For those with more experience with the medium terns than I have, a question.
This last weekend, Common Terns were observed at both Mann Lake (6) and Swallows Park (12).
IDing these medium terns is difficult at best and I have tended to rely on flight photos to help me.
Does anyone have enough experience with these to know when most/all adult Forster's Terns will have made the change to basic (non-breeding) plumage?
I have photos of Common Terns in adult breeding plumage as late as 17 Sept.
Life would be easier if we had a good date for when all adult, breeding plumage birds were Commons.
I know from personal observation and Kenn Kaufman's Advanced Birding that Commons retain this plumage longer than Forsters, but cannot find a date for when Forster's will have made the change to basic.

Keith Carlson
Lewiston