The bird was singing, an amazing incongruity, the bright, sharp south-Chinese Seicercus sound in a tiny wood on the muddy Chinese coast. The golden warbler alighted on a branch for several seconds.
Grey-crowned Warbler is rarely seen this far east and is not covered in Mark Brazil’s Birds of East Asia. However the very good Handbook of the Birds of the World Vol. 11, which I can’t recommend enough to lovers of leaf warblers and golden spectacled warblers, has the info we need.
A monotypic species, S. tephrocephalus is said by HBW 11 to breed as close to Shanghai as Hubei. It is very similar in plumage and song to Martens’s Warbler S. omeiensis but unlike Martens’s has the eye-ring broken at rear. S. tephrocephalus is common to abundant in its normal range of south China and Southeast Asia, but it had never been recorded in Shanghai. The lack of records is probably owing not only to its scarcity but also to its difficulty in identification, particularly for birders unfamiliar with HBW 11.
Much of the wealth of info on Seicercus warblers in HBW 11 is the fruit of the research of Swedish ornithologist Per Alström, who wrote nearly all the Seicercus entries. Guangdong-based French birder Jonathan Martinez has also researched S. tephrocephalus and helped me with the ID of the Grey-crowned Warbler.
Here are the sound-recordings I made of Grey-crowned Warbler. The recordings and photos are of a single individual.
Grey-crowned Warbler 1/2, Cape Nanhui, Shanghai, 17 May (00:11; 1.2 MB)
Grey-crowned Warbler 2/2 (00:23; 1.7 MB)
After viewing the photos and listening to the recordings, Per wrote the following to the Shanghai Birding WeChat group:
“I agree with your id of Grey-crowned Warbler, mainly based on the song recording (songs and calls are by far the best ways to id Seicercus warblers). The photos look a bit off (e.g., eye-ring broken in front, which isn’t normally the case in any Seicercus, seemingly poorly marked lateral crown-stripes, no clear grey on crown [though that could be a photo effect], and dark-tipped lower mandible [only in Grey-cheeked W]).”
To sum up:
My research indicates, and Per Alström concurs: Grey-crowned Warbler Seicercus tephrocephalus
Grey-crowned has eye-ring broken at rear; my photos show eye-ring broken at rear. The songs I recorded most closely match the song of S. tephrocephalus.
Next-closest possibility: Martens’s Warbler (S. omeiensis)
Very similar to Grey-crowned Warbler but doesn’t have eye-ring broken at rear.
Also: Alström’s Warbler (S. soror); my recording has trills; distinctive song of Alström’s lacks trills. Bianchi’s Warbler (S. valentini) does not trill. White-spectacled Warbler (S. affinis intermedius) has eye-ring broken above eye, not behind.