Many thanks Ian that’s a very comprehensive and most interesting reply and opened up a whole new level of birding for me. My initial, basic thoughts after reading would be for the opportunity for observers to count the number of paler males against the number of strongly coloured male birds which might perhaps give an indication of the health/breeding success of a population? Just a thought.
Many thanks again,
Matthew.
As an aside, I thought that the hedgerow berry harvest was poorer last Autumn than previous years, or perhaps just earlier than usual.