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 Continent#Subcontinents, subcontinent of Eurasia ...

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 area ...

. Until recently, they were all classified in the single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 men ...

''. 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 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, raspb ...

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 angiospe ...

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. He specialises in taxonomy and has written many articles on this subject for the magazines Dutch Birding ''Dutch Birding'', originally subtitled ''Journal of the Dutch Birding Association'', and curren ...

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. 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, Wil ...

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, ''Iduna aedon'' * Booted warbler, ''Iduna caligata'' *

Sykes's warbler Sykes's warbler (''Iduna rama'') is an Old World warbler in the tree warbler family. It was formerly considered a subspecies of the booted warbler, but is now considered a full species. Its breeding range is from northeast Arabia to Turkestan, ...

, ''Iduna rama'' *

Western olivaceous warbler The western olivaceous warbler (''Iduna opaca''), also known as isabelline warbler, is a "warbler", formerly placed in the Old World warblers when these were a paraphyletic wastebin taxon. It is now considered a member of the acrocephaline warbl ...

(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 The eastern olivaceous warbler (''Iduna pallida'') is a small passerine bird with drab plumage tones, that is native to the Old World. For the most part it breeds in southeastern Europe, the Middle East and adjacent western Asia, and winters in t ...

, ''Iduna pallida'' * Mountain yellow warbler, ''Iduna similis'' * African yellow warbler, ''Iduna natalensis'' Genus ''

'' *

Upcher's warbler Upcher's warbler (''Hippolais languida'') is an Old World warbler in the tree warbler genus ''Hippolais''. It breeds in an area from Turkey south and east to Pakistan. It is migratory, wintering in eastern Africa, from Eritrea and Somalia south ...

, ''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 bird is ...

, ''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 migr ...

, ''Hippolais icterina'' Genus ''Calamonastides'' * Papyrus yellow warbler, ''Calamonastides gracilirostris''

Taxonomy

References

Further reading