(Sylviidae)
Class: Aves
Order: Passeriformes
Suborder: Passeri (Oscines)
Family: Sylviidae
Thumbnail description
Very small to medium-sized, often dull-colored, songbirds with thin, pointed bills
Size
3.1–9.8 in (8–25 cm); .1–2 oz (4–56 g)
Number of genera, species
60 genera; 350–391 species
Habitat
Highly varied. Largely arboreal, but many species inhabit wetlands, grasslands, thickets, scrub, and riparian zones
Conservation status
Endangered: 10 species; Critically Endangered: 3 species; Vulnerable: 29 species; Near Threatened: 13 species; Data Deficient: 9 species
Distribution
Subfamily Sylviinae: Palearctic region, Africa, Asia, Australasia, Oceania. Two genera, Regulus and Phylloscopus, reach Nearctic. Subfamily Polioptilinae: New World, from South America to the northern United States.
Evolution and systematics
The taxonomy of the Passeri, the suborder of oscine passerines (the songbirds) that contains the Sylviidae (Old World warblers), has long been debated. Much of the controversy focuses on the delineation of the apparently closely related families Muscicapidae, Turdidae, Timaliidae, and Sylviidae. Currently available molecular data suggest that widely used, traditional family classifications do not represent the evolutionary history of this large and complex group of birds. Sibley and Ahlquist place the Sylviidae within a large superfamily, the Sylvioidea. This superfamily also contains members of the following traditional families: Sittidae (nuthatches), Certhiidae (creepers), Troglodytidae (wrens), Paridae (tits), Aegithalidae (long-tailed tits), Hirundinidae (swallows), Pycnonotidae (bulbuls), Zosteropidae (whiteeyes), and Timaliidae (babblers). The molecular data do not support the long-held belief that the Sylviidae are closely related to the Turdidae (thrushes) and the Muscicapidae (Old World flycatchers), for these two families fall into a separate superfamily, the Muscicapoidea. The data do, however, support the inclusion of some of the babblers (Timaliinae) and laughing thrushes (genus Garrulax) in the Sylviidae family.
The classification used in the present work is based upon the traditional definition of the Sylviidae. The genera may be divided into six groups, based on molecular evidence of their taxonomic affiliation. The first of these are the gnatcatchers and gnatwrens (Polioptila, Microbates, and Ramphocaenus), which comprise the Sylviid subfamily Polioptilinae, but are placed by Sibley and Ahlquist within an expanded Certhiidae, including both creepers and wrens. The remaining five groups are considered to be within the sylviid subfamily Sylviinae. These are: (1) the kinglets (Regulus), regarded as a separate family by Sibley and Ahlquist and others; (2) the cisticolas and allies (Cisticola, Prinia, Apalis, Camaroptera), and other allied genera, a distinct group that Sibley and Ahlquist regard as a separate family, and most authors regard as a subfamily, Cisticolinae, of the Sylviidae; (3) the Sylvia warblers (Sylvia, Parisoma), a group that, according to Sibley and Ahlquist, is more closely related to the timaliine babblers than to traditional sylviids; (4) the grassbirds and allies (Megalurus, Bowdleria, Cincloramphus, Megalurulus, Chaetornis, Gramnicola, Schoenicola), and other allied genera, which comprise the subfamily Megalurinae in the Sibley and Ahlquist system; (5) the remaining genera of the traditional Sylviidae, most of which appear to fall within a clade represented by Sibley and Ahlquist's Acrocephalinae subfamily. Groups three, four and five above, plus the Garrulax laughing thrushes comprise Sibley and Ahlquist's more restricted Sylviidae, hereafter referred to as Sylviidae sensu strictu.
Little is known about the evolutionary history of passerines. The prevailing opinion has been that passerines arose in the Tertiary, specifically in the early Eocene, then underwent a dramatic diversification during the Miocene. The oldest putative passerine fossils are from early Eocene Australia (ca. 54 million years ago), lending support to a Southern Hemisphere origin, since passerine fossils do not appear in the Northern Hemisphere until the Oligocene. By the lower Miocene, passerine fossils greatly outnumber all other taxa in many Northern Hemisphere sites. A recent molecular study suggests that the passerine divergence may be much older and that passerines evolved on Gondwana, the Cretaceous supercontinent in the southern hemisphere. If this is the case, oscine passerines may have diverged from suboscine passerines when Australia separated from Gondwana, radiated on Australia, then dispersed throughout the Old World when Australia came in contact with Southeast Asia.
Within the Sylviidae sensu strictu, the first divergence was probably between Sibley & Ahlquist's Acrocephaline sub-family (Acrocephalus, Hippolais, Phylloscopus, Seicercus, Sylvietta, Sphenoeacus, etc.) and the lineage leading to the other three subfamilies. Next to diverge was Garrulax, the laughingthrushes, which diverged from a lineage leading to the Timaliine babbers and Sylvia and Parisoma warblers. The genus Sylvia is thought to be at least 12-16 million years old. The Phylloscopus radiation is about as old as Sylvia, while the Acrocephalus/Hippolais radiation is only about half as old. These estimates place much of the sylviid radiation during the Miocene and Pliocene epochs of the mid-Tertiary, consistent with the passerine radiation in the fossil record.
Physical characteristics
The traits that have been used to characterize Sylviidae sensu latu are: unspotted young (as opposed to the Old World flycatchers and thrushes); rictal bristles at the base of the bill (a widespread adaptation for insectivory); thin, pointed bill; hatchlings naked or only partially downy; ten primaries; scutellate tarsi; and lack of strong sexual dimorphism (Sylvia is a notable exception). Most genera have twelve tail feathers, but there are a few exceptions. Wing shape and length ranges from short and rounded in sedentary species, to longer and more pointed in long-distance migrants. Moult timing and pattern are highly variable.
Sylviids are typically dull in color; often in shades of brown, green, yellow, and gray. The family includes some of the tiniest songbirds in the world, the kinglets, as well as some small wren-like birds, many small warblers, and the medium-sized marsh warblers and grassbirds. The smallest sylviids, the kinglets, weigh only a few grams. The largest, the marsh warblers Acrocephalus and the grassbirds Megalurus can weigh close to 2 oz (60 g). A comprehensive summary of longevity data is unavailable, but many species live at least 8–12 years.
While most species do not have distinctive breeding plumages like those of the New World warblers (Parulidae), a few sylviids show a marked contrast between breeding and nonbreeding plumages. A striking example is the red-winged warbler (Heliolais erythroptera), the only member of a genus apparently closely related to Prinia. While breeding red-winged warblers of both sexes have dark gray upperparts and tail, they become predominantly tawny-brown in nonbreeding plumage. A somewhat less striking example is the genus Cisticola. Members of this genus undergo two moults each season, and most have shorter tails and slightly different plumage coloration during the breeding season. A few members of the genus Prinia have similar distinct seasonal plumage variation.
Distribution
The Old World warblers are extraordinarily widespread, occuring on every continent except South America and Antarctica. If the Polioptilinae are included, there are representatives of Sylviidae sensu latu in South America as well. Most of the sylviid diversity occurs in the African and Oriental faunal regions, with a less diverse, but widespread group of species in the Palearctic. Nearctic and Australian species represent recent invasions from Siberia and Southeast Asia, respectively.
The centers of distribution for some major sylviid genera are as follows. Sino-Himalayan Region: Bradypterus, Cettia, Phylloscopus, Seicercus, Prinia; Southeast Asia: Megalurus and allies, Orthotomus; Temperate Asia (Palearctic): Locustella, Acrocephalus, Hippolais; Africa: Cisticola and allies; Mediterranean/Middle Eastern (Palearctic) region: Sylvia. Relatively little exchange has occurred between Northern (Palearctic) and Southern (Oriental and African) Hemisphere faunas in the Old World, perhaps due to the East/West orientation of major barriers, including the Sahara and Gobi deserts, the Himalayas, the Alps, the Atlas, Caucasus, and other mountain ranges, and historically, the Tethys sea, which separated Africa from what is now the Palearctic. Conversely, in the Americas, where the major barriers are oriented North to South, many Neotropical migrant families originated in South America, then spread north to the Nearctic. Voous (1977) is of the opinion that all Old World sylviids arose in either the Indo-African region or the Sino-Himalayan region. While these are areas where the largest radiations have taken place, it is not clear where the common ancestor of the modern Sylviidae arose.
Habitat
The Old World warblers occupy an astonishing variety of habitats, from montane and riparian forests to arid scrublands to marshes and river floodplains to city parks and backyards. Sylviids are found in all extremes of water availability with the exception of open water and harsh deserts. The family is represented at a wide range of altitudes, from lowlands at or near sea level to montane forests and dwarf scrub as high as several thousand meters. Considerable habitat adaptability is demonstrated by the varied habitats occupied by Acrocephalus warblers that have colonized oceanic islands.
Habitat partitioning is widespread among sylviid warblers. An example of foraging height segregation is found in the Sylvietta crombecs. The long-billed crombec is restricted to undergrowth in areas of sympatry with red-faced and redcapped crombecs. In other areas, the long-billed crombec is found at higher levels in the forest, demonstrating that competition limits the ability of this species to fully exploit its potential niche. Habitat partitioning also occurs in syntopic species of Sylvia, but there is considerable overlap, leading to interspecific territorial interactions.
Exploitation of topological niches within a habitat has been suggested as an important step in ecological and morphological divergence of closely related species. Adam Richman and Trevor Price have shown, in a 1992 study, that such a scenario has apparently occurred among a group of sympatric Phylloscopus warblers in the Himalayas. A related phenomenon is replacement, the presence of closely related species in different habitat types, with little overlap. Replacement is essentially habitat partitioning on a larger scale. Many Afrotropical genera contain closely-related species that occupy similar ecological niches in dissimilar habitats.
Behavior
Sylviids range from highly arboreal to almost entirely terrestrial. They are generally very active but often quite secretive and skulking. Most species inhabit dense vegetation, and are most easily located and identified by voice. The carriage of many of the Old World warblers is more or less horizontal. Flight ranges from very weak in some sedentary Afrotropical species, to strong and sustained in long-distance migrants. The gait is typically a hop, but some species run.
Resources
Books:Ali, Salim, and S. Dillon Ripley. Handbook of the Birds of India and Pakistan, 2nd ed. Vol. 8. Warblers to Redstarts. Delhi: Oxford University Press, 1997.
Baker, Kevin. Warblers of Europe, Asia and North Africa. Princeton: Princeton University Press, 1997.
Cramp, Stanley, ed. The Birds of the Western Palearctic. Vol. 6. Warblers. Oxford: Oxford University Press, 1992.
Kaufman, Kenn. Lives of North American Birds. New York: Houghton Mifflin, 1996.
Parmenter, Tim and Clive Byers. A Guide to the Warblers of the Western Palearctic. Uxbridge, Middlesex: Bruce Coleman Books, 1991.
Shirihai, Hadoram, Gabriel Gargallo, and Andreas J. Helbig. Sylvia Warblers. Princeton: Princeton University Press, 2001.
Sibley, Charles G. and Jon E. Ahlquist. Phylogeny and Classification of Birds. New Haven, Yale University Press, 1990.
Urban, Emil K., Hilary C. Fry, and Stuart Keith. The Birds of Africa. Vol. 5. San Diego: Academic Press, 1997.
Periodicals:Alström, P. and U. Olsson. "The golden-spectacled warbler: a complex of sibling species, including a previously undescribed species." Ibis 151 (1999): 545–568.
Barker, F. Keith, et al. "A phylogenetic hypothesis for passerine birds: taxonomic and biogeographic implications of an analysis of nuclear DNA sequence data." Proceedings of the Royal Society of London, Series B, 269 (2002): 295–308.
Catchpole, Clive K. "The evolution of mating systems in Acrocephalus warblers." Japanese Journal of Ornithology 44 (1995): 195–207.
Helbig, Andreas J. and Ingrid Seibold. "Molecular phylogeny of Palearctic-African Acrocephalus and Hippolais warblers (Aves: Sylviidae)." Molecular Phylogenetics and Evolution 11 (1999): 246–260.
Irwin, Darren E., et al. "Speciation in a ring." Nature 409 (2001): 333–337.
Leisler, B., et al. "Taxonomy and phylogeny of reed warblers (genus Acrocephalus) based on mtDNA sequences and morphology." Journal fur Ornithologie 138 (1997): 469–496.
[Article by: Matthew J. Sarver, BS]
