Bradshaw: Moustached WarblersFrom in Britain the RaritiesBradshaw: Moustached Warblers in Britain Committee’s files Identification of autumn Isabelline Wheatears

he Isabelline Wheatear Oenanthe 1. Structural isabellina is surely one of the most • Larger size Tdifficult of British rarities to identify. • Longer legs This is due partly to similarities with • Shorter tail Northern Wheatear O. oenanthe in autumn • Stouter bill plumage, partly to the variability of Isabelline • Shorter primary projection and Northern Wheatears, and partly to • Slightly larger head with flatter crown varying and sometimes contradictory state- ments made in the identification literature. It 2. Behavioural is, however, not only the identification of • More upright stance Isabelline Wheatear that is difficult, but also • Bounding or running gait the assessment of claimed records, which • Head-bobbing and tail-wagging can be an extraordinarily problematical task, sometimes made more so by the receipt of 3. Plumage inadequate material on which to pass judg- • Lack of contrast between the upperparts ment. For species that combine great scarcity and wings with the degree of subtlety in characters • Lack of contrast between the upperparts exhibited by Isabelline Wheatear, we demand and underparts the most detailed notes, together with, • Supercilium whiter and more prominent where possible, identifiable photographs of in front of eye, fading quickly behind the individual concerned. • Ear-coverts almost concolorous with rest The major identification features of of upperparts Isabelline Wheatear were discussed by • Lores variable, depending on angle and Clement (1987), and these are being updated wear, but eye-stripe fading behind eye for the text of his forthcoming book on the • Lack of contrast in wings, especially identification of wheatears. Corso (1997) tertials and coverts took a novel approach to this identification • White of rump starting lower down the problem by investigating the variability of back Isabelline Wheatear. While we would not • Broader terminal black tail band and necessarily agree with all of its findings, that shorter stem of ‘T’ paper does provide an essential reference for • Whitish underwings anyone interested in this identification chal- • Isolated black alula lenge. The BBRC files have details of 16 accepted records, as well as several reports Using Corso’s analysis, the features that were rejected. I examined descriptions showing least variability and highest relia- and photographs of the autumn records in bility, in no particular order of ranking, are: an attempt to identify common themes (a) shorter primary projection; (b) super- occurring in the accepted descriptions, and cilium not ‘flaring’ behind eye; (c) ear-coverts then assessed whether or not these points of of same colour as rest of upperparts; (d) detail were present in the records that had general lack of contrasts in pattern of the been found unacceptable. whole bird; (e) lack of contrast in upper- Perceived wisdom has it that the identifi- wing; (f) isolated black alula; (g) white under- cation of Isabelline Wheatear in autumn can wing; and (h) tail pattern. Corso (1997) felt be made by using the following criteria, all in that the variation in size and shape within comparison with Northern Wheatear (P. Northern and Isabelline Wheatears, coupled Clement in litt.): with the necessity for direct comparison and

488 © British Birds 93: 488-492, October 2000 Bradshaw: Identification of Isabelline Wheatears significant experience of both species, meant that almost all structural and particularly behavioural features, such as tail-wagging and gait, were of little value in identification of an individual bird. In Britain, this problem is compounded by the fact that structural and size variations of Northern Wheatear are even greater than in Italy, as Britain is regu- larly visited by moderate numbers of the larger ‘Greenland’ Wheatear O. o. leucorhoa; this subspecies is not only larger, longer- legged and larger-billed than the nominate race, but is also often paler and frequently tends to show rather more black on the tail. Moreover, observers in Italy see both Isabelline and Northern Wheatears with some regularity, and often have the opportu- nity of viewing them side by side. In Britain, by contrast, many wheatears are seen by birders for whom Isabelline is not an everyday occurrence, and a putative Isabelline may turn up without an accompa- Colin Bradshaw nying Northern Wheatear for direct compar- ison. 288. Isabelline Wheatear Oenanthe isabellina, Kilnsea, East Yorkshire, October 1990. Descriptions of most of the accepted British records of Isabelline Wheatear include all of the features highlighted by as Isabelline Wheatear not only had broad Corso (1997), and many of the others. British pale buff fringes, lacking any rusty tones, to observers set a lot of store by structural com- the tertials, secondaries and coverts, but the parisons, with most descriptions detailing… ground colour of the feathers was also not ‘a large-headed, robust, pear-shaped black or dark brown but mid brown or grey- wheatear’ with ‘upright stance, long legs and brown, thereby lessening contrast with the short tail, giving a pot-bellied look’. The pale fringes.This produced a less contrasting, majority of descriptions include mention of more uniform wing. When the wing was the isolated black alula, the white underwing closed, the darker centres to the lesser and (although admitting how difficult this was to greater coverts and secondaries were usually see), and the broad black tail band and completely obscured by the fringes. The restricted white on the rump. Most centres of the median coverts, however, observers seem unaware that this last feature sometimes showed through as indistinct is due to the fact that the sandy-brown dark freckles near the bend of the wing, but colour of the mantle extends onto the upper this was quite different from the ‘string-of- rump of Isabelline Wheatear, creating a more pearls’ effect often seen with the dark- restricted area of white than on Northern centred median coverts of Northern Wheatear, and they believe that this is a Wheatear.The mid-brown centres of the ter- result of lack of white on the tail (plate 288). tials are always visible, but lack the obvious Interestingly, all the records that have been contrast between the blackish centres and deemed unacceptable also detail all these pale edges shown by Northern Wheatear.The structural and plumage features. general effect of the browner centres to the What, then, are the criteria that separate wing feathers, combined with the broad buff the acceptable from the unacceptable? In fringes, is to reduce the contrast between the series of records that I examined, the the wing and the rest of the upperparts, pro- most important factor was the level of crit- ducing a more uniform appearance. ical detail provided on the patterns of the Descriptions of the head pattern varied, wings and the head. Autumn birds accepted but almost all mentioned a supercilium

British Birds 93: 488-492, October 2000 489 Bradshaw: Identification of Isabelline Wheatears

which was most prominent before the eye, Wheatear O. deserti before John McLoughlin rapidly fading behind. This was accentuated correctly identified it, on the basis of the by a dark line (varying from thick black to general plumage, head pattern and pale indistinct brown, flecked pale) across the underwing. Plate 289 shows the uniform lores, which disappeared, or became only a plumage, the relatively plain head pattern, shadow, along the upper border of the ear- with an indistinct supercilium before the eye coverts, which were the same colour as, or only, and a dark loral line that fails to extend only a shade darker than, the crown and behind the eye.A similar bird was present on nape. Most of the acceptable records also Whalsay, Shetland, in September 1994 (Brit. detailed how the facial pattern changed con- Birds 88: 534). Once again, this individual siderably when viewed at different angles was not noticeably larger or longer-legged and in different lights. In particular, the dark than Northern, nor was the stance particu- loral line appears more prominent when the larly different. It, too, was identified predomi- bird is viewed front-on, as the observer is nantly on plumage characteristics. looking down the forward-pointing dark- The third exception to the rules involved based feathers. Often, the birds were thought a well-watched bird on Gugh and St Agnes, to be extremely plain-faced until seen head- Isles of Scilly, in October 1991 (Brit. Birds on, when a noticeable supercilium became 85: 537).This individual was, in many ways, a apparent. typical Isabelline in size and structure, and Four notable exceptions to these rules the head pattern was extremely variable, were found, all involving undoubted depending on light and also on the angle at Isabelline Wheatears. The first, and perhaps which it was being watched. Plate 292 the most dramatic, was the small individual shows a characteristic view of it, with the at Kilnsea, East Yorkshire, in October 1990 supercilium more marked in front of the eye (Brit. Birds 84: 483). This bird (plate 289) and narrowing quickly behind, uniform ear- was the same size and shape as nearby coverts and an almost negligible eye-stripe Northern Wheatears. It was neither long- behind the eye; also shown is the typical legged nor particularly short-tailed, and the primary extension, the mid-brown centres to bill was quite weak, although photographs the tertials, the centres to the secondaries suggest that it could also give the opposite and greater coverts completely obscured by impression (plate 290). Because of its size the broad pale fringes, and the darker and colour, and an almost complete black ‘freckles’ around the median coverts. Plate tail, it was initially misidentified as a Desert 291 of the same individual, in different light, Colin Bradshaw

289. Isabelline Wheatear Oenanthe isabellina, Kilnsea, East Yorkshire, October 1990 (same individual as in plate 288).

490 British Birds 93: 488-492, October 2000 Bradshaw: Identification of Isabelline Wheatears however, shows a supercilium at least as pendent’ scrutiny.The descriptions should be prominent behind the eye and, if not detailed and should concentrate at least as ‘flaring’, at least remaining parallel for the much on plumage as on size and jizz. It is not length of the ear-coverts. This photograph sufficient merely to say that there was ‘little also shows the extent of the white on the contrast on the wing’, as we need the rump, the upper border falling between the reasons why this contrast was absent. Simi- tips of the middle and longest tertials, larly, we do not expect to read simply that whereas, on Northern Wheatear, the corre- ‘there was an obvious black alula’: we need sponding mark is higher, usually just above to know how this related to the other parts the tip of the middle tertial.The final unusual of the wing, what was seen on the primary record was of a bird trapped at Girdleness, coverts, why it stood out so much, how Grampian, in October 1979 (Brit. Birds 73: many feathers were involved, and how often 519-520), which displayed a supercilium that the alula was seen. We do not require just a was whiter and more obvious behind the simple description of the head pattern, but eye than in front. need to know how it varied in different What would an ideal record of an views.Alongside this, we also need details of Isabelline Wheatear look like? Well, first of size and shape. An example of an ideal all, the bird should have been seen by several Isabelline Wheatear description was pub- competent observers, and the record should lished by us in 1993 (Dean 1993). preferably be supported by photographs. It is important to remember that there are This is not because we disbelieve single two accepted British records of individuals observers, but, for subtle identifications such that failed to show the structural characteris- as this, it is possible for a lone observer to go tics of typical Isabelline Wheatears, but none off at a tangent and become convinced that involving birds of which the plumage was he or she is watching an Isabelline Wheatear imprecisely described. when it is actually a large, pale Northern Wheatear.This is slightly less likely to occur References when several people see the bird. Groups of Clement, P.1987. Field identification of West Palearctic wheatears. Brit. Birds 80: 137-157, 187-238. observers should always expect us to want Corso,A.1997.Variability of identification characters of to compare several separate descriptions Isabelline Wheatear. Dutch Birding 19: 153-165. when assessing a record, looking for dif- Dean, A. R. 1993. From the Rarities Committee’s files: ferent emphases that build up the full Isabelline Wheatear in Scilly. Brit. Birds 86: 3-5. picture. Photographs also allow some ‘inde- Colin Bradshaw

290. Isabelline Wheatear Oenanthe isabellina, Kilnsea, East Yorkshire, October 1990 (same individual as in plate 288).

British Birds 93: 488-492, October 2000 491 Bradshaw: Identification of Isabelline Wheatears Colin Bradshaw

291 & 292. Isabelline Wheatear Oenanthe isabellina, Gugh, Scilly, October 1991. Colin Bradshaw Colin Bradshaw 9 Tynemouth Place, Tynemouth, Tyne & Wear NE30 4BJ

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492 British Birds 93: 488-492, October 2000