Dartford warbler

The Dartford warbler (Curruca undata) is a typical warbler from the warmer parts of western Europe and northwestern Africa. It is a small warbler with a long thin tail and a thin pointed bill. The adult male has grey-brown upperparts and is dull reddish-brown below except for the centre of the belly which has a dirty white patch. It has light speckles on the throat and a red eye-ring. The sexes are similar but the adult female is usually less grey above and paler below.

Dartford warbler
Female in Spain
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Sylviidae
Genus: Curruca
Species:
C. undata
Binomial name
Curruca undata
(Boddaert, 1783)

Its breeding range lies west of a line from southern England to the heel of Italy (southern Apulia). The Dartford warbler is usually resident all year in its breeding range, but there is some limited migration.

Taxonomy and systematics

The Dartford warbler was first described by the Welsh naturalist Thomas Pennant. He based his description on two specimens that obtained by the ornithologist, John Latham in April 1773 on Bexley Heath, near Dartford in Kent.[2][3][4] Pennant asked Latham to name the new and till then unnamed bird, and Latham chose Sylvia dartfordiensis, or Dartford Warbler.[5] The species was assigned the binomial name of Motacilla undata by the Dutch naturalist Pieter Boddaert in 1783 based on a coloured plate in Edmé-Louis Daubenton's Planches enluminées d'histoire naturelle.[6][7]

John Latham, in 1816

The specific undata is from Medieval Latin undatus, "with wavy markings".[8]

The type locality of the Dartford warbler is Provence in France. This species probably forms a superspecies with Tristram's warbler and this in turn seems close to Marmora's warbler and the Balearic warbler.[9][10] Altogether, this group of typical warblers bears a resemblance to the wrentit, the only species of Sylviidae from the Americas. However the wrentit is less closely related to the genus Sylvia than to the parrotbills.[11][12] Its visual similarity to the Dartford warbler group is an example of convergent evolution.

Three subspecies are recognised:[13][14]

  • C. u. dartfordiensis Latham, 1787 – south England and north-west France[15][16]
  • C. u. toni Hartert, 1909 – north-west Africa[15][17]
  • C. u. undata (Boddaert, 1783) – Iberian Peninsula and south France[6][15]
Male Dartford warbler

Description

The Dartford warbler is a small (13 cm (5.1 in)) passerine bird, distinguished by its long tail compared with that of other warblers. Its plumage comprises unobtrusive and muted tones, which blend in with the dry dead plants, old wood or sunny greyish wood found in its preferred habitats.

Like many typical warblers, the Dartford warbler has distinct male and female plumages. The male has a grey back and head, reddish underparts, and a red eye. The reddish throat is spotted with white. The sides are a dull greyish tone, being more clear about the abdomen. In some populations males have bluish-grey or brownish-grey backs and heads. The female is paler below, especially on the throat, and a browner grey above. The female's throat also has white spots, although they are smaller and less marked than in the male. Juvenile birds are similar to females.

Distribution and habitat

The species is naturally rare. The largest European populations of Curruca undata are in the Iberian peninsula, others in much of France, in Italy and southern England and south Wales. In Africa it can be found only in small areas in the north, wintering in northern Morocco and northern Algeria.

Behaviour and ecology
Eggs at the Muséum de Toulouse

Breeding

Dartford warblers first breed when they are one year old. They are usually monogamous and the pair bond can persist from one year to the next. The male sometimes builds several simple nests (cock nests) of which one is chosen by the female,[18] but it is more usual for both birds to participate in constructing the breeding nest.[14] In southern England the birds breed on heathlands, sometimes near the coast, and nest in either common gorse (Ulex europaeus) or common heather (Calluna vulgaris).[19] The compact cup-shaped nest is located in dense bushes, usually within 60 cm (24 in) of the ground.[19] It is formed mainly of grasses and is lined with a layer of finer material that can include thin roots and feathers.[20][21] The eggs are laid from early April in southern France and Spain, and from mid-April in southern England.[20] The clutch is typically 3–5 eggs which are smooth and glossy, with a white or occasionally pale green ground and marked with brown speckles which are sometimes concentrated at the larger end.[20][21] The average size of an egg is 17 mm × 13 mm (0.67 in × 0.51 in) with a weight of 1.4 g (0.049 oz) of which 6 percent is shell.[22] The eggs are incubated for 12–14 days mainly by the female.[23] The chicks are fed arthropods by both parents. The nestlings fledge 10–14 days after hatching and are then fed by their parents for a further two weeks.[23] Usually two and occasionally three broods are raised in a year.[20]

Feeding

It inhabits open fields with degraded scrub brush and is common in heather. In winter it may visit urban areas, but always feeds within shrubs in these areas. Nests in bushes with thorns and near the ground. These warblers are mostly insectivorous, eating caterpillars, butterflies, beetles and spiders.

The song of the Dartford warbler is a distinctive rattling warble.

Status and conservation

Dartford warblers almost died out in the United Kingdom in the severe winter of 1962/1963 when the national population dropped to just ten pairs. Sylvia undata is also sensitive to drought affecting breeding success or producing heath fires, as occurred during 1975 and 1976 in England when virtually all juveniles failed to survive their first year.[24]

However, this species can recover well in good quality habitat with favourable temperatures and rainfall, thanks to repeated nesting and a high survival rate for the young. Indeed, they recovered in some areas of the UK, but numbers are once again on the decline in other regions of their natural range.

The range of the Dartford warbler is restricted to western and southern Europe. The total population in 2012 was estimated at 1.1–2.5 million breeding pairs. The largest numbers occur in Spain where there were believed to be 983,000–1,750,000 pairs. For reasons that probably include loss of suitable habitat, the Spanish population appears to be declining. The species is therefore classed by the International Union for Conservation of Nature as being Near threatened.[25]

A period of climatic warming since 1963 has seen the UK population increase to "more than 2,500 pairs in 2006 (Wotton et al. 2009). Expansion into patches of structurally suitable habitat (up to an altitude of 400m), more northerly areas and away from the core of the range, from Dorset and Hampshire to Derbyshire and Suffolk, is likely to have been facilitated by milder winter weather (Wotton et al. 2009, Bradbury et al. 2011)... The Dartford warbler population in the UK is expected to continue to increase. However, future climate-based projections for the European range indicate that by 2080, more than 60% of the current European range may no longer be suitable (Huntley et al 2007). There is evidence that this is happening already, with severe declines in Spain and France (Green 2017). For this reason, the species is classified as Near Threatened on the IUCN Global Red List. If the declines in southern Europe continue, the UK will become increasingly important for global conservation of this species".[26]

References
  1. BirdLife International (2012). "Sylvia undata". IUCN Red List of Threatened Species. 2012. Retrieved 26 November 2013.
  2. Bibby, C.F.; Tubbs, C.R. (1975). "Status, habitats and conservation of the Dartford Warbler in England" (PDF). British Birds. 68 (5): 177–195.
  3. Pennant, Thomas (1776). British Zoology, Volume 1 (4th ed.). Warrington, United Kingdom: Printed by William Eyres, for Benjamin White. p. 389.
  4. Latham, John (1783). A General Synopsis of Birds, Volume 2. London: Printed for Benj. White. p. 435.
  5. Moss, Stephen (2018). "4 (1)". Mrs Moreau's Warbler: How Birds Got Their Names. Google Books: Faber & Faber. ISBN 9781783350926. Retrieved 24 December 2019.
  6. Boddaert, Pieter (1783). Table des planches enluminéez d'histoire naturelle de M. D'Aubenton : avec les denominations de M.M. de Buffon, Brisson, Edwards, Linnaeus et Latham, precedé d'une notice des principaux ouvrages zoologiques enluminés (in French). Utrecht. p. 40 Number 655.
  7. Daubenton, Edme-Louis (1765–1783). Planches enluminées d'histoire naturelle, Volume 7. Plate 655, Le Pitte-chou de provence.
  8. Jobling, James A (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. pp. 376, 395. ISBN 978-1-4081-2501-4.
  9. Shirihai, Gargallo & Helbig 2001, pp. 24–29.
  10. Jønsson, Knud A.; Fjeldså, Jon (2006). "A phylogenetic supertree of oscine passerine birds (Aves: Passeri)". Zoologica Scripta. 35 (2): 149–186. doi:10.1111/j.1463-6409.2006.00221.x.
  11. Cibois, Alice (2003). "Mitochondrial DNA phylogeny of babblers (Timaliidae)". The Auk. 120 (1): 35–54. doi:10.1642/0004-8038(2003)120[0035:MDPOBT]2.0.CO;2. JSTOR 4090138.
  12. Pasquet, Eric; Bourdon, Estelle; Kalyakin, Mikhail V.; Cibois, Alice (2006). "The fulvettas (Alcippe, Timaliidae, Aves): a polyphyletic group". Zoologica Scripta. 35 (6): 559–566. doi:10.1111/j.1463-6409.2006.00253.x.
  13. Gill, Frank; Donsker, David (eds.). "Sylviid babblers, parrotbills & white-eyes". World Bird List Version 5.2. International Ornithologists' Union. Retrieved 29 May 2015.
  14. Aymí, R.; Gargallo, G. "Dartford Warbler (Sylvia undata)". In del Hoyo, J; Elliott, A.; Sargatal, J.; Christie, D.A.; de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions. Retrieved 29 May 2015.(subscription required)
  15. Mayr, Ernst; Cottrell, G. William, eds. (1986). Check-list of Birds of the World, Volume 11. Cambridge, Mass.: Museum of Comparative Zoology. pp. 285–286.
  16. Latham, John (1787). Supplement to the General synopsis of birds. London: Printed for Leigh & Sotheby. p. 287.
  17. Hartert, Ernst (1910). Die Vögel der paläarktischen Fauna, Heft 1. Berlin: R. Friedländer & Sohn. p. 602.
  18. Shirihai, Gargallo & Helbig 2001, pp. 281–282.
  19. Mason, C.F. (1976). "Breeding biology of the Sylvia warblers". Bird Study. 23 (3): 213–232. doi:10.1080/00063657609476506.
  20. Snow, D.W.; Perrins, C.M., eds. (1998). "Dartford Warbler Sylvia undata". The Birds of the Western Palearctic, Concise Edition, Volume 2. Oxford, United Kingdom: Oxford University Press. pp. 1288–1290. ISBN 0-19-850188-9.
  21. Bunyard, Percy F. (1914). "On the breeding habits of the Dartford Warbler" (PDF). British Birds. 7 (8): 214–219.
  22. "Dartford Warbler Sylvia undata [Boddaert, 1783]". British Trust for Ornithology. Retrieved 1 June 2015.
  23. Bibby, Colin J. (1979). "Breeding biology of the Dartford warbler Sylvia undata in England". Ibis. 121 (1): 41–52. doi:10.1111/j.1474-919X.1979.tb05013.x.
  24. Bibby, Colin J.; ‘Dartford Warblers in England’; British Birds, 72 (1979); pp. 10–22
  25. "BirdLife International 2012 Sylvia undata". IUCN Red List of Threatened Species. 2012. 2012. Retrieved 5 June 2015.
  26. "The state of the UK's birds 2017" (PDF). Joint Nature Conservation Committee. pp. 30, 39. Retrieved 14 December 2017.

Sources
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