Wood Warbler Phylloscopus sibilatrix Scientific name definitions

11–13 cm; 6·4–15 g. A medium-sized to large leaf-warbler with long pointed wings and relatively short tail, bright green upperparts, well-defined supercilium, and yellow breast contrasting with white of lower body. Has long pale yellow supercilium tapering over ear-coverts, and equally long but narrow dark olive-green eyestripe; above, almost entirely bright green (slightly greyer when in worn plumage), fringes of median and greater upperwing-coverts and edges of flight-feathers yellow­ish-green and contrasting with dark brown of inner webs (pale edges can at times form panel on closed wing), fringes of tertials yellowish-white; outer tail feathers edged yellowish-green; cheek, ear-coverts, chin and throat  to upper breast bright yellow, rest of underparts pure white ; exceptional individuals lack bright yellow on face and throat, or have brown upperparts; iris dark brown; upper mandible brown or light brown, lower mandible mostly yellowish-pink; legs  brown to yellowish-brown. Distinguished from P. trochilus, P. bonelli and P. orientalis by combination of bright green upperparts, bright yellow supercilium and face to upper breast and pure white rest of underparts, also somewhat larger in size, with longer wings and shorter tail; from smaller P. nitidus by lack of wingbars, bare-part colours, subtle differences in tone of green on upperparts. Sexes alike. Juvenile is duller than adult, with greyer tinge on upperparts, generally less extensive yellow on throat and breast.

Occasional hybridization recorded with P. bonelli. Original description traditionally attributed to reference by same author in following year; original spelling in currently used reference is a Latin word incorrectly spelt, which must therefore be corrected. Monotypic.

• Wood x Western Bonelli's Warbler (hybrid) Phylloscopus sibilatrix x bonelli

W Norway, British Is and W & S France E to SC Siberia and S through Italy, extreme N Greece, NW Turkey (1 Özkan, K. (2011). An avifaunal survey of the Istranca mountains, Turkish Thrace: novel breeding bird records including the first breeding record of Wood Warbler Phylloscopus sibilatrix in Turkey. Sandgrouse 33(2): 163–173. Close ) and SW & C Ukraine; also disjunctly in Crimea and NW Caucasus and, rarely, in NE Kazakhstan (2 Gavrilov, E. I., and A. E. Gavrilov (2005). The Birds of Kazakhstan. Abridged edition. Tethys Ornithological Research 2. Tethys, Almaty, Kazakhstan. Close ). Winters in Africa mainly from Sierra Leone and S Guinea E to S South Sudan, N DRCongo, Uganda, Rwanda, Kenya and S Somalia.

Breeds in moist and shady lowland deciduous woods, typically beech (Fagus), mixed oak (Quercus), hornbeam (Carpinus) and sweet chestnut (Castanea), with closed canopy and sparse undergrowth; also in mixed stands of spruce (Picea), alder (Alnus), birch (Betula), pine (Pinus) or occasionally ash (Fraxinus). Mixed stands with trees of mixed ages spaced well apart form optimum breeding woods. In African non-breeding quarters inhabits humid evergreen forest, moist thickets, forest edge, dry woodland and forested mountain slopes, as well as wooded savanna and scattered trees in forest clearings; often in fig trees (Ficus), occasionally in mangroves. On passage occurs also in low trees and bushes.

Migratory. Spends non-breeding season in guinean forest of sub-Saharan Africa. European population crosses Mediterranean mainly between Italy and Aegean Sea (only small numbers crossing at W end) from mid-Jul, but main departure in Aug. Most have left NW Europe by mid-Sept, slightly later in E Europe, possibly reflecting later departure from Russian breeding area, with main passage from W Russia mid-Sept to mid-Oct; passage through Greece, Albania and NW Turkey throughout Oct, and to end of the month in Malta; only small numbers recorded in Egypt and NW Libya, suggesting that many move from S Europe to S of Sahara in single flight. Arrives Nigeria and Cameroon late Aug, Burkina Faso in early Sept, Ivory Coast E to N DRCongo and Gabon in Oct; reaches Sierra Leone in Nov and small numbers in Liberia in Dec. In E passage continues in SW Russia and Iran in Oct, uncommon on passage through United Arab Emirates Sept and early Oct, arrival Ethiopia (where scarce) in Nov and frequently abundant on passage in W Sudan; wintering population in S Somalia present mid-Oct to early Apr. Return passage begins Mar, but main departure Apr to mid-May; passage notably W of route taken in autumn, many departing W Africa from late Mar, continuing to early May in N Ghana; rare Burkina Faso, Mali and Senegal and absent throughout most of Sahara, including Mauritania; common and widespread in Apr from Morocco E to N Tunisia and N Libya, so presumably makes crossing in single flight; variable yearly passage through parts of N Egypt and throughout Arabia early Apr to early May. Passage in S Europe chiefly from mid-Apr and arrival in W & C European breeding areas second half Apr, first arrivals in Finland and European Russia early May; males arrive and establish territory up to one week before females. Vagrants recorded C Siberia, Japan, Seychelles, Aldabra, Amirantes, Madeira, Iceland, Faeroes, Portugal and Kuwait.

Food principally invertebrates  ; some fruit also taken. Most items are adult mayflies (Ephemeroptera), damselflies (Odonata), stoneflies (Plecoptera), earwigs (Dermaptera), bugs (Hemiptera), lacewings (Neuroptera), scorpion flies (Mecoptera), larval and adult moths (Lepidoptera), caddis flies (Trichoptera), flies (Diptera), sawflies (Symphyta), ants (Formicidae), larval and adult beetles (Coleoptera), spiders (Araneae), harvestmen (Opiliones) and small molluscs. Fruits include bramble (Rubus fruticosus), elder (Sambucus), currant (Ribes), bilberry (Vaccinium), plum (Prunus) and alder-buckthorn (Frangula). Nestlings fed principally with caterpillars and other larvae, with increasing amounts of adult flies. Usually forages alone or in pairs, but recorded in winter in groups of 3–4 and may join mixed-species feeding flocks; sometimes larger flocks, of up to 15 or more, on passage. Forages mostly in canopy and undergrowth, by actively and purposefully inspecting leaves and branches of trees and bushes; also hovers, and makes frequent sallies after passing insects.

Song , mostly mid-Apr to early Jul but regularly from Feb on migration, also irregularly in wintering area, a series of rising and accelerating “sip” notes followed by short but fast, sibilant and descending shimmering trill , “sip sip sip sirrrrrrrrrrrrrrrrrrrrrrrr”, lasting for c. 3 seconds (shivers wings and tail during singing); very similar to songs of P. bonelli and P. orientalis but faster, with accelerating rising start, and the trill then running down as flourishing conclusion. Also a variable series of soft, clear, piping “pew” or “tiu” notes, which may be given separately or in between trills. Call a single-note “pew” uttered with variable emphasis, and similar to notes in piping song; also “tee” and “tiu” together with sharp “pit” or “sip” notes, used in aggression. Nestlings give “ztztzt” food call, and sharper or high-pitched “dschi” and “tschie-tschie-tschie” while being fed.

May–Jul; usually single-brooded, in C France sometimes two broods. Mostly monogamous, also frequently polygamous. Territory established by male and defended by both sexes, but tolerant of other territory-owners within established territory; territory may overlap with that of P. trochilus. Male performs song flight over any female entering territory, female responds with soft contact note, male approaches in slow butterly-like flight and chases her; when perched close to female, male holds crown and nape feathers raised and makes bowing movements, puffs out breast and shivers wings, with primaries held beside body at same time as tail is fanned; occasionally swivels body to left and right; female may respond by wing-shivering, although this less vigorous than male’s. Nest-site selected by female, which also builds nest, usually within 3–4 days, from material collected from within c. 10 m of site; nest a ball of dry grasses , leaves, plant stems and fibres, bark strips and animal hair, built on ground, occasionally under fallen tree or roots; territory up to 3·6 ha, but average size smaller, 0·05 ha, especially in areas of high density, and territories of polygamous males on average slightly larger than those of monogamous males. Clutch 5–7 eggs , exceptional limits 2–10; incubation by female, period 12–14 days; chicks cared for by both parents, fledge after 11–13 days; young fed by parents for 2–3 days after leaving nest, but family-members remain together for up to 4 weeks. Breeding success fairly high; at one study site in Belgium, of 84 eggs laid in 14 nests in one year 66 young fledged (79% success), and in second year fledging success between 31% and 58%; in another study in Switzerland, 46·9% nest survival over an average nesting period of 31 days, nest predation accounting for 79% of all nest losses (3 Grendelmeier, A., Arlettaz, R., Gerber, M. and Pasinelli, G. (2015). Reproductive performance of a declining forest passerine in relation to environmental and social factors: implications for species conservation. PLOS One. 10(7): e0130954. Close ). Breeds in first year. Longevity generally 1–4 years, but oldest known ringed individual 6 years 1 month.

Not globally threatened. Locally common. Population in Europe stable and estimated at between 6,000,000 and 7,000,000 pairs, with most in Germany, Estonia and Latvia. Belarus population estimated at approximately 25 million pairs, an indication that population in Russia may be towards upper end of estimated range of 10,000,000–100,000,000 pairs. Some evidence of expansion in N of range, in Norway and Finland, but generally considered to be limited by early summer temperatures, coincides with climatic amelioration since early 1960s. In Britain, at NW end of range, population, based on surveys in mid-1980s, was estimated to be 17,200 males, and little evidence that this figure has changed greatly since then; since 1980s has bred annually, and in increasing numbers, in Ireland.