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 Th ...

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 p ...

. They are found in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

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

and western

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an ...

. Until recently, they were all classified in the single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

Hippolais ''Hippolais'' is a genus of tree warbler in the family Acrocephalidae. It is sometimes associated with the genus '' Iduna''. The genus name ''Hippolais'' is from Ancient Greek ''hupolais'', as misspelt by Linnaeus. It referred to a small bird ...

''. 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 that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...

, 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 or pit, although many pips or seeds may be present. Common examples are strawberries, rasp ...

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...

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

Taxonomy

All the tree warblers were formerly placed in the "

Old World warbler Old World warblers are a large group of birds formerly grouped together in the bird family Sylviidae. The family held over 400 species in over 70 genera, and were the source of much taxonomic confusion. Two families were split out initially, the ci ...

" 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 In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

with respect to ''Acrocephalus''. DNA studies, e.g. Leisler et al. (1997), interpreted by

George Sangster George Sangster is a Dutch ornithologist Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to them." Several aspects of ornithology differ from related discipline ...

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") and around the world, in order to understand their biology and to aid their conservation. The BOU was founded in 1858 by Professor Alfred Newton, Henry ...

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 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 becam ...

, 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 migratory, wintering in tropical South Asia and South-east Asia. It is a very rare vagrant to western Europe. Th ...

, ''Iduna aedon'' *

Booted warbler The booted warbler (''Iduna caligata'') is an Old World warbler in the tree warbler group. It was formerly considered to be conspecific with Sykes's warbler, but the two are now usually both afforded species status. Booted warbler itself breeds ...

, ''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 The mountain yellow warbler or mountain flycatcher-warbler (''Iduna similis'') is a species of Acrocephalidae warbler; formerly, these were placed in the paraphyletic "Old World warblers". Range and habitat It is found in Burundi, DRC, Kenya, Mal ...

, ''Iduna similis'' *

African yellow warbler The African yellow warbler (''Iduna natalensis''), also known as Natal yellow warbler, dark-capped yellow warbler or yellow flycatcher-warbler, is a species of Acrocephalidae warblers; formerly, these were placed in the paraphyletic "Old World wa ...

, ''Iduna natalensis'' Genus ''

'' * Upcher's warbler, ''Hippolais languida'' *

Olive-tree warbler The olive-tree warbler (''Hippolais olivetorum'') is an Old World warbler in the tree warbler genus '' Hippolais''. It breeds in southeast Europe and the Near East. It is migratory, wintering in eastern and southern Africa, from Kenya south to ...

, ''Hippolais olivetorum'' *

Melodious warbler The melodious warbler (''Hippolais polyglotta'') is an Old World warbler in the tree warbler genus ''Hippolais''. It breeds in southwest Europe and northwest Africa. It is migratory, wintering in sub-Saharan Africa. This small passerine bi ...

, ''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 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