How useful is iris colour?
I've seen this quoted as a feature for the ID of Indian cuckoo (which supposedly has a dark iris).
Looking through the pictures on OB, it get the impression that adult Common has a yellow iris, similar to the colour of the eye ring. Iris seems to be a bit more variable in Oriental - some are dark (brownish), while others are paler (straw-colour) but still seem to be darker than on Common.
I don't know whether iris colour may be related to season or sex, or maybe individual variation. D
oes anyone know if this is a useful feature to look for?
Incidentally, the iris on the Ping Long bird looks dark, which could support the ID as Oriental/Horsfield's