On Sunday 18th April while birding in the Farley area I walked around the large clearfell there hoping to see Tree Pipit. As I left the clearfell area along the main track, I suddenly heard a fairly distant and unfamiliar song from the woodland alongside. This immediately suggested Iberian Chiffchaff to me but it did not sound exactly like any of the previous ones I had heard before and was lacking the diagnostic “wheet wheet wheet” section of the song. I waited for some time hoping or expecting it to do a more typical version but when it did not I did wonder briefly if it could something else, maybe an aberrant Pied Flycatcher song or something, but eventually as the bird approached closer I could see it was indeed a Chiffchaff sp. Over the next couple of hours it sang the same short song phrases regularly with just some very slight variation. This consisted of regular 3-4 second phrases (a characteristic of Iberian) with something to me of the tone of Iberian Chiffchaff but lacked he diagnostic “wheet wheet wheet” section which most but not all Iberian Chiffchaffs sing, though it did seem to have something of a shortened version of the rattle. Despite spending many hours observing and listening to the bird over the next week it steadfastly refused to call whereas nearby Common Chiffchaffs regularly called as soon as they stopped singing. Interestingly I have seen three previous Iberian Chiffchaffs in the U.K. and despite several hours of observation never heard any of them call and have only previously heard calls on recordings. On one occasion as the bird dropped low into the understory I heard two Siskin-like calls in quick succession but unfortunately the bird was out of sight at the time, and although lots of Siskins were present in the area I was pretty sure none were nearby at the time. I was hoping to conclusively identify it before putting news out, but as it wasn’t calling and I could only get poor photos I decided to release news of its location in the hope that someone would obtain better photos or hear it call. Fortunately Richard Lowe and Andy Butler both obtained some excellent useful images of the bird. Finally on 30th April the bird was singing quite close by while I was examining sonograms on Xeno Canto on my phone when I accidentally played the call of Iberian Chiffchaff upon which the bird immediately flew into a Scots Pine next to me and began calling excitedly from the canopy with Siskin-like calls about 1 second apart for over a minute and I managed to record this on my phone. The bird remained in the same area of woodland, a plantation of mainly mature/semi-mature Scots Pine with a few Larch, Corsican and Lodgepole Pine with an understory mainly of Birch with some Rowan and Rhododendrons, until at least 19th June.
Size & Structure:-
In size and overall appearance it closely resembled a Common Chiffchaff but with some notable differences. It often appeared more evenly proportioned lacking the comparatively large headed impression that Chiffchaffs often give. The tail also often appeared to be quite long, the overall jizz impression being somewhere between Chiffchaff and Willow Warbler. During the early part of its stay the bird appeared to have an injured right leg often holding it up and often lowering its body to rest on branches as it sang, though at one point I watched as it stood on both legs and did a weird Dipper like bobbing on a branch for a few seconds. It also had a slightly hump backed appearance at times which I suspect might have been exaggerated by the leg injury, though I have seen numerous photos of Iberian and others labelled Common Chiffchaff having a similar hump-backed appearance. All three previous birds I have seen have also shown this to some extent, below is one of my photographs of the Potteric Carr bird for example.
Later during its stay the leg injury seemed to improve and the hump-backed appearance became slightly less obvious. The primary projection was difficult to assess in the field as the bird spent most of its time up in the canopy but it did seem to be slightly longer than on most Chiffchaffs to me. Fortunately Richard Lowe kindly sent some better photographs which reveal something of the wing formula, note that P3 (and P4 counting ascendantly) is clearly longer than P5 and that P2 appears clearly longer than P8, both indicative of Iberian (see the wing formula diagrams in Demongin Identification Guide to Birds in the Hand). These differences would result in a longer primary projection. On Common Chiffchaff P3 P4 and P5 are similar in length with, if anything, p4 often appearing to be the longest on open wing shots. This gives a much more rounded tip to the wing. I don’t have any open wing shots of Common Chiffchaff but compare with these birds online in the links here, here, here and here as well as the wing formula photos here though note the primaries are numbered decendantly at this site. On 22nd May I got very good views as the bird preened in good light against a tree trunk and I could see a clear contrast between fresher darker outer and more faded/worn inner primaries. Andy Butler managed to get some sharper photos, one showing worn inner primaries on his blog, these would normally be the most protected and least worn on a Chiffchaff, see here. This moult pattern is a regular feature of second calendar year Iberian Chiffchaffs which usually moult one-six and sometimes seven outer primaries during their first winter unlike Common Chiffchaffs which normally do not moult any primaries at all during their first winter.
Photo revealing details of the wing formula (see below). Also note the spiky looking bill. Photo © Richard Lowe
Below I have cropped a section of the above photo rotated it and reversed the image to match and allow easier direct comparison with the wing formula illustrations in Demongin. Photo © Richard Lowe
The tail often appeared quite long and appeared to have a mix of rounded and more pointed and worn tips It was jerked slightly up and down when singing but the bird lacked the constant tail dipping of Chiffchaff only doing so much less frequently with less deep dips.
Plumage:- The overall plumage of the bird morphed from quite dull under the shade of the canopy to quite bright when seen in better light. The crown and mantle morphed from appearing a drab olive-brown and Chiffchaff like in some lights, but appeared brighter tending towards a hint of more Wood Warbler-like green when seen in better light.
The rump appeared uniform with the rest of the upperparts, though due to the hump on the lower back the rump could appear slightly brighter green from some angles at times. There often tends to be more of a slight contrast with a brighter more yellowish-green rump and browner back and mantle on Chiffchaff, something which I checked and saw on several nearby Chiffchaffs.
The scapulars were similar in colour to the mantle and mostly covered the wing coverts but the greater coverts could be seen to have paler greyish white tips and fringes, these forming a faint wingbar at rest. The primaries and secondaries were edged with quite bright yellowish-green. The tertials also had similar broad green outer fringes becoming paler more buffish-white towards the tip and this colouration continued narrowly up the inner fringe. The primary coverts appeared rather worn and slightly faded with worn greyish fringes contrasting with the brighter green fringes of the primaries. The appearance of the underparts also varied with the light conditions but overall appeared noticeably whiter and less dingy than nearby Chiffchaffs. The throat appeared mainly white with yellow streaking at the sides. Yellow cascaded down from the fore-supercilium below and in front of the eye continuing down the sides of the throat to join a diffuse band across the breast. In some lights this appeared more buffish while in other light conditions it could appear bright yellow. From here yellow streaking continued along the flanks leaving the belly clean white. The vent was contrastingly yellow though good light was required to see this. In bright sunlit conditions the yellow tones often “burned out” and were less obvious.
The supercilium was quite long and was bordered below by a slightly darker eyestripe than most Chiffchaffs resulting in a slightly more strongly marked face pattern. It was a rather bright yellow (depending on light conditions) above and in front of the eye contrasting with paler buffish-white behind the eye (a character often associated with Iberian, though some Chiffchaffs can appear similar). Sometimes a faint slightly darker line was also visible bordering the upper edge of the supercilium. The eye-ring overall appeared less obvious than on a typical Chiffchaff, being restricted to a rather thin whitish arc below the eye, the upper part being yellow and blending into the fore supercilium. The ear coverts when seen well in a side on view appeared quite pale merging gradually with the sides of the neck and throat, though from some angles, such as head on views, they could appear to be darker.
The bill was a striking feature usually appearing very pale. the lower mandible was entirely orangey-yellow, sometimes appearing to darken very slightly towards the tip when the bill was closed, though this appeared to be due to the dark of the upper mandible showing through, as when the bill was open while singing it appeared entirely pale. The upper mandible was also extensively pale along the cutting edges just leaving a narrow darker area along the culmen. The gape was also strikingly yellow, more so than on a typical Chiffchaff. The legs often appeared a darkish brown when seen up in the canopy but when seen well in better light and closer views they were obviously quite pale reddish brown and when backlit they could appear strikingly pale.
Below I have included a few recordings of the bird. These were recorded on my phone so they are not high quality or very loud and are probably best heard with headphones.
For the first week despite many hours of observation I heard it sing nothing but a distinctive short 3-31/2 seconds long phrase with only very slight variation (which I have called Song type A). To me this had something of the tone of Iberian Chiffchaff but lacked the distinctive “Wheet Wheet wheet” section though it did often appear to have a shortened version of the rattle of that species. On sonograms it can be seen there are a mix of rising notes (forward slashes) and falling notes (backslashes) which is a typical pattern on sonograms of Iberian Chiffchaff song. Link to Song type A here.
The phrases and number of notes per song favoured Iberian as well as being restricted to below 7khz though there are some Chiffchaff like notes in there. The song was clearly aberrant for either species and it sang nothing but slight variations on this (Song type A) for the first week or so. The following week it continued with the same song but I heard it sing a more Chiffchaff- like song (which I have called song type B) twice, both times in response to a nearby Common Chiffchaff getting closer.
It is not unusual for an Iberian Chiffchaff to sing Chiffchaff like phrases and this has sometimes been given the name conflict song as they often use it response to encroaching Common Chiffchaffs as well as other Iberian Chiffchaffs. They are also capable of learning/imitating the song of Chiffchaff in the absence of their own kind, perhaps similar to this. Gradually these type of songs became more frequent over the following weeks and by 15th May I only heard it use type A song on a couple of occasions, mostly using type B, probably in response to the four surrounding singing Chiffchaffs. On 22nd May virtually all songs were of this type while I was there, though I still found it quite easy to pick it out from nearby Chiffchaffs due to some slight tonal differences, often including odd extra notes and most phrases still lasted three – four seconds, though occasionally it was capable of doing slightly longer songs. Here is a link to song type B. The bird at Portland in 1999 also only sung this type of song over the few hours I was watching it. This was quite late in the birds stay at Portland where it had apparently switched from a more Iberian-like song early in its stay to learning/imitating the song of Chiffchaff later -see here. The other two I had seen previously at Wentwood Forest and Potteric Carr both sang more typical Iberian Chiffchaff songs, though the Potteric bird also did some Chiffchaff-like songs while I was there. Interestingly I never heard any of these previous three birds call despite several hours of observation, they do seem to be less inclined to call than Common Chiffchaff. The finder of the Potteric Carr bird also never heard it call despite numerous visits (Yorkshire Birding Vol 19 No2 pp 38-40).
For the first week it steadfastly refused to call whereas nearby Common Chiffchaffs often started calling as soon as they stopped singing. On one occasion I probably heard it call twice in quick succession with the distinctive Siskin like call of Iberian but the bird had moved just out of sight and unfortunately I was not recording at the time and although lots of Siskins were present in the area I’m pretty sure none were nearby when I heard this. Finally on 30th April the bird was singing close by as I was examining sonograms on Xeno Canto when I accidentally played the call of Iberian Chiffchaff on my phone upon which the bird immediately flew into the tree above me and began calling excitedly for several minutes, uttering it’s fairly quiet Siskin-like call about once every second. I managed to record this on my phone and produced the sonogram below. Here is a link to listen to the call . Note the calls are fairly quiet but can be heard between the much louder burst of Wren song.
Calls represented by the small dashes about one second apart between the much louder bursts of Wren song.
On the sonogram these appear as short backslashes just below 5khz falling to about 4khz. I checked these calls against the ones on Xeno Canto and many of the calls on there start at or just below 6khz falling to about 4khz though there are calls on there with similar frequencies to the Farley bird such as XC482529 on page 4, XC550109 on page 8, XC 337248 on page 10 and XC399778 on page 14 for example. Also check out the sonograms of the calls of the first Irish record at Brownstown Head (sonograms at the bottom of the page). Some of the individual notes on the sonogram have a faint ascending element before the descending section but the emphasis is on the descending part, compare with these call sonograms from Portugal here at Soundbirding.
Discussion I enjoy a challenging ID, though this one has been quite extreme, taking up many hours of observation. Due to its aberrant song the question of hybrids mixed singers and song switching complicates matters in an already difficult ID, but it has also been educational, forcing me to finally venture into the world of sound recording and producing sonograms, something which I have been putting off for some time.
Aberrant song is quite common with many species, I regularly hear Chiffchaffs with unusual or aberrant songs with many different versions but all usually have typical a distinctive Chiffchaff character and are readily identifiable as such.
Song switching is not uncommon between Willow Warblers and Chiffchaffs, I have personally come across at least ten such birds in the past and there are two Willow Warblers currently at Ogston which both sometimes sing Chiffchaff like phrases and both also mimic part of the songs of other species. Here is one starting off with a Chiffchaff phrase then shortly after starts with a Great Tit like “teacher teacher” morphing into normal Willow Warbler song listen here. This bird also appears to have learnt part of the song of a Wren, often starting off like the beginning of a Wren’s song and seamlessly switching to normal Willow Warbler, listen here. It also sometimes starts with the rattle like part of a Wren’s song. The other bird regularly sings Great Tit like phrases even more often, and interestingly both these birds appear to be unmated. Both these birds and all the other previous birds I have seen have appeared to be normal Willow Warblers and this is apparently usually the case that the vast majority of birds singing phrases of both these species appear to be pure Willow Warblers, though there is apparently at least one case of a genetically pure Chiffchaff singing Willow Warbler-like phrases. I suspect that Chiffchaff like phrases are probably an ancestral trait shared between Chiffchaffs, Iberian Chiffchaffs and Willow Warblers as all three use them fairly regularly, the case of Chiffchaff using Willow Warbler phrases mentioned above seems more likely to me to be a case of imitation.
True mixed singers include elements of two species mixed up in the same song phrase and don’t really sound like either species. Some hybrids between Willow Warbler and Chiffchaff can produce a song that apparently resembles the song of Iberian Chiffchaff, though the few recorded examples I have heard have not sounded anything like the Farley bird and they tend to have the wrong phrasing and frequency. Most mixed singers in the overlap area between Iberian and Common Chiffchaff have been proven genetically to be hybrids, though not all as some mixed singers were pure individuals of either species, and some hybrids sing the normal song of either species, so clearly imitation or learning the wrong song plays some part in this.
More detailed information on song switching and mixed singing can be found in The Sound Approach to birding pages 129-31 and on Alan Dean’s website here
To identify the Farley bird it is necessary to eliminate all other possibilities. Willow Warbler can quickly be ruled out due to the emarginated P6 visible in several photos. I would expect a hybrid between Willow Warbler and Chiffchaff to show more intermediate characters and lack the moult pattern. A hybrid between Chiffchaff and Iberian Chiffchaff is more difficult to rule out, however the wing formula and the moult pattern of the Farley bird, close to the extreme limits for Iberian (six outer primaries) all seem to me to point more towards a pure Iberian and I suspect that it is one from a late brood bird, or perhaps one born in an out of the normal range location and thus not exposed to/able to learn typical Iberian Chiffchaff song. Song type A seems to me to be an innate version of Iberian song, having the phrasing number of notes and frequency typical of that species. The structure of the song alternating between descending notes (backslashes) and rising notes (forward slashes) also seems typical of Iberian to me. Type B song seems typical Iberian conflict song or imitation of Common Chiffchaff. There are several very similar examples on Xeno Canto such as XC650103 on page 1, XC557546/47/51 & 52 on page 4, XC142769 on page 15, compare the sonograms of these with those of song type B above.
I have previously put a couple of shorter posts up with brief notes on the appearance, deliberately not trying to influence the opinions of anyone prepared to comment on its identity. The few people who have expressed an opinion verbally have all been in favour of Iberian Chiffchaff I suspect most others have been waiting for someone to pronounce what it is. Clearly I believe it was most likely an Iberian Chiffchaff but it was not too surprising in view of the aberrant song that it was found to be not proven by BBRC.