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 cisticolas into Cisticolidae and the kinglets into Regulidae. In the past ten 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. A smaller family of warblers, together with some babblers formerly placed in the family Timaliidae and the parrotbills, are retained in a much smaller family Sylviidae.

Most Old World warblers are of generally undistinguished appearance, though some Asian species are boldly marked. The sexes are often identical, but may be clearly distinct, notably in the genus Sylvia. They are of small to medium size, varying from 9 to 16 centimetres in length, with a small, finely pointed bill. Almost all species are primarily insectivorous, although some will also eat fruit, nectar, or tiny seeds.

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.

In the late 20th century, the Sylviidae were thought to unite nearly 300 small insectivorous bird species in nearly 50 genera. They had themselves been split out of the Muscicapidae. The latter family had for most of its existence served as perhaps the ultimate wastebin taxon on the history of ornithology. By the early 20th century, about every insectivorous Old World "songster" known to science had at one point been placed therein, and most continued to be so.

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