Dartford Warbler Curruca undata Scientific name definitions

12·5 cm; 6·8–10·5 g. Small and graceful warbler with very long tail, short rounded wings. Male nominate race breeding has slaty ash-grey head and upperparts ; remiges and upperwing-coverts blackish-grey with pale grey fringes; alula blackish, fringed whitish, narrowly so on largest feather; tail black, outermost rectrix with white tip and outer edge, adjacent feather with slightly less white, next two with at most whitish-grey tips; vinous reddish-brown below , distinct whitish speckling on throat, contrastingly whitish mid-belly, greyish tinge on rear flanks and vent; iris deep orange-brown, orbital ring reddish  , eyering with pinkish, whitish and grey feathers; bill blackish, pale greyish-pink cutting edges of upper mandible and base of lower mandible; legs mostly orange-brown. Male in non-breeding plumage is distinctly tinged brownish above and whitish below. Female breeding resembles breeding male, but has browner upperparts, paler and pinker underparts; non-breeding female similar but still browner above, and with fresh whitish feather tips concealing pinkish orange-brown underparts. Juvenile is dark grey-brown above and pale buffish-brown below , tail dark grey-brown with pale tips and edges of outer feathers reduced and more creamy-buff, iris mostly greyish olive-brown, orbital ring pale orange-red, eyering whitish to buffish; first-winter like respective adult, but with juvenile-like bare parts and unmoulted flight-feathers. Races differ primarily in colour tones: male toni is slightly duller above and (especially when plumage fresh) with sandier tinge than in nominate, more saturated below; male <em>dartfordiensis</em> has upperparts markedly suffused dark earth-brown (particularly when fresh), more deeply coloured dark wine-brown  below.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Favours dense and homogeneous scrub  , garrigue and low maquis c. 0·5–1·5 m tall and dominated by such species as gorse (Ulex), heaths (Erica), rosemary (Rosmarinus), Genista, Cistus and kermes oak (Quercus coccifera); in N of range mostly lowlands with Erica/Calluna heathland and gorse. Occurs also in areas of dense bramble (Rubus fruticosus), and colonizes the scrubby formations typical of first stages of wildfire succession. Avoids forested areas, but can be found in open woodland with dense scrubby undergrowth and young, bushy pine (Pinus) plantations. In non-breeding season, also occupies Salicornia scrub, sparser scrub and garrigue, and grassy steppes. Lowlands (down to sea-level), and to c. 1200 m in Corsica and 1800–2000 m in Pyrenees, C Spain and NW Africa.

Adults largely resident in most of range; vacate breeding territories only under very extreme winter weather conditions  , even at high elevations (e.g. Pyrenees) and in N of range (S England). Most movements over short distance and dispersive in nature, involving mainly first-year individuals; some individuals of European origin migrate to non-breeding grounds in NW Africa, and race dartfordiensis known to reach Balearic Is (thus not avoiding sea crossing); nocturnal restlessness of hand-reared young higher than that of young C. melanocephala and C. balearica. Autumn movements especially noticeable from mid-Sept to Nov; non-breeding areas occupied mostly from Nov to Mar, vacated from Feb onwards, spring migration mostly in Mar. In England, juvenile dispersal usually reaches 1–6 km. Moves singly or in pairs; first-years sometimes form loose groups of up to 10–15 individuals between late summer and winter.

Mostly arthropods ; also berries outside breeding season. Invertebrate food includes adult and larval moths and butterflies (Lepidoptera), damselflies (Odonata), grasshoppers (Orthoptera), bugs (Hemiptera), harvestmen (Opiliones), millipedes (Diplopoda), snails (Mollusca) and, particularly in winter, spiders (Araneae) and beetles (Coleoptera). Some arthropods seemingly avoided, e.g. ants (Formicidae), ladybirds (Coccinellidae), woodlice (Isopoda), pine-sawfly larvae (Diprionidae) and various hemipterans (particularly Orthotylus). In detailed year-round study in S England, diet comprised 36% beetles, 18% caterpillars, 17% spiders and harvestmen, 17% hemipterans, 8% flies (Diptera) and 4% others. Nestlings fed solely with arthropods, mostly caterpillars, beetles and spiders; in S England nestling diet varies according to precise habitat characteristics, mainly caterpillars (43%) and spiders (42%) in territories in gorse-rich areas, but caterpillars only 26% and spiders 29% in areas without gorse. Fruits taken in late summer and winter, include those of genera Rubus, Daphne, Myrtus, Rhamnus, Myoporum, Pistacia, Vaccinium, Phyllirea and Phytolacca. Forages low in vegetation, usually c. 0·5–2 m above ground, mostly in scrub and bushes, not infrequently also higher up in tall bushes and trees (e.g. pines); in S England marked preference for foraging in gorse (much richer in invertebrates), rather than in heather, particularly during breeding season (when 87% of foraging time spent in gorse). On rare occasions, feeds directly on ground, or seizes flying insects while in flight. In parts of its range associates with Common Stonechat (Saxicola torquatus), especially outside breeding season, using that species as a sentinel. Usually solitary or in pairs, occasionally in small groups; in England, known to form communal winter roosts of at least c. 6–8 individuals.

Song , from cover or bushtop or in song flight, a rather short and hurried warble (c. 1–3·5 seconds long), distinctly grating and metallic, characteristically involving piping and call-like notes and, especially in S of range, rattling “tr”-like sounds; longer and richer in song flight. Call a grating “tchairr”, in hurried, nervous series when alarmed.

Season mostly mid-Mar to Aug; laying from mid-Mar to late Mar in Iberian Peninsula, Balearic Is (Menorca) and Channel Is, early Apr in S France and NW Africa (Algeria), and usually by mid-Apr in S England; mostly two broods, in England sometimes up to three (rarely, four), but apparently single-brooded in Sardinia and parts of S France. Monogamous, with instances of a second male helping at nest. Territorial. Song-flighting male rises rapidly to 6–7 m above ground, hovering and fluttering up and down, then parachutes down to cover or perch. Male builds flimsy “cock nests”, one of which sometimes completed by female for breeding, but generally breeding nest constructed by both sexes, a deep cup of grass, vegetable down and cobwebs, lined with finer rootlets and hair, placed c. 0·25–0·5 m above ground in low dense vegetation in scrub or bush (e.g. Rosmarinus, Erica, Ulex, Calluna). Clutch 3–6 eggs, usually 4–5 (average 4 in S England), clutch size increasing from early May to mid-Jun and then declining; incubation by both parents, female taking largest share (two-thirds of daytime and throughout night), usually from penultimate egg, period 12–14 days; chicks fed by both parents, nestling period c. 12 days; fledglings dependent on parents for further 10–15 days. Reported breeding success 67% in France (Fontainebleau), 56% in S England (hatching 63%, fledging 89%). Average annual survival of adults at least 50% in England; in mild winters adult mortality below 39% in Fontainebleau (France).

Not globally threatened. Currently considered Near Threatened. Rather patchily distributed throughout its range, but locally common to very common. Population in Europe (95% of species’ breeding range) estimated to total 1,900,000–3,700,000 breeding pairs by year 2000. Breeding densities usually c. 2–10 pairs/10 ha in suitable areas, but up to 15–25 pairs/10 ha in optimal habitat, e.g. 16–17 pairs/10 ha in burnt cork oak (Quercus suber) forest; reaches 5 pairs/10 ha at 2000 m in mountain shrublands of E Pyrenees; in S England, 3·5–5 pairs/10 ha in best habitats but decreases to 1–2 pairs/10 ha in less suitable and more fragmented areas. In Balearic Is, has bred on Menorca since at least 1970s, probably earlier (but situation confused by misidentification of present species as C. balearica); in 1997 colonized N Mallorca, where total population estimated at c. 50–100 breeding pairs in 2005. Considered to have decreased in mainland Spain between 1970 and 1990, but stable in rest of European range . Sensitive to fragmentation and loss of suitable habitat caused by agricultural intensification, urban development and afforestation; in S England, natural succession of heathland and also habitat fragmentation are main threats. Wildfires can be temporarily and locally detrimental, but help to create new habitat and prevent succession of scrub and maquis to forest, thus favouring the species in long term; in Mediterranean region can colonize burnt areas in second year after fire and breed there for at least a decade; optimal conditions in S England burnt areas, however, reached only 10 years after. Sensitive to very harsh winters, particularly in far N of range; S England population reduced to critically low numbers after severe winters, e.g. just 11 pairs after extreme winter of 1962/63, but recovered after series of mild winters (c. 2500 pairs in 2002; c. 3100 territories in 2006 (1 Wotton, S., Conway, G., Eaton, M., Henderson, I. and Grice, P. (2009). The status of the Dartford Warbler in the UK and the Channel Islands in 2006. British Birds. 102(5): 230–246. Close ) ).