I have a strange phenomena, or so it seems. My pair of Red-wing Blackbirds went to 3 a few days ago. One, I'm assuming the male, has stunning feathers, and he is always fluffing them up to show them off. The other 2 I'm guessing are females. Their wings aren't as brightly colored and they don't exhibit any of the puffing and preening behaviors. It just seems odd to see them as a threesome. I've not seen any trace of another male bird.
Menage A Blackbird?? LOL!
Now that I think about it, red wings are a 'flocking' type of bird, so maybe a male will breed with more than one female during a season, while non-flocking birds like cardinals have single male/female pairings.