ajohn

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

ajohn

Thanks Paul for clarifying the situation with iris colour. I thought maybe it was age-related, as pictures of juvenile Common Cuckoo on OB do all show a dark iris.
It seemed strange to me, though, that all pictures of adult Common showed a yellow iris, but those on Oriental all seemed darker (except perhaps this one http://orientalbirdimages.org/se ... _ID=&pagesize=1). Perhaps just coincidence?