REMARKABLE CHIFFCHAFF IN CASTRICUM IN 2009 (2017)
- Short note: remarkably coloured chiffchaff trapped in Castricum in 2009
- Is it an Iberian Chiffchaff, or not?
Figure 1. The mysterious chiffchaff at Castricum, Noord-Holland, 27 September 2009. Note the bright colours (Arnold Wijker)
On 27 September 2009 an interesting chiffchaff sensu lato was trapped in Castricum, Noord-Holland, the Netherlands. The bird had greenish upperparts and conspicious yellow tones on the supercilium and undertail coverts: a chiffchaff with juvenile Willow Warbler (Phylloscopus trochilus) colours so to speak.
Naturally the keen ringers in Castricum wondered if this could be an Iberian Chiffchaff (Ph. ibericus). At the time feather samples were only collected in Meijendel, so there’s no DNA-analyses. And it did not call. The rarity committee rejected the record.
Two articles in the August 2017 issue of British Birds deal with moult and primary spacing in Iberian Chiffchaff. This renewed my interest in this bird. This is what I came up with.
The combination of a largely yellow supercilium, yellow undertail coverts and greenish upperparts are striking. Though highly variable, this bird is much more intensely coloured than the average Common Chiffchaff (Ph. collybita) in autumn. If I ever trap a bird like this, I'll surely get excited! The plumage is quite similar to this Iberian from Portugal:
Figure 2-3. Iberian Chiffchaff, head and untertail coverts, Charito, Portugal, August 2017 (Thijs Valkenburg)
However, a second look reveals both plumage and structural features that bother me.
First of all, the legs are blackish, and the soles are yellow: typical for Common (Figure 4). In Iberian I prefer to see that hard-to-define orange brownish colour, especially on the rear side (Figure 5).
Figure 4. Note the blackish leg colour, typical for Common Chiffchaff, Castricum, Noord-Holland, 27 September 2009 (Arnold Wijker)
Figure 5. Typical leg colouration of Common Chiffchaff (left) and Iberian Chiffchaff
Second of all, the primary projection* seems to be too short. In Iberian this is roughly 70% (meaning: when the length of all three tertials is set at 100%, the length of the visible primaries of the folded wing is 70% of the length of the tertials). In Common this is roughly 50-60%. In this bird I measured 57% and 56% respectively. Hence: good for Common, but apparently too short for Iberian (Figure 6).
Finally, in Iberian the 5th primary (ascendantly numbered; meaning that the outer primary is p1) is usually shorter than p4. This means that p4 forms the tip of the wing in Iberian. In this bird p4 and p5 are of the same length, as in Common. This was measured by Arnold in the field, but it is also visible on the pics (Figure 6). Note that this is somewhat variable in Iberian and therefore not diagnostic, but it is something that I prefer to see in a silent vagrant!
Figure 6. Relatively short primary projection (55-60%) far less than the desired 70% for Iberian. Castricum, Noord-Holland, 27 September 2009 (Arnold Wijker)
Renewed stuff: moult
The moult pattern (Castelló Massip & Gil-Velasaco, 2017) was, as the authors write themselves, published before. The original sources were for instance summarized well by Demongin (2016). But in BB the implications are so clearly presented that they can even be used for field identification.
To cut it short: the post juvenile moult in Iberian differs diagnostically from Common. Unfortunately there are no pics of the spread wing or tail. On the available pics of the Castricum bird I can't find any moult contrasts, nor did the ringer in the field: Arnold aged it as "full grown", so as an unaged bird (not unusual, since chiffchaffs are not always easy to age in autumn). Young Iberians apparently moult a few outer primaries. In this bird the primaries all seem to be of the same generation.
Hence: I do not see any moult that points towards Iberian.
New stuff: primary spacing
This was new to me. The bottom line is that the length of the visible part of the 6th and 7th primary of the folded wing in Common and Iberian differs. In Iberian the visible part of the 6th and 7th primary is nearly equally long. In Common the visible part of the 7th primary is obviously smaller. And IMHO that's the case here (Figure 7).
Figure 8. Note the difference between the visible part of the 6th and 7th primary. In Iberian, the visible part of the 7th should be (nearly) as large as in the 6th.
The articles in BB are IMHO no reason to re-submit this bird to the rarity committee. Yes, it's an intriguing bird: I sure as hell never trapped a Chiffchaff as colourful as this one! However, several aspects of the structure do not seem to be right for Iberian and the leg colour also fits Common Chiffchaff better. Finally, no diagnostic moult patterns were found in this bird. Hence, it seems to be justified that the bird was rejected by my predecessors in the rarity committee. An odd Common Chiffchaff seems to be the most likely ID.
So what should ringers do when they trap an interesting, silent chiffchaff?
Photograph the bird in profile (and I mean: really in profile, in a straight angle), make close-ups of the closed wing, open wing and half closed wing with al primaries visible. Don't forget to tidy the bird up before you fire a shot!
Photograph the legs well
Collect a feather
Measure the wing formula. Especially P4 – P5 and P6-p7 and p7-p8 are important.
Measure the primary projection
Check the bird for moulted outer primaries
Arnold Wijker, Lars Buckx, Jasper Koster and Joost and Thijs Valkenburg are thanked for sharing their pics and information on trapped chiffchaffs.
Castelló Massip, J. & M. Gil-Velasco, 2017. Primary moult in Iberian Chiffchaff as a means of ageing and identification. British Birds 110, 476-479
Demongin, L., 2016. Identification Guide to Birds in the Hand. Beauregard-Vendon.
Duivendijk, N., 2011. Advanced Bird ID Handbook. New Holland Publlishers, London.
Slaterus, R., 2007. Iberische Tjiftjaffen in Nederland. Dutch Birding 29:2, 83-91
Gil-Velasco, M., 2017. Primary spacing as field identification criterion for Iberian Chiffchaff. British Birds 110, 480-483
* Please note that measuring primary projection is far from exact science. The tertials and primaries are not glued together, so these feathers move independently. Therefore the projection changes when the bird's posture changes. It is however possible to get a fair idea. This bird was photographed more or less in an ideal position.