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.
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, 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:
- Thick-billed Warbler, Iduna aedon
- Booted Warbler, Iduna caligata
- Sykes's Warbler, Iduna rama
- Western Olivaceous Warbler (or Isabelline Warbler), Iduna opaca
- Eastern Olivaceous Warbler, Iduna pallida
- Mountain Yellow Warbler, Iduna similis
- African Yellow Warbler, Iduna natalensis
- Upcher's Warbler, Hippolais languida
- Olive-tree Warbler, Hippolais olivetorum
- Melodious Warbler, Hippolais polyglotta
- Icterine Warbler, Hippolais icterina
- Papyrus Yellow Warbler, Calamonastides gracilirostris
- Del Hoyo, J.; Elliot, A.; Christie D., ed. (2006). Handbook of the Birds of the World. Volume 11: Old World Flycatchers to Old World Warblers. Lynx Edicions. ISBN 84-96553-06-X.
- Mullarney, K.; Svensson, L.; Zetterström, D.; Grant, P. J. (1999). Collins Bird Guide. HarperCollins. ISBN 0-00-219728-6.
- Parkin, David T.; Collinson, Martin; J. Helbig, Andreas; Knox, Alan G.; Sangster, George; Svensson, Lars (2004). "Species limits in Acrocephalus and Hippolais warblers from the Western Palearctic". British Birds 97 (6): 276–299.
- Leisler, B.; Heidrich, P.; Schulze-Hagen, K. M.; Wink, M. (1997). "Taxonomy and phylogeny of reed warblers (genus Acrocephalus) based on mtDNA sequences and morphology". J. Ornithol. 138 (4): 469–496. doi:10.1007/BF01651381.
- Sangster, George (1997). "Trends in Systematics – Acrocephalus and Hippolais relationships: shaking the tree". Dutch Birding 19 (6): 294–300.
- Sangster, George; Hazevoet, Cornelius J.; van den Berg, Arnoud B.; Roselaar, C. S. (1998). "Dutch avifaunal list: species concepts, taxonomic instability, and taxonomic changes in 1998". Dutch Birding 20 (1): 22–32.
- Knox, Alan G.; Collinson, Martin; Helbig, Andreas J.; Parkin, David T.; Sangster, George (2002). "Taxonomic recommendations for British birds". Ibis 144 (4): 707–710. doi:10.1046/j.1474-919X.2002.00110.x.
- Helbig, A. J.; Seibold, I. (1999). "Molecular phylogeny of Palearctic-African Acrocephalus and Hippolais warblers (Aves: Sylviidae)". Mol. Phyl. Evol. 11 (2): 246–260. doi:10.1006/mpev.1998.0571. PMID 10191069.
- Constantine, Mark; The Sound Approach (2006). The Sound Approach to birding: a guide to understanding bird sound (1st. ed.). Dorset, England: The Sound Approach. pp. 142–148. ISBN 90-810933-1-2.
- Williamson, K. (1968). Identification for ringers 1. The genera Cettia, Locustella, Acrocephalus and Hippolais.
- Harris, A.; Shirihai, H.; Christie, D. The Macmillan birder's guide to European and Middle Eastern birds.
- Bradshaw, Colin (2000). "Separating Acrocephalus and Hippolais warblers". British Birds 93 (6): 277.
- Bradshaw, Colin; Steele, Jimmy (1995). "Mystery photographs 195". British Birds 88 (11): 561–564.
- Bradshaw, Colin; Steele, Jimmy (1997). "Mystery warblers in Tselinograd". British Birds 90 (4): 155–158.
- Svensson, Lars (1997). "Mystery warblers in Tselinograd". British Birds 90 (4): 152–154.
- The name Isabelline Warbler was first used in volume 11 of the Handbook of the Birds of the World.
The species in this family are usually rather large "warblers". Most are rather plain olivaceous brown above with much yellow to beige below. They are usually found in open woodland, reedbeds or tall grass. The family occurs mostly in southern to western Eurasia and surroundings, but also ranging far into Pacific, with some species in Africa.
Marsh-warblers. About 35 species; para- or polyphyletic.
- Moustached warbler, Acrocephalus melanopogon
- Aquatic warbler, Acrocephalus paludicola
- Sedge warbler, Acrocephalus schoenobaenus
- Speckled reed warbler, Acrocephalus sorghophilus
- Black-browed reed warbler, Acrocephalus bistrigiceps
- Paddyfield warbler, Acrocephalus agricola
- Manchurian reed warbler, Acrocephalus tangorum
- Blunt-winged warbler, Acrocephalus concinens
- Eurasian reed warbler, Acrocephalus scirpaceus
- Caspian reed warbler, Acrocephalus (scirpaceus) fuscus
- Mangrove reed warbler, Acrocephalus (scirpaceus) avicenniae
- African reed warbler, Acrocephalus baeticatus
- Blyth's reed warbler, Acrocephalus dumetorum
- Marsh warbler, Acrocephalus palustris
- Great reed warbler, Acrocephalus arundinaceus
- Oriental reed warbler, Acrocephalus orientalis
- Clamorous reed warbler, Acrocephalus stentoreus
- Large-billed reed warbler, Acrocephalus orinus
- Basra reed warbler, Acrocephalus griseldis
- Australian reed warbler, Acrocephalus australis
- Nightingale reed warbler, Acrocephalus luscinia
- Saipan reed warbler, Acrocephalus hiwae
- Aguiguan reed warbler, Acrocephalus nijoi - extinct (c.1997)
- Mangareva reed warbler, Acrocephalus astrolabii - extinct (mid-19th century?)
- Pagan reed warbler, Acrocephalus yamashinae extinct (1970s)
- Carolinian reed warbler, Acrocephalus syrinx
- Nauru reed warbler, Acrocephalus rehsei
- Millerbird, Acrocephalus familiaris
- Bokikokiko, Acrocephalus aequinoctialis
- Tahiti reed warbler, Acrocephalus caffer
- Garrett's reed warbler, Acrocephalus garretti - extinct (19th century?)
- Raiatea reed warbler, Acrocephalus caffer musae - extinct (19th century?)
- Tuamotu reed warbler, Acrocephalus atyphus
- Rimatara reed warbler, Acrocephalus rimatarae
- Pitcairn reed warbler, Acrocephalus vaughani
- Henderson reed warbler, Acrocephalus taiti
- Northern Marquesan reed warbler, Acrocephalus percernis
- Southern Marquesan reed warbler, Acrocephalus mendanae
- Cook reed warbler, Acrocephalus kerearako
- Greater swamp warbler, Acrocephalus rufescens
- Cape Verde warbler, Acrocephalus brevipennis
- Lesser swamp warbler, Acrocephalus gracilirostris
- Madagascar swamp warbler, Acrocephalus newtoni
- Rodrigues warbler, Acrocephalus rodericanus
- Seychelles warbler, Acrocephalus sechellensis
- Thick-billed warbler, Iduna aedon
- Booted warbler, Iduna caligata
- Sykes's warbler, Iduna rama
- Eastern olivaceous warbler, Iduna pallida
- Western olivaceous warbler, Iduna opaca
- African yellow warbler, Iduna natalensis
- Mountain yellow warbler, Iduna similis
- Upcher's warbler, Hippolais languida
- Olive-tree warbler, Hippolais olivetorum
- Melodious warbler, Hippolais polyglotta
- Icterine warbler, Hippolais icterina
- Papyrus yellow warbler, Calamonastides gracilirostris
Brush warblers. 5 living species, 1 recently extinct.
- Aldabra brush warbler, Nesillas aldabrana (extinct: c.1984)
- Anjouan brush warbler, Nesillas longicaudata
- Malagasy brush warbler, Nesillas typica
- Grand Comoro brush warbler, Nesillas brevicaudata
- Moheli brush warbler, Nesillas mariae
- Subdesert brush warbler, Nesillas lantzii
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