The Marsh Warbler Acrocephalus palustris is a rare bird in Britain nowadays, much more so than it was as recently as the 1970s. The reasons for its decline remain a bit of mystery.
In the late-1970s and early-1980s when I was cutting my UK ornithological teeth, I can remember annual pilgrimages to Worcestershire I think it was, in search of Marsh Warblers. Or to be more precise I went in the hope of hearing them sing. In appearance they are much like a Reed Warbler but their song could not be more different: full of mimicry of both their English neighbours and species from their African wintering grounds, their repertoire was astonishing. And their choice of habitat also differed from their reedbed-favouring cousins; as I recall, extensive riverside nettle-beds were what they liked, with a low bush or Hogweed stem used as an occasional song perch.
Above: Marsh Warbler Acrocephalus palustris, photographed in Belarus. The song is complex, varied and full of convincing mimicry. Features that help identify a silent bird include: the extent to which the pale-fringed primary feathers project relative to the overall length of the wing (more so than in other species); and contrast on the various upperwing feathers.
Following a brief period when it looked like the species might colonise southeast England, Marsh Warblers have all-but disappeared as a breeding bird in Britain: from what I can tell, available records indicate that nowadays annual sightings of passage migrants and vagrants greatly outnumber prospective nesters. So it seems that for the time being and foreseeable future most birders will have to forego the pleasure of hearing a Marsh Warbler sing in Britain, and turn their attentions instead to migrant and vagrant birds, which are often silent.
Above: Reed Warbler Acrocephalus scirpaceus, photographed in Berkshire, UK. The familiar song is a rhythmic mix of chattering and grating phrases, some of which may be repeated a couple of times. Features that help identify a silent bird include: the extent to which the primary feathers project relative to the overall length of the wing (more than in Blyth’s, typically less than in Marsh); and the warm buffish brown upperparts.
With this in mind, I thought it might be useful to compare photographs of the two species, along with another superficially similar Acrocephalus warbler that makes a regular vagrant appearance in Britain: Blyth’s Reed Warbler. This is where digital photography comes into its own. My ageing eyesight means that these days I can see more detail in my digital images than I can through binoculars in the field – the camera records what my eyes fail to see. Furthermore, modern digital definition means that many details, once the realm of a ringer’s handbook, can be captured photographically without seeing the bird ‘in the hand’. But caution is the watchword with these three, superficially similar species: photographs are pointers to identification and are not necessarily foolproof.
Above: Blyth’s Reed Warbler Acrocephalus dumetorum, photographed in Latvia. The song is quite unlike that of a Reed Warbler, comprising repeated bursts of abrupt, rather harsh phrases; it is sometimes delivered after dark. Identification indicators include: the short extent to which the primary feathers project relative to the overall length of the wing (less so than in other species), making the wings look ‘stubby’; the rather uniformly coloured upperparts; and a supercilium that is striking and pale in front of the eye.