Anybody? . . . ANYbody? . . . Bueller?
Because it is, and always has been. Within bird species, there are difference "races," and they are described that way. No pity-party CNN segment required.
Regional isolation of any creature that successfully reproduces is going to get more homogeneous with itself over many generations. Forty or more generations on, more of the individuals in the group are going to share more genes with each other than they will with members of the same species outside the isolated group.
But if you're a devout Lefty, you don't believe in genetics at all. Genetics makes it harder to lie. Just ask Lysenko.
LEFTIST/PROG/LIBS don’t DARE to believe in genetics!
Believing in genetics means you can prove beyond any doubt WHO IS A MAN and WHO IS A WOMAN!