Tree warbler

Tree warblers
Several Hippolais species
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Acrocephalidae

Tree warblers are medium-sized warblers in the marsh- and tree-warbler family Acrocephalidae. They are found in Europe, Africa and western Asia. Until recently, they were all classified in the single genus Hippolais.

These warblers are associated with trees, though normally in fairly open woodland rather than tight plantations. Compared with the closely related Acrocephalus species, tree warblers have squarer tails and broader bill-bases. Most are unstreaked greenish or brownish above and cream or white below. They are insectivorous, but will occasionally take berries or seeds. The species breeding in temperate regions are mostly strongly migratory.

All the tree warblers were formerly placed in the "Old World warbler" family Sylviidae but are now separated in the family Acrocephalidae, along with the marsh warblers, Acrocephalus, and some related species.

Considerable evidence, much of it summarised in Parkin et al. (2004), suggests that the genus Hippolais is paraphyletic with respect to Acrocephalus. DNA studies, e.g. Leisler et al. (1997), interpreted by George Sangster in 1997, indicated that the olivaceous and booted/Sykes's warbler grouping (the subgenus Iduna) are more closely related to Acrocephalus species than they are to icterine and melodious warblers and as a result the Dutch Committee on Avian Systematics (CSNA) has moved these four species into Acrocephalus. A subsequent review by the British Ornithologists' Union Records Committee retained the genus Hippolais, for all eight species, but in agreement with Sangster, acknowledged that they fell into two groups.

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