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 taxonomic confusion. Two families were split out initially, the cisticolas into Cisticolidae and the kinglets into Regulidae. In the past 20–30 years they have been the subject of much research and many species are now placed into other families, including the Acrocephalidae, Cettiidae, Phylloscopidae, and Megaluridae. 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 family Sylviidae.
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 genera Sylvia and Curruca . 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 primarily insectivorous, although many will also eat soft fruit, nectar, or tiny seeds. [1]
The majority of species are monogamous 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 small insectivorous bird species in nearly 50 genera, a huge family, with few clear patterns of relationships recognisable. Though not as diverse as the Timaliidae (Old World babblers; another "wastebin taxon" containing more thrush-like forms), the frontiers were much blurred. The largely tropical warbler family Cisticolidae was at that time traditionally included in the Sylviidae. The kinglets, now a small genus in a monotypic family Regulidae, were also sometimes placed in this family, including by the influential List of Recent Holarctic Bird Species , [3] . The American Ornithologists' Union then also included the gnatcatchers, as subfamily Polioptilinae, in the Sylviidae. [4]
Sibley & Ahlquist (1990) united the "Old World warblers" with the babblers and other taxa in a superfamily Sylvioidea as a result of DNA–DNA hybridisation studies. This demonstrated that the Sylviidae as initially defined was a form taxon which collected unrelated songbirds. Consequently, the monophyly of the individual "songster" lineages themselves was increasingly being questioned.
More recently, analysis of DNA 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 the parrotbills were left out entirely (e.g. Ericson & Johansson 2003, Barker et al. 2004). These could only confirm that the Cisticolidae were indeed distinct, and suggested that bulbuls (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) using mtDNA cytochrome b and 12S/16S rRNA data indicated that the Sylviidae and Old World babblers were not reciprocally monophyletic to each other. Moreover, Sylvia, the type genus of the Sylviidae, turned out to be closer to taxa such as the yellow-eyed babbler (Chrysomma sinense, traditionally held to be an atypical timaliid) and the wrentit (Chamaea fasciata), an enigmatic species generally held to be the only American Old World babbler. The parrotbills Paradoxornithidae (roughly, "puzzling birds") of then unclear affiliations also were part of what apparently was a well distinctive clade.
Cibois suggested that the Sylviidae should officially be suppressed by the ICZN as a taxon and the genus Sylvia 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 Beresford et al. (2005) and Alström et 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, and Megaluridae, this last turning out to be a synonym of the older-published Locustellidae) to better reflect the evolutionary history of the sylvioid group.
Typical warblers (or sylviid 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 or acrocephalid 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 into Pacific, some in Africa.
See Cibois et al. (2001)
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 the Indian Ocean.
The black-capped donacobius Donacobius atricapillus, which was long considered an aberrant wren or mockingbird is apparently quite closely related, and is the only South American species in the superfamily Sylvioidea.
Typical bush warblers and relatives or cettiid 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.
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 of Sylvioidea families listed above. Those in the Australian-Pacific region are probably Megaluridae. These taxa are listed in the sequence used in recent years.
Entirely unrelated songbirds hitherto placed in Sylviidae
The typical warblers are small birds belonging to the genus Sylvia in the "Old World warbler" family Sylviidae.
The Old World babblers or Timaliidae, are a family of mostly Old World passerine birds. They are rather diverse in size and coloration, but are characterised by soft, fluffy plumage. These are birds of tropical areas, with the greatest variety in Southeast Asia and the Indian subcontinent. The timaliids are one of two unrelated groups of birds known as babblers, the other being the Australasian babblers of the family Pomatostomidae.
The wrentit is a small bird that lives in chaparral, oak woodlands, and bushland on the western coast of North America. It is the only species in the genus Chamaea.
The ashy-throated parrotbill is a parrotbill. In old sources, it may be called Alphonse's crow-tit; though superficially resembling a tit it is not a member of the Paridae. The native range of this species extends from south-west China to northern Vietnam, and it might have become naturalised in one area in Italy.
Cincloramphus is a genus of birds in the grassbird family Locustellidae.
Macrosphenus is a genus of African warblers, formerly placed in the family Sylviidae. It is one of two genera in that family known as longbills.
The New Caledonia thicketbird or New Caledonia grassbird, is a bird species. Previously placed in the "Old World warbler" family Sylviidae, it does not seem to be a close relative of the typical warblers; probably it belongs in the grass warbler family Locustellidae. This species is endemic to New Caledonia.
The red-capped crombec is a species of African warbler, formerly placed in the family Sylviidae.
Cettiidae is a newly validated family of small insectivorous songbirds ("warblers"), formerly placed in the Old World warbler "wastebin" assemblage. It contains the typical bush warblers (Cettia) and their relatives. As a common name, cettiid warblers is usually used.
Locustellidae is a newly recognized family of small insectivorous songbirds ("warblers"), formerly placed in the Old World warbler "wastebin" family. It contains the grass warblers, grassbirds, and the Bradypterus "bush warblers". These birds occur mainly in Eurasia, Africa, and the Australian region. The family name is sometimes given as Megaluridae, but Locustellidae has priority.
Pnoepyga is a genus of passerines endemic to southern and southeastern Asia. Its members are known as cupwings or wren-babblers. The genus contains four species. The genus has long been placed in the babbler family Timaliidae. A 2009 study of the DNA of the families Timaliidae and the Old World warblers (Sylviidae) found no support for the placement of the genus in either family, prompting the authors to erect a new monogeneric family, the Pnoepygidae.
Sylvioidea is a superfamily of passerine birds, one of at least three major clades within the Passerida along with the Muscicapoidea and Passeroidea. It contains about 1300 species including the Old World warblers, Old World babblers, swallows, larks and bulbuls. Members of the clade are found worldwide, but fewer species are present in the Americas.
Alcippe is a genus of passerine birds in the monotypic family Alcippeidae. The genus once included many other fulvettas and was previously placed in families Pellorneidae or Timaliidae.
The African warblers are a newly erected family Macrosphenidae, of African songbirds. Most of the species were formerly placed in the Old World warbler family Sylviidae, although one species, the rockrunner, was placed in the babbler family, Timaliidae. A series of molecular studies of the Old World warblers and other bird families in the superfamily Sylvioidea found that the African warblers were not part of Sylviidae but were instead an early (basal) offshoot of the entire clade Sylvioidea. Some taxonomic authorities place the entire family Hyliidae here.
The jungle babblers are a family, Pellorneidae, of mostly Old World passerine birds belonging to the superfamily Sylvioidea. They are quite diverse in size and coloration, and usually characterised by soft, fluffy plumage and a tail on average the length of their body, or longer. These birds are found in tropical zones, with the greatest biodiversity in Southeast Asia and the Indian subcontinent.