TheOld World warblers are a large group of birds formerly grouped together in the bird familySylviidae. They are not closely related to theNew World warblers. 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 cisticolas intoCisticolidae and the kinglets intoRegulidae. In the past 20–30 years they have been the subject of much research and many species are now placed into other families, including theAcrocephalidae,Cettiidae,Phylloscopidae, andMegaluridae. In addition some species have been moved into existing families or have not yet had their placement fully resolved. Only a small number of warblers, in just two genera, are now retained in the familySylviidae.
Most Old World warblers are of generally undistinguished appearance, though some species are boldly marked. The sexes are often identical, but may be clearly distinct, notably in the generaSylvia andCurruca. They are of small to medium size, varying from 9 to 20 centimetres in length, with a slender, finely pointed bill. Almost all species are primarilyinsectivorous, although many will also eat soft fruit, nectar, or tiny seeds.[1]
The majority of species aremonogamous and build simple,cup-shaped nests in dense vegetation. They lay between two and six eggs per clutch, depending on species. Both parents typically help in raising the young, which are able to fly at around two weeks of age.[2]
In the late 20th century, the Sylviidae were thought to unite nearly 300 smallinsectivorous birdspecies in nearly 50genera, a huge family, with few clear patterns of relationships recognisable. Though not as diverse as theTimaliidae (Old World babblers; another "wastebin taxon" containing more thrush-like forms), the frontiers were much blurred. The largely tropical warbler familyCisticolidae was at that time traditionally included in the Sylviidae. Thekinglets, now a small genus in amonotypic family Regulidae, were also sometimes placed in this family, including by the influentialList of Recent Holarctic Bird Species,[3]. TheAmerican Ornithologists' Union then also included thegnatcatchers, as subfamily Polioptilinae, in the Sylviidae.[4]
Sibley & Ahlquist (1990) united the "Old World warblers" with the babblers and othertaxa in asuperfamilySylvioidea as a result ofDNA–DNA hybridisation studies. This demonstrated that the Sylviidae as initially defined was aform taxon which collected unrelated songbirds. Consequently, themonophyly of the individual "songster" lineages themselves was increasingly being questioned.
More recently, analysis ofDNA sequence data has provided information on the Sylvioidea. Usually, the scope of the clade was underestimated and only one or two specimens were sampled for each presumed "family". Minor or little-known groups such as theparrotbills were left out entirely (e.g. Ericson & Johansson 2003, Barkeret al. 2004). These could only confirm that the Cisticolidae were indeed distinct, and suggested thatbulbuls (Pycnonotidae) were apparently the closest relatives of a group containing Sylviidae, Timaliidae, cisticolids and white-eyes.
In 2003, a study of Timaliidae relationships (Cibois 2003a) usingmtDNAcytochromeb and12S/16S rRNA data indicated that the Sylviidae and Old World babblers were not reciprocally monophyletic to each other. Moreover,Sylvia, thetype genus of the Sylviidae, turned out to be closer to taxa such as theyellow-eyed babbler (Chrysomma sinense, traditionally held to be an atypical timaliid) and thewrentit (Chamaea fasciata), an enigmatic species generally held to be the onlyAmerican Old World babbler. The parrotbillsParadoxornithidae (roughly, "puzzling birds") of then unclear affiliations also were part of what apparently was a well distinctiveclade.
Cibois suggested that the Sylviidae should officially be suppressed by theICZN as a taxon and the genusSylvia merged into the Timaliidae (Cibois 2003b), but this was rejected. Clearly, the sheer extent of the groups concerned made it necessary to study a wide range of taxa. This was begun by Beresfordet al. (2005) and Alströmet al. (2006). They determined that the late-20th-century Sylviidae united at least four, but probably as many as seven major distinct lineages. The authors propose the creation of several new families (Phylloscopidae,Cettiidae,Acrocephalidae, andMegaluridae, this last turning out to be a synonym of the older-publishedLocustellidae) to better reflect theevolutionary history of the sylvioid group.
Typical warblers (orsylviid warblers). A fairly diverse group of smallish taxa with longish tails, now containing 33 species in two genera. Mostly in Europe and the Mediterranean region, with a few extending to central Asia and in tropical Africa.
Marsh and tree warblers oracrocephalid warblers. Usually rather large "warblers", most are olivaceous brown above with much yellow to beige below. Usually in open woodland, reed beds or tall grass. Mainly southern Asia to western Europe and surroundings ranging far intoPacific, some in Africa.
GenusAcrocephalus – marsh warblers (about 38 living species, 5 recentlyextinct)
Grass warblers and allies. Mid-sized and usually long-tailed species; sometimes strongly patterned but generally very drab in overall colouration. Often forage in dense low vegetation. Old World and into Australian region, centred on theIndian Ocean.
GenusBradypterus – megalurid warblers (12 species, including the forner genusDromaeocercus)
GenusLocustella – grass warblers (more than 20 species)
Theblack-capped donacobiusDonacobius atricapillus, which was long considered an aberrantwren ormockingbird is apparently quite closely related, and is the only South American species in the superfamily Sylvioidea.
Typical bush warblers and relatives orcettiid warblers. Another group of generally very drab species, tend to be smaller and shorter-tailed than Megaluridae. Usually frequent shrubland and undergrowth. Continental Asia, and surrounding regions, ranging into Africa and southern Europe.
GenusPholidornis – formerly inRemizidae; tentatively placed here
Leaf warblers. A group variable in size, generally dull to vivid green above and whitish or yellow below, or more subdued with greyish-green to greyish-brown plumage. Catch food on the wing fairly often. Eurasia, ranging into Wallacea and Africa.
African warblers. Also "Sphenoeacus group". An assemblage of usually species-poor and apparently rather ancient "odd warblers" from Africa.Ecomorphologically quite variable. Monophyly requires confirmation.
Taxa that have not been studied. Most are likely to belong to one ofSylvioidea families listed above. Those in the Australian-Pacific region are probablyMegaluridae. These taxa are listed in the sequence used in recent years.
GenusStenostira – Together with some "odd flycatchers", they form the new familyStenostiridae. They are closely related toParidae (Beresfordet al. 2005)
^Sefc, K. M.; Payne, R. B.; Sorenson, M. D. (2003). "Phylogenetic relationships of African sunbird-like warblers: Moho Hypergerus atriceps, Green Hylia Hylia prasina and Tit-hylia Pholidornis rushiae".Ostrich.74 (1–2):8–17.doi:10.2989/00306520309485365.S2CID86085338.
^Johansson, U.S.; Fjeldså, J.; Bowie, R.C.K. (2008). "Phylogenetic relationships within Passerida (Aves: Passeriformes): A review and a new molecular phylogeny based on three nuclear intron markers".Mol. Phylogenet. Evol.48 (3):858–876.doi:10.1016/j.ympev.2008.05.029.PMID18619860.
^Fuchs, J.; Fjeldså, J.; Bowie, R. C. K.; Voelker, G.; Pasquet, E. (2006). "The African warbler genus Hyliota as a lost lineage in the oscine songbird tree: Molecular support for an African origin of the Passerida".Mol. Phylogenet. Evol.39 (1):186–197.doi:10.1016/j.ympev.2005.07.020.PMID16182572.
Alström, P.; Ericson, P. G. P.; Olsson, U.; Sundberg, P. (2006). "Phylogeny and classification of the avian superfamily Sylvioidea".Molecular Phylogenetics and Evolution.38 (2):381–397.doi:10.1016/j.ympev.2005.05.015.PMID16054402.
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