There can be few more eagerly awaited October birds than the wing-barred Phylloscopus or leaf warblers. Three species – Yellow-browed, Hume’s Leaf and Pallas’s Warblers – are among the most delightful birds on the British list: tiny, hyperactive and jewel-like. They are not the only options, however. The much rarer Eastern Crowned and Pale-legged Leaf Warblers, both recent additions to the British list, are also possible in October.
Yellow-browed Warbler
This species has a large and northerly breeding range across Siberia, reaching as far west as the northern Urals. It winters throughout southern China and SouthEast Asia.
There were relatively few British records until the 1960s. Since then, however, there has been a massive increase in occurrences, with many hundreds reported in most years and multiple arrivals now routine on the Northern Isles, the east coast and Scilly, all locations where this can be the commonest warbler species at times.
It occurs earlier than Pallas’s Warbler, normally from mid-September, but arrivals can continue into November, with a peak in late September and early October. In recent years, a few have also wintered, mainly in the South-West, and there have been a number 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, and it lacks the sustained hovering capability of Pallas’s. It is also bright and has a slightly weaker face pattern, a more yellowish cream supercilium, a paler crown with no central stripe (although a weak pale centre may be present) and no pale rump. The creamyyellow wing-bars and white tertial edges are, however, broad and prominent.
Unlike its congener, it is very vocal and often first located by its distinctive call: a quite loud, high-pitched, penetrating and rising tse-weee.
Hume’s Leaf Warbler
A southern montane counterpart of Yellow-browed Warbler, Hume’s breeds in Central Asia and winters in the Indian subcontinent. Previously regarded as a subspecies of Yellow-browed, its distinct morphology and vocalisations are now better understood.
This is by far the rarest of the regular tiny leaf warblers in Britain, with 139 records to the end of 2015, but as with the other species, there is an upward trend. This is a bird of late autumn, occurring in late October and November (at the same time as Pallas’s Warbler). The east coast has amassed the lion’s share of records. A few individuals have overwintered.
In size and structure, this species is essentially identical to Yellow-browed Warbler. However, its plumage is duller, more grey-green and less bright above, and ‘dirtier’ or more ‘sullied looking’ below. Its face pattern is blander and may be suffused with buff, while its wing-bars and tertial edges are less boldly defined and contrasting. Its median covert wing-bar may be almost absent. The bill and legs are predominantly dark.
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.
Pallas’s Warbler
Pallas’s Warbler breeds across southern Siberia, and winters in southern China and South-East Asia.
It was a near-mythical rarity in Britain before the 1980s, but since then there has been a remarkable upsurge in records. It is now an expected feature of late autumn, with some years seeing more than 200 records. It is found f rom early October through to late November, the first arrivals often on the Northern Isles, with later birds mainly along the south coast and in the South-West. Mostly, however, this is a bird of the east coast.
Pallas’s Warbler is a truly tiny species, compact, large headed and short tailed, barely bigger than a Goldcrest but incomparably brighter. A typical view is that of a tiny jewel of a bird, bright green above and whitish below, and adorned with broad, bright yellow supercilia bulging before the eye, a strong dark eyestripe, and dark crown sides with a sharply defined yellow central stripe. It boasts broad, double yellow wing-bars, white tertial edges and a neat ‘postage stamp’ of a yellow rump. Pallas’s Warblers habitually hover, picking insects off the underside of leaves, and they can hang upside down like a tit, too.
Its call is quiet and easily missed: a soft, slightly finchlike chewit.
Eastern Crowned Warbler
This slightly larger species has an extreme Far Eastern distribution, breeding in Transbaikalia, the Russian Far East, Korea and Japan. It winters in southern Thailand and Malaysia.
The first British record was in 2009, since when a further three have occurred, all in October. There are no Irish records.
It is perhaps most similar to Arctic Warbler, but is brighter green above with narrow double wing-bars, plain tertials, a yellowish wash to the undertail coverts, extensive orange in the lower mandible and, most importantly, a pale central crown stripe, most obvious from behind.
It rarely calls, particularly so during its few British stays, but can utter a strident chiu, a quieter phit phit or a nasal dweee.
Pale-legged Leaf Warbler
Pale-legged Leaf Warbler breeds even farther east than Eastern Crowned Warbler – in the Russian Far East and North Korea – and winters in South-East Asia.
The only confirmed British record was a bird found dead on St Agnes, Scilly, in October 2016, but another example – either of this species or the near-identical Sakhalin Leaf Warbler (breeding in Sakhalin and Japan, and a recent split) – was on Portland, Dorset, in October 2012.
Pale-legged Leaf Warbler is a dark mossy green above, with a contrasting greyish forehead, crown and nape (with no central stripe). There are narrow double wingbars and the tertials are plain. The legs are a very pale pink, but its most notable features might be its neurotic, rather Dusky Warbler-like behaviour and distinctive, highpitched, insistent zink call.