Largely thanks to being a warmer 'refugia' during the ice ages, Iberia is unique in Europe for being the home of several endemic or near-endemic birds most notably Azure-winged Magpie, Iberian Green Woodpecker and Spanish Imperial Eagle (although the latter was once found more widely). If one extends the list to include nearby North Africa then the list becomes still longer: Red-necked Nightjar, Spanish Yellow Wagtail, Black Wheatear, Thekla Lark and Western Olivaceous Warbler. Thanks to developments in DNA based taxonomy another species, Iberian Chiffchaff, has now been added to that list.
Iberian Chiffchaff (Phylloscopus ibericus) belongs to a group of similar tree haunting small and largely nondescript birds that we British once called 'willow-wrens'. Whilst we've lost any colloquial name for these birds, the Spanish have retained theirs and call them all, charmingly I think, “mosquiteros” (= mosquito eaters). In many ways the most interesting of these is Mosquitero Ibérico or Iberian Chiffchaff. Given that British ornithologists regularly explored Gibraltar's hinterland from at least the 1860s onwards, despite the similarity in plumage, it seems surprising that nobody seems to have reported 'unusual' chiffchaffs in the area (esp. in the Alcornocales where they are fairly common) as the song is quite distinct. The answer seems to be that they were widely mistaken for Willow Warblers. Even the great pioneer Irby, author of the seminal 'Ornithology of the Straits of Gibraltar' (1875, enlarged edition 1895), appears to have been fooled as in his book he wrongly notes of Willow Warblers that in “the vicinity of Gibraltar they are to be found throughout the year in the Cork-wood, where they breed” and most subsequent authors appear to have followed his lead. Since Willow Warblers are, in fact, non-breeding passage migrants to the area, it seems that in the days before widely available recordings of bird song it was all too easy to mistake Iberian Chiffchaff's more musical cadences for a variant of this species rather than Chiffchaff.
The realisation that these birds were, in fact, chiffchaffs with distinctive song came surprisingly late in 1913. In that year, Captain Hubert Lynes studied them near Gibraltar (see - 'The Ibis' Vol II 1914 – http://www.biodiversitylibrary.org/item/100092#page/370/mode/1up) and, like those before him, Lynes initially mistook the Iberian Chiffchaff's tripartite song as a local dialect, not of Chiffchaff but Willow Warbler. However, unlike others, he carefully investigated the situation. On finding a nest and collecting a specimen he realised he'd made an error and that the birds were a kind of chiffchaff. It's worth quoting Lynes' perceptive note more fully: “The only other breeding Phylloscopus (so far as we could find), was by its song, I think anyone would have agreed, a Willow-Warbler; singing males of this species shared the cork-oak glades in about equal proportion as Bonelli's. For a Willow-Warbler, true, the song was unmelodious and disjointed (“tin-potty”, if one may use such an expression), the first two notes jerked out, so that for a moment they might have been put down to an eccentric Chiffchaff, had they not invariably been followed by the four or five notes in descending scale characteristic of the Willow Warbler – in short, if it was a poor Willow-Warbler's song, it was an impossible Chiffchaff's”. He went on to relate how found a nest and eggs (which more resembled that of a Chiffchaff than a Willow Warbler) and shot the female. On examining the latter and a further six specimens he collected, he found that “with no little surprise” it possessed “all the external characters, dimensions, wing formula, emargination, etc of the typical Chiffchaff” and, although he noted the plumage was largely the same as British birds he observed that “the sulphur yellow axillaries may be a trifle brighter.” Lynes went on to note that, unlike the plumage, “the peculiarity of the song, which is constant, must have some significance” and then discussed whether the birds were resident in the area (as widely assumed) or were, in fact, migrants. It's perhaps unfortunate that Lynes seems to have collected his birds in early June when they would have been at their most worn and least likely to show their greener and yellower plumage. Had his birds shown the recognised traits of a 'good' ibericus then perhaps greater notice would have been taken of his observations. Even so, it's a little surprising that, although extensive reference was made to the Canarian race of Chiffchaff neither, he nor H F Witherby (whom he consulted) made any reference to the Iberian race of chiffchaff described over 40 years earlier. (Rear-Admiral Lynes, as he became, enjoyed a distinguished naval career retiring in 1919 after which he led several ornithological expeditions in Africa on whose birds he was an authority. Not daunted by a challenge, he wrote an important review of Cisticolas, the ultimate LBJs, for the journal “Ibis” and Lyne's Cisticola Cisticola distincta is one of over a dozen bird species and subspecies named in his honour).
As noted above, even those with access to older books specifically touching upon the birds of Spain will find that neither “Iberian Chiffchaff” nor the odd song of the form gets a mention at all. At one level the continuing omission of this form in the popular literature is not surprising since, even today, Iberian birds are regarded as doubtfully distinguishable on plumage grounds alone but at another level it's a surprise that the distinctive song and the fact that birds in much of Iberia belonged a distinct race went unmentioned for so long. That the popular ornithological literature virtually ignored these interesting birds until relatively recently is still more od a surprise as bred in such an accessible and ornithologically well-known area. Nobody seems to have followed up or to have shown overmuch interest in Captain Lynes' work (with the evident exception of Claude Ticehurst about whom see below). Although both Roger Tory Peterson and Guy Mountfort (illustrator and author respectively of the first European bird field guide) were part of the famous team that explored the Coto Donana neither their field guide nor the latter's book about the expeditions, “Portrait of a Wilderness” (1958), mention that the local chiffchaffs had a unique song. Yet a fellow member of their team (and subsequent reviser of their guide) I. J. Ferguson-Lees, later demonstrated that he clearly knew the bird's distinctive song. Not surprisingly when a bird singing like ibericus was found in London in 1972 the finder, despite being a highly regarded ornithologist, had never even heard of the distinctively different Iberian form and the bird's identity was resolved, not from any printed reference, but on playing a recording of the bird to I. J. Ferguson-Lees. Even so, the record was only accepted almost 30 years later (see - https://britishbirds.co.uk/wp-content/uploads/article_files/V93/V93_N07/V93_N07_P329_332_A005.pdf ).
The level of confusion regarding ibericus in the textbooks and particularly the lack of illustrations is understandable given that even the latest “Collins Bird Guide” recognises that “many are impossible to identify in the field on plumage characters”. This confusion also extended to what the bird should be called scientifically. Although for simplicity and clarity I have called it ibericus, until recently most (but not all) books called it brehmii. Changing a bird's scientific name more than a hundred years after its apparent discovery is not unknown but it remains somewhat unusual. The compelling reasons for the change is explained when one looks a little deeper into the history of Iberian Chiffchaff. In 1871, Eugen Ferdinand von Homeyer (1809–1889) first described what was later assumed to be this form from specimens collected in Iberia in April which he named Phyllopneuste brehmii after the German scientist Alfred Brehm (1829-1884). The family name was later changed to “Phylloscopus” and, given their very close similarity, recognised as being only a subspecies of Chiffchaff. Hence it the birds became known as Phylloscopus colybita brehmii. Just how 'similar' to Common Chiffchaff these specimens were was only fully recognised in 2001 when a scientific paper (see - http://biostor.org/reference/111838) revealed that the birds he described were actually Common Chiffchaffs! As a result, the old name brehmii had to be dropped. This meant that the first accurate formal description of the different taxon found in Iberia was made much later in 1937 by C B Ticehurst in his A Systematic review of the genus Phylloscopus who had called them ibericus. Unlike Von Homeyer, Ticehurst described his birds as being greener above and more yellow below so even without reference to the specimens it is clear that his birds were what we now call ibericus.
Unfortunately, this new insight into chiffchaff speciation came a little late for the 'Atlas de las Aves Reproductoras de Espaňa' (2004) which was based on survey work carried out 1998 – 2002. Understandably, the failed to adequately distinguish between the two species which resulted in an overestimate of the Iberian's range (see map). Hence, at first, it was wrongly thought that pretty much all of the birds breeding in Spain and Portugal, apart from the central and eastern Pyrenees, were Iberian Chiffchaffs.
However, the situation now seems rather more complex with De Juana & Garcia ("The Birds of the Iberian Peninsula") showing Common Chiffchaff as a thinly spread breeding species across much of the northern Meseta south of the Cantabrians with a recently discovered outpost in the Sierra Nevada. Leaving aside the North African population, it now seems that Phylloscopus ibericus is found in four main areas; western Portugal, the Sierra Morena (where it's thinly scattered), the mountains of Cadiz/Malaga and the north-west (i.e. Cantabrian massif of north-west Spain and the western Pyrenees plus just over the border into south-west France). The latter population is sometimes regarded as a race, biscayensis, based on marginal differences but this is a matter of dispute. In addition, the Spanish atlas shows isolated breeding records of 'chiffchaffs' dotted across the peninsula; presumably those towards the north-east are more likely to be 'Common' and those to the west ibericus (although given the recent breeding record of the latter from Wales anything seems possible!). Where the two species meet a small number of “mixed singers”, often regarded as hybrids, may be found. A new Spanish atlas is currently in progress so it will be interesting to discover what it tells us about this previously overlook species.
The relatively recent interest in Iberian Chiffchaff owes much to the rise of DNA-based taxonomy. In the late 1990s, research suggested that the difference in the DNA of some races of Chiffchaff was as great as that between widely recognised 'full' species. This, together with differences in vocalisations, suggested that Iberian Chiffchaffs were in fact 'cryptic' species sufficiently different to be regarded as 'full' species too. Typically, birdwatchers take a lot more interest in birds they can legitimately tick! Exactly how these birds differ (if at all!) from Common Chiffchaff in plumage and structure I shall return to in a later post but the fact is that, as Irby et al discovered, they remain similar enough to be very easily confused. Vocalisations and phenology, rather than plumage, are often the best guide.
About me ...
Hi I'm John Cantelo. I've been birding seriously since the 1960s when I met up with some like minded folks (all of us are still birding!) at Taunton's School in Southampton. I have lived in Kent , where I taught History and Sociology, since the late 1970s. In that time I've served on the committees of both my local RSPB group and the county ornithological society (KOS). I have also worked as a part-time field teacher for the RSPB at Dungeness. Having retired now spend as much time as in Alcala de los Gazules in SW Spain. When I'm not birding I edit books for the Crossbill Guides series.