Leaf warblers are small insectivorous passerine birds belonging to the genus Phylloscopus. The genus was introduced by the German zoologist Friedrich Boie in 1826. The name Phylloscopus is from Ancient Greek phullon, 'leaf', and skopos, 'seeker' (from skopeo, 'to watch'). Leaf warblers were formerly included in the Old World warbler family but are now considered to belong to the family Phylloscopidae, introduced in 2006. The family originally included the genus Seicercus, but all species have been moved to Phylloscopus in the most recent classification. Leaf warblers are active, constantly moving, often flicking their wings as they glean the foliage for insects along the branches of trees and bushes. They forage at various levels within forests, from the top canopy to the understorey. Most of the species are markedly territorial both in their summer and winter quarters. Most are greenish or brownish above and off-white or yellowish below. Compared to some other 'warblers', their songs are very simple. Species breeding in temperate regions are usually strongly migratory. The species are of various sizes, often green-plumaged above and yellow below, or more subdued with greyish-green to greyish-brown colours, varying little or not at all with the seasons. The tails are not very long and contain 12 feathers (unlike the similar Abroscopus species, which have 10 tail feathers). Many species are more easily identified by their distinctive songs than their dull plumage. Its members occur in Eurasia, ranging into Wallacea and Africa with one species, the Arctic warbler, breeding as far east as Alaska). Many of the species breed at temperate and high latitudes in Eurasia and migrate substantial distances to winter in southeastern Asia, India, or Africa. One example is Tickell's leaf warbler, which breeds in scrub at high elevation in the Himalayas and on the Tibetan Plateau and then moves down-slope and south to winter in the Himalayan foothills of India and Burma. Most live in forest and scrub and many are canopy or sub-canopy dwellers. The family Phylloscopidae comprises many small tree-loving warbler species and feed by gleaning insects from leaves or catching food on the wing. The genus includes eleven species that were formerly placed in the genus Seicercus, but a 2018 molecular phylogeny study indicated that the genus Seicercus is a synonym of Phylloscopus, leaving the family Phylloscopidae with a single genus, Phylloscopus. The genus contains 77 species: