The garden warbler (Sylvia borin) is a common and widespread small bird that breeds in most of Europe and in the Palearctic to western Siberia.

It is a plain, long-winged and long-tailed typical warbler with brown upperparts and dull white underparts; the sexes are similar and juveniles resemble the adults.

The garden warbler's rich melodic song is similar to that of the blackcap, its closest relative, which competes with it for territory when nesting in the same woodland.

The preferred breeding habitat in Eurasia is open woodland with dense low cover for nesting; despite its name, gardens are rarely occupied by this small passerine bird.

The clutch of four or five blotched cream or white eggs is laid in a robust cup-shaped nest built near the ground and concealed by dense vegetation.

Insects are the main food in the breeding season, although fruit predominates when birds are fattening prior to migration, figs being a particular favourite where available.

The garden warbler is hunted by Eurasian sparrowhawks and domestic cats, and its eggs and nestlings are taken by a variety of mammalian and avian predators.

The large and fairly stable numbers and huge range of the garden warbler mean that it is classed as least concern by the International Union for Conservation of Nature.

[2] The garden warbler and its nearest relative, the blackcap, are an ancient species pair which diverged very early from the rest of the genus, between 12 and 16 million years ago.

In the course of time, these two species have become sufficiently distinctive that they have been placed in separate subgenera, with the blackcap in subgenus Sylvia and the garden warbler in Epilais.

[4] The nearest relatives of the garden warbler outside the sister group are believed to be the African hill babbler and Dohrn's thrush-babbler.

[15] Intermediate birds occur where the recognised forms meet and interbreed, and have sometimes been given subspecies status, including S. b. kreczmeri in Poland and S. b. pateffi in Bulgaria, but these are not generally accepted as valid taxa.

The eastern subspecies S. b. woodwardi is slightly larger and paler than the nominate form with a greyer tone to the upperparts and whiter underparts.

[15] The subspecies are hard to distinguish visually where they occur together in Africa, but a wing length greater than 80 mm (3.1 in) confirms S. b. woodwardi when birds are trapped.

[15] Juvenile garden warblers have a partial moult mainly involving the body plumage between June and September prior to migration.

[18] Subsong may be heard on the wintering grounds in Africa, developing into the full song in March and April prior to the return to Europe.

[22] This warbler has occurred as a vagrant in Afghanistan, Djibouti, Iceland, São Tomé and Príncipe, Somalia, Yemen, Svalbard, Jan Mayen and Madeira.

[17][24] The breeding habitat of the garden warbler is open areas with dense bushes, including thickets and woodland edges.

Shady areas and a bushy or herbaceous undergrowth are preferred, as are woods adjacent to rivers or reed beds; in Ireland it favours thickets on the shores of small lakes.

A tolerance of willow, alder and birch allows it to breed farther north and at higher altitudes than any other European Sylvia warbler.

[25][26] Similar songs are a feature of the Sylvia warblers as a group, and it has been suggested that this promotes interspecific competition and helps to segregate territories between related species.

[27][28] However, it appears more likely from later studies that segregation of sympatric species, other than the blackcap and garden warbler, is due to subtle differences in habitat preferences rather than interspecies aggression.

[22] The short incubation and fledging times may be a result of predation pressure, the rapid development of the chicks enabling them to leave the vulnerable nest as early as possible, even while still flightless.

[19] On this diet a bird can gain weight quickly and the liver increases the rate at which it produces fatty acids for storage in adipose tissue.

[39] Most internal organs (including the liver, spleen, intestines, kidneys and heart) and the flight muscles lose weight during the journey over the Sahara, although the testes quadruple in mass in preparation for the breeding season.

[48] External parasites of the garden warbler include the fleas Ceratophyllus gallinae and Dasypsyllus gallinulae and the mite Syringophilosis borini, named after its host.

Seventeen further members of that group are found only in the blackcap, and another three occur in the African hill babbler, supporting the shared ancestry of the three bird species.

[5] The garden warbler has a very large range of 9,650,000 km2 (3,730,000 sq mi), and its population in Europe is estimated at 17–31 million breeding pairs.

[53] The composer Olivier Messiaen used the song of the garden warbler as the basis for his 1971 solo piano piece La fauvette des jardins, the title being the French name of the species.

French epicure Jean Anthelme Brillat-Savarin said of the warbler when cooked like ortolan bunting "if it were the size of a pheasant, it would be worth an acre of land".