Gah, stop it! These images are killing our brain cells! x_x
Oh, and personally, since Birdo and Yoshi are so similar, I don't see why they couldn't love each other and even mate. It's like a dog and a wolf producing offspring - which isn't weird at all.
However, we still haven't solved the issue of what gender Birdo is, which makes the matter of species unimportant. I wonder if Birdo's creators even knew whether it was a he or she....