There can be few more eagerly awaited autumn migrants than the small wing-barred Phylloscopus warblers. Three species in particular – Pallas’s, Yellow-browed and Hume’s Leaf Warblers – are among the most delightful birds on the British list, being tiny, hyperactve and jewel-like. An encounter with any of them is guaranteed to brighten up even the dullest autumn day. Not only are they beautiful but they also grip our imagination.
They are from distant and remote parts of Asia, and each one which reaches Britain has performed a remarkable and somewhat mysterious feat of migration. We still have much to learn about why they arrive here and what happens to them beyond their fleeting presence around our coasts.
All three species favour, where possible, those places where late insects can be found, notably clumps of sycamore and sallow, and will also readily attach themselves to winter flocks of tits and other small birds, as they do in Asia, although they then move even faster and are easy to miss.
Pallas’s Warbler
This species breeds across southern Siberia and winters in southern China and South-East Asia. Before the 1980s it was a near-mythical rarity in Britain and indeed on the Continent. The first European bird was collected on Heligoland on 6 October 1845 and the first for Britain was shot at Cley, Norfolk, on 31 October 1896. Since 1982, however, there has been a remarkable (though still largely unexplained) upsurge in records, and this beautiful bird is now an expected feature of late autumn, with some years seeing as many as 200300.
They are found from early October through to late November, the first often in the Northern Isles and later birds mainly along the south coast and in the SouthWest. Mostly this is an east coast bird, however. It is still rare inland and in the West Country.
Pallas’s Warbler is a truly tiny bird. Compact, large headed and short tailed, it is barely bigger than a Goldcrest, but incomparably brighter.
A typical view is of a tiny jewel of a bird, all bright green above and whitish below, and adorned with broad bright yellow supercilia, bulging before the eye. It has a strong dark eyestripe, dark crown sides with a sharply defined yellow central stripe, broad yellow double wing-bars, white tertial edges and a neat ‘postage stamp’ of a yellow rump.
Pallas’s Warbler habitually hovers, picking insects off the underside of leaves, almost with the skill and dexterity of a hummingbird; it can hang upside down like a tit, too. It is the brightest of the three species discussed here and on a dull autumn day it can positively gleam from the shady recesses of an autumnal sycamore.
Its call is quiet and easily missed: a soft, fruity, slightly finch-like chewit.
Yellow-browed Warbler
This species has a larger and more northerly range, breeding right across Siberia and reaching as far west as the northern Urals. It winters commonly throughout southern China and South-East Asia.
The first was collected at Hartley, Northumberland, on 26 September 1838, but there were relatively few subsequent records until the 1960s. Since then there has been a massive (also unexplained) increase in occurrences.
It is now the commonest of the autumn scarce migrants, with several hundred recorded in most years. Multiple arrivals are now routine on the Northern Isles, at favoured sites on the east coast and on Scilly, where it can be the commonest warbler species. It remains rare inland and in the West Country.
It arrives earlier than Pallas’s Warbler, normally from mid-September, but occurrences can continue into November. The peak, however, falls in late September and early October. In recent years a few have also wintered, mainly in the South-West. There is a mere handful of spring records.
Slightly larger than Pallas’s Warbler, it is still a tiny bird, though a little less compact, large headed and short tailed. It also lacks the sustained hovering capability of Pallas’s Warbler. It is bright, though not quite as jewel-like as Pallas’s. It has a slightly weaker face pattern, a more yellow-cream supercilium, a paler crown with no central stripe (although a weak paler centre may be present) and no pale rump. The creamy-yellow wing-bars and white tertial edges are, however, broad and prominent.
Unlike its congener it is very vocal and is very often first located by its call, a quite loud, high-pitched, penetrating, rising tse-weee.
Hume’s Leaf Warbler
This is the southern montane counterpart of Yellowbrowed Warbler. Breeding in the mountains of Central Asia, it winters on the Indian subcontinent. Though previously regarded as a subspecies of Yellow-browed Warbler, its distinct morphology and vocalisations are now well understood.
This is by far the rarest of our trio in Britain, with the first frequenting Belle Tout Wood, Beachy Head, East Sussex, from 13-17 November 1966. Since then another 120 have occurred as of the end of 2011. As with the other species, there is an upward trend, with a record 29 in 2003.
This is a bird of late autumn, occurring in late October and November (at the same time as Pallas’s Warbler), and again the east coast has amassed the lion’s share of records. A few have also overwintered.
In size and structure this species is essentially identical to Yellow-browed Warbler. Its plumage is, however, duller, more grey-green, less bright green above and more ‘sullied-looking’ below. Its face pattern is blander and may be suffused with buff, and its wing-bars and tertial edges are less boldly defined and contrasting. Indeed, its median covert wing-bar may be almost absent. Its bill and legs are predominantly dark, lacking the obvious brighter orange hues of its Siberian counterpart.
Somewhat surprisingly, it has two call types: a cheery, rising che-wee, slightly reminiscent of Greenish Warbler, and a down-slurred swee-oo with a harsh, almost House Sparrow-like quality.
THIRTEEN: Hume’s Leaf Warbler (Spurn, East Yorkshire, 13 May 2009). With a plain crown and no pale rump patch this is clearly either a Yellowbrowed Warbler or a Hume’s Leaf Warbler, but it is a worn bird in spring and therefore potentially more problematic to identify. As the winter progresses, Yellow-browed Warblers become duller and drabber, the bright contrasts being much reduced and the wing-bars and tertial fringes less prominent. By spring, therefore, they exhibit many of the features associated with Hume’s Leaf Warbler. This bird shows the darklooking bill typical of Hume’s, but its identity would be most easily established by hearing it call.
THREE: Yellow-browed Warbler (Uto, Finland, 8 October 2010). This delightful image perfectly captures the jizz of Yellow-browed Warbler – small, elegantly proportioned and stripy. Its face pattern is typical, with a long, narrow supercilium, good dark eyestripe and mottled ear coverts. The supercilium is creamy (rather than yellow) and the prominent greater and median covert wing-bars are whitish, similar in tone to the tertial fringes. The plain crown and rump provide final evidence that this is no Pallas’s Warbler, while Hume’s Leaf Warbler is eliminated not only by the bird’s bright plumage hues and strong wing markings, but also by the extensively pale-based bill and orange-tinged legs.
FOUR: Hume’s Leaf Warbler (Wells Wood, Norfolk, 3 December 2010). Note the very drab, almost ‘dusty’ hues on this bird. The upperparts are a cold grey-green and the prominence of the wing-bars and the tertial fringes is much reduced compared with Yellow-browed Warbler. There is no obvious median covert wing-bar and that on the greater coverts is both narrow and slightly sullied grey. The dark bar across the base of the secondaries, so noticeable on both Pallas’s and Yellow-browed Warblers, is also reduced in prominence. The face pattern is strikingly bland, with a weak eyestripe, plain-looking ear coverts and a diffuse supercilium.
TWO: Pallas’s Warbler (Uto, Finland, 13 October 2010). This bird is showing all its best features. Note the tiny size and compact Goldcrest-like proportions, with a large head, short tail and shortish bill. The plumage looks bright and jewellike. The coronal bands are dark olive and contrast with the paler rather rich moss-green mantle. The central crown stripe is narrow and sharply defined. The eyestripe is very dark, accentuating the intense facial expression. The supercilium is long, broad and liberally splashed with yellow, creating a very bright-faced impression. The wing-bars are partially hidden in this view, but the rump patch is typically prominent – a very sharply demarcated oblong of pale yellow.
SIX: Yellow-browed Warbler (Terschelling, The Netherlands, 5 October 2008). This Yellowbrowed Warbler is clearly smaller and shorter tailed than its larger leaf warbler relatives, but is not as dumpy and compact as Pallas’s Warbler. The upperparts are a paler olive and the supercilium and wing-bars, though prominent, are more white than yellow, giving a less bright appearance overall. There is, of course, no sharply defined central crown stripe (though many Yellow-browed Warblers do show a broad but weakly defined paler central area on the crown) and the eyestripe is less solid than in Pallas’s Warbler. Finally, the bill looks longish and spiky and is extensively orange at the base.
SEVEN: Hume’s Leaf Warbler (St Mary’s Wetland, Northumberland, 12 November 2008). The somewhat bland face pattern of Hume’s Leaf Warbler is shown to good effect here. The ear coverts are very plain looking, the eyestripe is weak, particularly on the lores, and the supercilium, though long, is narrow and weakly defined. The underparts are heavily sullied grey, in contrast to the whiter underparts of both Pallas’s and Yellow-browed Warblers, and contribute further to the overall drab impression. The reduced wing markings are also clearly visible, as are a largely dark bill and dark-looking legs, again in contrast to the brighter orange hues shown by Yellow-browed Warbler.
FIVE: Pallas’s Warbler (Hightown, Lancashire, 21 December 2006). Note again the compact proportions of this Pallas’s Warbler. The head looks large, the tail and bill are short and the whole bird looks rather neckless and egg shaped. As for plumage, the immediate impression is typically one of brightness and contrast – a bright yellow supercilium and wing-bars, white tertial edges, bright green mantle contrasting with a dark crown, a very dark, solid-looking eyestripe and well-marked ear coverts. Even though the diagnostic yellow rump and neat central crown stripe are not visible here, this bird is easily identifiable as a Pallas’s Warbler.
EIGHT: Pallas’s Warbler (Uto, Finland, 13
October 2010). This is a delightful image of a Pallas’s Warbler – typically compact, large headed and bull necked. The underparts are a beautiful silky white and offer an attractive contrast with the bright green and yellow hues in the head and upperparts. The face is as usual strongly marked, with dark coronal bands, a neat central crown stripe, a heavy dark eyestripe, well-marked ear coverts and a long and broad yellow supercilium, characteristically brightest above the lores. The bill is also typically short and dark looking, while the wing-bars are very yellow and contrast with the white tertial fringes.
NINE: Yellow-browed Warbler (St Mary’s, Scilly, 19 October 2011). Yellow-browed Warblers are somewhat variable in their brightness and this is a brighter bird. Nevertheless, it still lacks the vivid eye-catching brightness and sharp contrasts of Pallas’s Warbler. The greater and median covert wing-bars are white, matching the whiteness of the tertial fringes, and the upperparts are uniformly green, with no contrastingly darker crown. The face pattern is typical: a long, narrow creamy supercilium (with no extra brightness above the lores), a narrow dark eyestripe and well-marked ear coverts, while the bill and legs both show pale hues.
TEN: Hume’s Leaf Warbler (St Mary’s Wetland, Northumberland, 12 November 2008). By contrast, this Hume’s Leaf Warbler looks extremely dull. Its underparts are very heavily washed grey, reducing the contrast with the upperparts, and its face pattern is quite bland. However, it is the drabness of the upperparts and the weakness of the wing markings which really grab the attention in this image. The upperparts are a cold grey-green, the median covert wing-bar is barely present, the greater covert wing-bar is narrow and a cold greyishwhite and the tertial fringes are very narrow and inconspicuous. To complete the identification, the bill and legs also look dark.
TWELVE: Yellow-browed Warbler (North Ronaldsay, Orkney, 5 October 2007). This in-thehand Yellow-browed Warbler gives a fabulous view of its wing markings. The whitish greater covert wing-bar is stunningly broad, the prominent median covert wing-bar can just be seen and the white tips and fringes to the outer webs of the tertials are very broad and obvious. Also clearly visible here are the bright green fringes to the wing feathers and neat white tips to the secondaries and inner primaries, a feature of all three species on good views. Note also the spiky extensively pale-based bill and the typical face pattern of Yellow-browed Warbler.
ELEVEN: Pallas’s Warbler (Spurn, East Yorkshire, 27 October 2011). In this in-the-hand image it can be appreciated how tiny Pallas’s Warblers really are! The overriding impression is of stripes, brightness and contrast. Although the pale yellow rump patch is invisible here, the solid dark eyestripe, dark contrasting crown, neat narrow central crown stripe, bright yellow foresupercilium and yellowish hue to the wing-bars immediately identify this as a Pallas’s Warbler. Even though it’s in the hand, some structural clues are still shown to good effect: the rather short, dark looking, almost tit-like bill and the typically rather large-looking eye.