Acrocephalus palustris/scirpaceus - ID

Marsh Warbler & European Reed Warbler / Kärrsångare & rörsångare

ID - BEST CRITERIA:

Identification of these species is a well known subject to many European ringers. Some individuals are readily identified while others (especially young birds in autumn) are difficult indeed. Always base the id on as many characters as possible. The quick-guide given here is far from complete, and more help is found in e.g. Svensson (1992) and Kennerly & Pearson (2010).
A. palustris / Marsh Warbler

Plumage:
  • Generally slightly paler straw coloured above (including rump), often with a weak olive tinge in fresh plumage. Differences less obvious in 1cy birds.
  • Tertials with rather pale buffish-olive edges.
  • Tips of PP with fine whitish fringes when not too worn.
  • Pale eye-ring looks concolorous to the supercilium.
Soft-parts:
  • Claws rather pale brown-grey above, only slightly contrasting to the yellowish underside.
  • Bill often rather thick, and tastefully short.
Wing-formula (according to Svensson 1992):
  • Notch/wing ratio: 0,125-0,160 in 2cy+ and 0,107-0,157 in 1cy.
  • Notch on P2: 8,5-12 mm in 2cy+ and 7,5-11 mm in 1cy.
  • For further aid, see Svensson (1992).
A. scirpaceus / European Reed Warbler

Plumage:
  • Generally slightly darker and warmer olive-brown above, often with a rufous colour to rump. Flanks and sides of breast often shows a slightly darker/browner hue.
  • Tertials with rather dark rusty edges.
  • Tips of PP with no, or just faint whitish fringes (but a few are white-tipped as Marsh).
  • Pale eye-ring often tend to 'stand out' compared to the slightly warmer supercilium.
Soft-parts:
  • Claws dark greyish above, contrasting to the yellowish underside (but a few are paler).
  • Bill often slender and longer looking.
Wing-formula (according to Svensson 1992):
  • Notch/wing ratio: 0,167-0,231 in 2cy+ and 0,144-0,200 in 1cy.
  • Notch on P2: 11-15 mm in 2cy+ and 9,5-13,5 mm in 1cy.
  • For further aid, see Svensson (1992).
A. palustris, 1cy August. In 1cy the difference in colour may be less clear than between 2cy+ birds, and some birds are truely difficult to identify. Note the subtly paler straw colour above, and (less easily seen here) paler and cleaner flanks. Still, biometrics are crucial in the process. [CP46848]
A. scirpaceus, 1cy September. Compare to the bird to the left, and note the slightly overall warmer plumage and less contrasting tertials. [CV51017]
A. palustris (left) and scirpaceus (right), 2cy+ May. In adult individuals the differences in coloration above are more easily detected. Note the paler straw-colour in the palustris and the slightly darker and warmer brown plumage in the scirpaceus. [CS02495 and CS02496]
A. palustris (left) and scirpaceus (right), 2cy+ May. Note 1) the proportionally shorter and thicker bill in the palustris, and 2) the tendency for scirpaceus to show a more well set-of pale eye-ring. [CS02495 and CS02496]
A. palustris (lower) and scirpaceus (upper), 2cy+ May. Note 1) the rufous rump in the scirpaceus, and 2) the still present fine whitish tips to PP in the palustris. The appearant difference in tail length is only due to the lowered position angle in the palustris-tail. [CS02495 and CS02496]
A. palustris (lower) and scirpaceus (upper), mixed ages and seasons. The leg colour is generally darker in scirpaceus, but extensive variation (partly due to the age of the bird) makes the character dangerous to use. The colour of the claws gives better guidance: In scirpaceus dark above, clearly contrasting to the underside, while palustris are paler above, less contrasting to the underside. Note, however, that individual variation makes a few birds more difficult - for example the shown upper-right scirpaceus with pale claws. Note also the tendancy for palustris to show slightly thicker legs.
A useful chart from Falsterbo Bird Observatory, combining length of notch on P2 with wing-length (palustris in circles, scirpaceus without). See Walinder et al. (1988), available in PDF-format on Falsterbo BO's web page, for full comprehension.
More Acrocephalus palustris:
Ageing autumn
Ageing spring

Moult

More Acrocephalus scirpaceus:
Ageing autumn
Ageing spring
Moult
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