Blunt-winged Warbler (Acrocephalus concinens, 钝翅苇莺) is a strange bird. There are two populations, one breeding in eastern China and the other breeding west of the Himalayas in northern India, Pakistan and Afghanistan. In some places it appears to prefer reedbeds and in other places it prefers dry, scrubby hillsides. For a time some people suspected that the two populations may be two different species, however research has shown that they are, in fact, one.
In Beijing, Blunt-winged Warbler is a scarce breeder and passage migrant. It used to breed at the Summer Palace until the late 1980s/early 1990s when the reedbed was “sanitised”. I have found migrants at Yeyahu NR twice in spring and once in autumn. In mid-May I found another singing bird in Hebei Province at the Baer’s Pochard breeding site and Paul Holt found at least 11 singing males at the same site a few weeks later… (clearly, they hadn’t yet arrived when I was there…. cough).
Before I saw this species and Manchurian Reed Warbler (Acrocephalus tangorum, 远东苇莺) I wondered how easy they would be to tell apart. Having now seen both, they are relatively straightforward to separate. Here is a comparative image of the head pattern and underparts of both species (both images taken this Spring).
Note the supercilium, which reaches well behind the eye on Manchurian and is barely visible behind the eye on Blunt-winged. Also, note the dark upper border to the supercilium on Manchurian, lacking in Blunt-winged. Other features to note are the obvious pale throat bordered by the buffy upper breast on Manchurian. On Blunt-winged, the pale throat is not as obvious, merging in with the pale upper breast. The darker cap with perhaps darker overall upperparts may be a useful feature, too. The bill is slightly sturdier in Manchurian with an all-pale lower mandible.
I’d like to write a similar post about Black-browed and Streaked Reed Warblers… but first I need to find one of the latter! Wish me luck……