all tristis (to see if we get birds with mixed genes; the bird with the 'wrong' call will be super interesting to test) will take a bit longer.

Thanks for the pics and sound recording, Thijs, Marijn & Jorrit!

#birdidentification #CommonChiffchaff #SiberianChiffchaff #calls #tristis

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  • Vincent

There's a big if - but another big redpoll invasion could be in the making.

The if depends on stuff like weather conditions, and the exact turn the majority of the wandering birds in Europe will take. But it's obvious that at the moment, a higher number of birds than usual is passing through. And they are early!

The thought alone is thrilling - two large invasions in a row would be unprecedented (as far as I could find). Note there were a long 9 yrs between the biggies from 2008 and 2017!

And it's not just Mealy (and to a lesser extent Lesser), with records in the UK and Belgium (Coues's) Artic Redpoll also seems to be involved!

In January I trapped our first Arctic ever (in 91 years of ringing), so Peter, Morrison, Ed and myself were stunned to find another one in our nets on 9 November. Note this is still a (semi) rarity in the Netherlands!

Just look at that tiny bill (a feature of this taxon) compared to the Mealy's bill on the left! It's much smaller than in last January's bird.

Also notice the broad white fringes on the rectrices and tail feathers.

The pink on the breast, flanks and rump was a bit subdued (and show less well on the slightly over-exposed pics), but this is an adult male. The tail feathers could be more rounded, but are not as pointed as in immatures, the pink stretches out over a large area (breast; flanks; rump) and the fresh tertials with the broad white edges are also adult.

The faint stripe on the longest undertail covert perfectly fits Arctic - beware though that, though rarely, Mealy Redpoll sometimes shows a similar pattern (see my ID article on this subject).

Oh yes, it of course had a large white rump (2,1 cm between the tiniest specks). The white rump reaches half way the 2nd tertial. Also note the cinnamon wash, typical for (autumn) Arctic.

What a way to both start and (nearly) end a year!

#CouessArcticRedpoll #MealyRedpoll #birdidentification #birdringing

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