A belated record of some interesting willow warbler songs, which have resurfaced again this year.
Last year, throughout May/June I repeatedly heard mixed singing chiffchaff/willow warblers along the Lancaster canal near Galgate. Further inspection revealed two separate birds holding territory along a between the bridge at Galgate and the beginning of the Glasson Branch. I heard a third mixed singer on Lancaster Uni campus.
The songs were classic “mixed singing” (not song switching) because chiffchaff notes were inserted into a willow warbler phrase. From reading this seems to be increasingly common, although in most cases the chiffchaff phrase does not have quite the right rhythm/quality. The canal warblers were able to sing the chiffchaff phrases perfectly though.
I eventually photographed one of them, confirming that it was (as far as is possible to know in the field) a pure willow warbler (pale legs, strong eyestripe etc…). A recent article in British Birds described the rise of mixed singing in willow warblers and attributed it to the increase in chiffchaffs and simultaneous decline in willow warblers; willow warblers and chiffchaffs compete for resources in overlapping territories, and as willow warbler territories are increasingly surrounded by chiffchaffs, speaking “Chiffchaff” may help them communicate and compete.
This may well be the case in Lancashire. The CC:WW ratios reported in the British Birds paper were around 10:1, practically identical to the CC:WW ratios along the canal and on campus. Conversely, I’ve not heard any mixed singers at Clougha Pike or around Arnside + Silverdale, where the CC:WW ratio is more even.
I’ve heard a few reports of mixed singers this spring, and Josh has sent me a recording of one along the canal near Galgate this morning, so clearly it was not just a one off.
Keep your ears open
L : )
