The birds and the bees, part one

Okay, so you have been told about the birds and the bees. But do you really know how the birds are doing it? (Sorry, bees, we'll talk about you another time. Okay?) Because when you begin to think about it, there often are at least two points at which you begin to wonder: How do birds actually do it?

Passerine penisless passion

The first thing that may puzzle you is that most birds don't have a penis... (Oh boy, and we'll definitely have to talk about those that do at some point!) So how do you get sperm into a female cloaca without a penis? Of course, if you are female you immediately know the solution for ejecting fluid into something: Simply sit down! And that's more or less it. The act is called cloacal kiss and usually is really quick. And if you want to see that in a little movie, just go here. The actual act takes place at second 36 in case you missed it the first, second, or third time! Aaaaand in case you wondered: the picking of the cloaca probably is to remove sperm from the last guy.

So overall, bird sex is a bit like the movie cliche of a high-school ball date: The guy tries to impress her by his dancing, then does some clumsy foreplay and just as she is willing to mate and allows him to get really close, the very moment their genitals touch, everything is over already...

Okay, but now for the real puzzle, the one students actually ask almost every semester in our developmental biology course: How does a sperm fertilize a bird egg? I mean - it cannot go through the shell, right? Well, to cut a short story, even shorter: It doesn't. The actual ovum (the egg cell) is produced in the ovary and then filled with yolk, from which the chick is later fed. Then the ovum is fertilized, the egg white is added as a kind of aquarium for the embryo to grow into and finally the shell is added - with colorful sprinkles in the outer layer in some species and with a bubble of air for gas exchange. So the next time you enjoy a breakfast egg (most of which are not fertilized actually), take a moment to marvel at the miracle of the bird egg.

Simplified origin of a bird egg