Tree warblers are medium-sized

warbler Various Passeriformes (perching birds) are commonly referred to as warblers. They are not necessarily closely related to one another, but share some characteristics, such as being fairly small, vocal, and insectivorous. Sylvioid warblers T ...

s in the marsh- and tree-warbler family

Acrocephalidae The Acrocephalidae (the reed warblers, marsh- and tree-warblers, or acrocephalid warblers) are a family of oscine passerine birds, in the superfamily Sylvioidea. The species in this family are usually rather large "warblers". Most are rather pl ...

. They are found in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and western

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. Until recently, they were all classified in the single

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'' 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 A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant which eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores we ...

, but will occasionally take

berries A berry is a small, pulpy, and often edible fruit. Typically, berries are juicy, rounded, brightly colored, sweet, sour or tart, and do not have a stone fruit, stone or pit (fruit), pit although many wikt:pip#Etymology 2, pips or seeds may be p ...

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s. The species breeding in temperate regions are mostly strongly migratory.

Taxonomy

All the tree warblers were formerly placed in the "

Old World warbler The Old World warblers are a large group of birds formerly grouped together in the bird family Sylviidae. They are not closely related to the New World warblers. The family held over 400 species in over 70 genera, and were the source of much taxo ...

" family Sylviidae but are now separated in the family

, 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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

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 The British Ornithologists' Union (BOU) aims to encourage the study of birds (ornithology) around the world in order to understand their biology and aid their conservation. The BOU was founded in 1858 by Professor Alfred Newton, Henry Baker Tr ...

retained the genus ''Hippolais'', for all eight species, but in agreement with Sangster, acknowledged that they fell into two groups. The retention of the ''Iduna'' grouping within ''Hippolais'' was done because it was felt that more evidence was needed for its placement, because of low bootstrap values, rather than because of a belief that the status quo was correct – no evidence was put forward to refute the DNA findings. Mark Constantine, in ''The Sound Approach to Birding'', illustrated that there is extensive overlap in song types between species from the two genera, and that vocally, no characters existed which enabled species to be sorted into one genus or the other.

Kenneth Williamson Kenneth Williamson FRSE MBOU (c. 1914 – 14 June 1977) was a British ornithologist who had a strong association with Scotland and with bird migration. Life Williamson was born in Bury, Lancashire. After briefly working as a journalist, Willia ...

and

Hadoram Shirihai Hadoram Shirihai (; born in Israel 1962) is an Israeli ornithologist and writer. Biography Shirihai is the son of Batia and Eli Shirihai. His mother was a schoolteacher, his father was a zoologist in Israel. He grew up in Jerusalem where he beca ...

, in discussing the identification of ''Hippolais'' and ''Acrocephalus'' warblers stressed the similarities between species in the two genera. Colin Bradshaw, in '' British Birds'', has written several articles on morphological similarity between cross-generic species-pairs e.g. eastern olivaceous and Blyth's reed warblers (Bradshaw 2000) and paddyfield and booted warblers (e.g. Bradshaw & Steele 1995, Bradshaw & Steele 1997, the latter a response to Lars Svensson's comments on Bradshaw & Steele 1995). The species are: Genus '' Iduna'' *

Thick-billed warbler The thick-billed warbler (''Arundinax aedon'') breeds in the temperate east Palearctic, from south Siberia to west Mongolia. It is bird migration, migratory, wintering in tropical South Asia and South-east Asia. It is a very rare vagrant to west ...

, ''Iduna aedon'' * Booted warbler, ''Iduna caligata'' * Sykes's warbler, ''Iduna rama'' * Western olivaceous warbler (or isabelline warbler),The name isabelline warbler was first used in volume 11 of the Handbook of the Birds of the World. ''Iduna opaca'' * Eastern olivaceous warbler, ''Iduna pallida'' * Mountain yellow warbler, ''Iduna similis'' * African yellow warbler, ''Iduna natalensis'' Genus '' Hippolais'' * Upcher's warbler, ''Hippolais languida'' * Olive-tree warbler, ''Hippolais olivetorum'' * Melodious warbler, ''Hippolais polyglotta'' *

Icterine warbler The Icterine warbler (''Hippolais icterina'') is an Old World warbler in the tree warbler genus ''Hippolais''. It breeds in mainland Europe except the southwest, where it is replaced by its western counterpart, the melodious warbler. It is bird m ...

, ''Hippolais icterina'' Genus ''Calamonastides'' *

Papyrus yellow warbler The papyrus yellow warbler, papyrus flycatcher-warbler or thin-billed flycatcher-warbler (''Calamonastides gracilirostris'') is a species of tree warbler; formerly, these were placed in the paraphyletic "Old World warblers". It is monotypic in it ...

, ''Calamonastides gracilirostris''

Taxonomy

References

Further reading