I've seen other animals do this too- my finial opinion was that animals:
1) (reasonable answer) Like zebras they want to make a huge see of confusing patters or one huge area of color like buffalo so they group by color by choice
2) (also reasonable answer) they were purchased from different places or at different times are are two separate flocks.
3) (a possibility, bids see full color) Animals choose fitness by color, a healthy lion has a thick dark mane, a young, sick, or elderly male has a straggly or light-colored mane - so female lions choose thick and dark, then dark, then light and thick then light and thin for breeding reasons. Rats choose by color also, but will most often choose a mate of the same color as them or the 'wild type' color. Gorrillias and silverbacks - this list goes on and on.
4) (a joke) You have racist birds and should teach tolerance as soon as possible....