I actually haven't seen Portlandia yet, though I think I'd like it.
I belong to a loose craft collective here (some sewing, some of this, some of that) and the "Put a bird on it" video made the rounds shortly after it came out since so many of us seem to be bird-lovers.
I think you're right about birds, plus they are so colorful and varied. They're more like flowers than other animals almost.
Fruits, flowers and birds seem to be the perennial decorative features (and sometimes all three).
(Thanks for the compliment! I love making those birds, it's an amazing pattern. That was the first one, I don't like the weird bump on his head, got better at it later. I especially like the one I made out of a vintage linen tea towel.
Edit: here's the pattern if anyone else is interested: