Hume's Leaf Warbler - Ecology and Evolution

Ecology and Evolution

This is a common bird of mountain woodlands at altitudes of up to 3,500m ASL. It occurs from the Hindu Kush and Karakoram east and north to the Tien Shan in China and the Altay Mountains in Mongolia. The completely allopatric subspecies mandellii (Mandell's Leaf Warbler or Eastern Hume's Warbler) – sometimes separated as a full species, in which case the nominate subspecies is called Western Hume's Warbler – occurs on the eastern Tibetan Plateau. Both populations migrate over the Himalayas to winter in India and adjacent regions. The species has also been recorded in the Kutch region.

Particularly on autumn migration, this tiny warbler is prone to vagrancy as far as western Europe, despite a 3,000 km distance from its breeding grounds. It is a rare vagrant in late autumn and winter in Great Britain. Non-breeding adults may stray around a lot in summer, when Mandell's Leaf Warblers are fairly common summer visitors to subtropical and temperate montane humid forests of Bhutan, around 2,000-3,500 m ASL and dominated by Bhutan Fir (Abies densa) or by Himalayan Hemlock (Tsuga dumosa) and rhododendrons, though the subspecies is not a regular breeder in that country.

This bird is not shy, although its arboreal lifestyle and cryptic colours make it difficult to observe. It is constantly in motion. Like most "Old World warblers", this small passerine is insectivorous. The nest is built on the ground.

A common species in most of its wide range, Hume's Leaf-warbler is not considered threatened by the IUCN.

It was recently split from the Yellow-browed Warbler (Phylloscopus inornatus), based on differences in morphology, bioacoustics, and molecular characters. The Western Hume's Leaf Warbler's range overlaps with that of the Yellow-browed Warbler in the western Sayan Mountains, but the species apparently do not hybridize. The divergence between the two species has been tentatively estimated at roughly 2,5 million years ago (Ma), and that between P. h. humei and P. h. mandelli at about 1 mya.