Pallas's leaf warbler

For the Locustella warbler species occasionally referred to as Pallas's warbler, see Pallas's grasshopper warbler.

Pallas's leaf warbler
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Phylloscopidae
Genus:	Phylloscopus
Species:	P. proregulus
Binomial name
Phylloscopus proregulus (Pallas, 1811)

The Pallas's leaf warbler or Pallas's warbler (Phylloscopus proregulus) is a leaf warbler which breeds in southern Siberia (from Novosibirsk Oblast east to Magadan Oblast), northern Mongolia, and northeastern China. It is strongly migratory and winters mainly in subtropical southern China and northeastern Indochina, but also in small numbers in western Europe.

It is one of the smallest warblers; at 9–10 cm long and 4–7 g weight it is slightly smaller than a yellow-browed warbler and barely any larger than a goldcrest. Overall, it has greenish upperparts and white underparts, but is very striking, with prominent pale yellow wingbars on the tips of the greater and median coverts, bold yellow supercilia and central crown stripe, and a lemon-yellow rump. It is not shy, but its unobtrusive arboreal lifestyle makes it difficult to observe. It is constantly in motion, and often hovers briefly like a Goldcrest. Its song is a medley of whistles, with some phrases reminiscent of a canary ; the call is a short chweey.

It breeds in coniferous taiga and mountain forests, and like most warblers, is insectivorous. The nest is built in a tree, usually next to the trunk at 0.5–10 m above ground; four to six eggs are laid, hatching after 12–13 days, with the chicks fledging when 12–14 days old.

In winter, it uses a slightly broader range of habitats, including broadleaf forest and scrub as well as conifers. Although the vast majority winter in southern China south of the Yangtze River (where they are present from October to April), small numbers also regularly winter in western Europe. These arrive in Great Britain in October to November after a 5,000 km migration from the western end of the breeding range, about the same distance that they would need to fly to reach the normal wintering areas in southern China. Exact numbers in this population are unknown, but up to 300 per year have been found arriving in Great Britain in autumn; given their unobtrusive behaviour, this is probably only a fraction of the total. In the past widely considered to be vagrants, these birds are now thought to be undertaking a normal regular migration, taking advantage of the mild oceanic climate winters on the western fringes of Europe for wintering.

Taxonomy

Pallas's leaf warbler is named after the German zoologist Peter Simon Pallas, who discovered it on the Ingoda River in Siberia in 1811; the species name proregulus derives from its similar size to the goldcrest Regulus regulus. In the past, it was treated as a complex of several subspecies; apart from the nominate subspecies breeding in northern Asia, two to four other subspecies were accepted, breeding much further south at high altitudes in the Sino-Himalayan mountain system from the western Himalaya east to western China (Yunnan north to Gansu and Hebei). Even though they differ only slightly in plumage, they are very distinct vocally with both song and calls differing. Genetic analysis has also shown them to be distinct, and they are now treated as separate species:

• Lemon-rumped warbler Phylloscopus chloronotus. Himalaya, SW China. Three subspecies, P. c. chloronotus, P. c. forresti, P. c. simlaensis.
• Gansu leaf warbler Phylloscopus kansuensis. Central western China. Monotypic.
• Chinese leaf warbler Phylloscopus yunnanensis (syn. P. sichuanensis). Western China. Monotypic.

Of these, Phylloscopus chloronotus forresti is possibly also a separate species, but further analysis is required to confirm this. Gansu leaf warbler and Chinese leaf warbler overlap in breeding range in southern Gansu, but are separated ecologically, with Gansu leaf warbler using taller forest habitats and Chinese leaf warbler in lower, often scrubby habitats.