It's not often you do a search on a scientific subject and come up with a journal from 1888, but people were puzzled by this mystery for a while: Female birds, usually once they've reached a sufficiently advanced age, can suddenly grow male plumage and take on male behaviors.
I read in a book that, seemingly at random, female birds could start growing male plumage. Intrigued, I did a quick search for why, and got a journal article entitled, "On the Occasional Assumption of the Male Plumage by Female Birds," which dated back to 1888. That article, which I found a little old-fashioned, started out by sniffing at the quaint old-fashioned conceits of another article written in 1780. Obviously, this question has gone back a long time, puzzling many scientists.
Some of these early scientists were confused by a red herring — the fact that sometimes female birds developed patches of male plumage. Some birds were completely divided, one half of them being male and one half of them being female. This condition, known as bilateral gynandromorphism, is the result of genetic mosaicism. For whatever reason, a clump of cells with male chromosomes gets attached to a clump of cells with female chromosomes and knit together into one animal. This gave scientists a lot of information that unfortunately was completely misleading. The sudden appearance of male plumage on female birds is not genetic at all.