Review of British status and identification of Greenish Warbler A. R. Dean he traditional view, that a Phylloscopus warbler in Britain which dis­ Tplayed a single wing-bar must be either an Arctic Warbler P. borealis or a Greenish Warbler P. trochiloides, has received support in all but the most recent identification literature. During the late 1950s and early 1960s, a number of decidedly grey, drab Phylloscopus warblers, each with a single, narrow, whitish wing-bar, were observed. They were clearly too small for Arctic Warbler, with relatively short bills and the wrong bare-part colours. Knowledge that the species' range was expanding northwest in Europe continued.... [Brit. Birds 78: 437-451, September 1985] 437 438 British status and identification of Greenish Warbler encouraged a belief in Britain that these birds were Greenish Warblers. For many observers, the image of the species became based on these rather drab, grey individuals. They tended to appear rather late in the autumn and, during the 1960s, there were two mid-winter records (Perry Oaks, Surrey, and St Agnes, Scilly), remarkable for a species which normally winters in India. Later in the 1960s, however, doubts began to set in. Greenish Warblers appeared significantly later in the autumn in southern and western Britain than on Fair Isle, where a relatively high percentage of identifications was confirmed by trapping. Most trapped individuals displayed a bright and smart appearance and an intensity of greenish hues which, even allowing for the known variability of the species (Alexander 1955), were difficult to reconcile with the image of the species which was prevalent elsewhere in Britain. Evidence was also mounting that ChifFchafFs P. collybita of northern and eastern origin could display a single, quite well-defined wing-bar. On Fair Isle, such individuals were identified regularly in late autumn. In combination, these factors led R. H. Dennis to conclude that northern Ghiffehaffs were being misidentified as Greenish Warblers, and his misgivings were conveyed to the Rarities Committee. From about 1970, public awareness of the pitfall of Chiffchaffs with wing-bars became widespread and, significantly, the number of late autumn reports of Greenish Warblers subsequently declined. In 1981, the Rarities Committee began a review of all previously accepted records. This soon confirmed that the vast majority of records after 1970 was soundly based, but that a substantial percentage of identi­ fications before that time had taken insufficient account of possible confusion with Chiffchaffs of the north European race P. c. abietinus and the Siberian race P. c. tristis. Results of the review Between 1958 and 1970, records of 46 Greenish Warblers had been accepted by the Committee. Of these, 13 (all of which were trapped and examined in the hand) were clearly classic examples of the species. The remaining 33 records required closer examination. Many descriptions concentrated only on the elimination of Arctic Warbler, and gave little or no consideration to the elimination of abietinus and tristis. Eventually, 20 of the previously accepted records were rejected. A further two remain under review. Thus, of 46 previously accepted records between 1958 and 1970,24 remain accepted (Appendix 1). Distribution of accepted records The number of accepted records between 1958 and 1970 has thus fallen by more than 40%. It is instructive to compare the temporal and geographical distributions of those records which remain accepted in this period with those described by Sharrock (1971) for the period 1958-67 (which were based on all the records accepted at that time), and with the long-term trend as revealed by the entire record for 1958 to 1982. British status and identification of Greenish Warbler 439 The pattern of past-accepted records during 1958-67 indicated a peak in September and October. About 30% of the records between August and November were in southwest England and Wales (rising to 45% if Irish records were included), and around 40% on the English east coast between Northumberland and Kent. As with several species of northeasterly origin, however, the later observations were concentrated in the south and west; in north and east Britain a majority of records was in August and September. The currently perceived seasonal patterns in Britain for 1958-70 and 1958-82 are displayed in fig. 1. (Irish records have been reviewed separately by the Irish Records Panel: Mullarney 1984.) In contrast with the original indication, the revised distribution for 1958-70 is clearly compatible with the longer-term trend, showing both a peak in late August and early September, and relatively few records after the end of September. The geographical distribution for 1958-82 is displayed in fig. 2. Only 18% of the August to November records were in southwest England and Wales, while 60% were on the English east coast between Northumberland and Kent. Fig 1. Seasonal pattern of Greenish Warblers Pkyttoscopus tmchiloides in Britain during 1958-70 (black) and 1958-82 ("black plus unfilled) Thus, using the revised data, the suggestion of a significant October arrival of Greenish Warblers disappears, while the geographical distri­ bution shows a much more easterly bias. In autumn, Norfolk emerges as the county most regularly visited by Greenish Warblers (17% of the autumn total), followed by Shetland, Humberside, Lincolnshire and North­ umberland. The rather few late autumn records still tend to be in the southwest (with four of the eight October and November occurrences in Scilly), but there are single October records from Orkney and Kent. Among the scattering of spring and early summer records, six occurrences in the Isle of Man during June and July {between 1962 and 1981) are of particular note. Field-characters of Greenish Warbler and its confusion species Insufficient awareness that Chiffchaffs of the races abietinus and tristis may display a reasonably well-defined wing-bar seriously impeded the identification of Greenish Warblers during the late 1950s and 1960s. In reality, the appearance of most Chiffchaffs with a wing-bar is, in other respects, markedly different from that of Greenish Warbler, and confusion between these two species should rarely be a problem once the true 440 British status and identification of Greenish Warbler Fig 2. Distribution by counties of Greenish Warblers Phylloscopus trochiloides in Britain during 1958-82 character of each is appreciated. Among other Palearctic Phyllo­ scopus warblers with proven or potential westward vagrancy, Greenish Warbler needs to be distinguished from Green Warbler P. nitidus, Two- barred Greenish Warbler P. plumbeitarsus (these three species being very closely related), and Arctic Warbler. At certain times of the year, there is also a possibility of confusion between Greenish Warbler and the Central Asiatic race of Yellow-browed Warbler P. inomatus humei, worn adults of which may be superficially similar (personal observation, and Kitson 1980). Perhaps the only non- Phylloscopus species with which any of the above may be confused is the Nearctic Tennessee Warbler Vermivora peregrina (Browne 1960; Doherty 1984; Meek 1984). The following discussion deals primarily with the principal characters by which Greenish Warbler and 'northern' Chiffchaffs may be distinguished, and then, more briefly, describes the salient characters of other confusion species. It draws heavily on discussion in the files of the Rarities Committee, but is supplemented by an examination of skins and personal field experience of all the relevant species. The discussion is largely comparative, to facilitate discrimination between species. More-formal, British status and identification of Greenish Warbler 441 and readily accessible, presentations of biometrics and of plumage and bare-parts characters, are given in tables 1 and 2 for the six most relevant Phylloscopus species. Greenish Warbler and northern Chiffchaffs Current taxonomy divides the Greenish Warbler into four subspecies (trochiloides, viridanus, ludlowi, and obscuratus), with Green Warbler and Two-barred Greenish Warbler recognised as separate but very closely related species (see discussion in Williamson 1967). The rare viridanus breeds in northeastern Europe, and west and central Asia. It is replaced by trochiloides in much of the Himalayas and western China, by ludlowi in the northwestern Himalayas, and by obscuratus in northwestern China. In fresh plumage, the races viridanus and trochiloides are sufficiently different to warrant comment (trochiloides having darker upperparts and a much greyer, darker, and more contrasting crown), but only viridanus is likely to appear in Britain, and all trapped individuals have been attributed to this subspecies. The familiar Chiffchaff of Britain and much of western and southern Europe P. c. collybita is replaced by abietinus in northern and eastern Europe and by tristis in Siberia and central Asia (see Williamson 1967 for a more detailed account of the distribution of these and the more southerly races canariensis, exsut and ibericus). The races differ primarily in the extent and prominence of olive and yellow in the plumage. Both hues are at their greatest development on nominate collybita, while olive is very limited and yellow entirely lacking (except on the marginal coverts near the alula—'the bend of the wing'—and on the axillaries) on tristis. The race abietinus is somewhat intermediate, generally with rather greyer or browner upper- parts than collybita and rather