Even educated fleas do it...

Originally uploaded by Laura Erickson

But what exactly do birds DO? If you're trying to explain the birds and the bees to your children, get the answers from the Dr. Ruth of Ornithology, who explains the nitty gritty facts of life on her own blog. But she said we could quote it for you birds out there:

OK. Equipment on male birds: two testes, both internal (so avian sperm must be able to survive at very high temperatures, and they don't need to worry about their fertility if they jump on a bicycle now and then) that lead through the vas deferens to a chamber called the cloaca. The cloaca is sort of the vestibule entry into the whole house, with those two hallways to the testes, the ureters leading to the kidneys, and the large intestine. So it's very important for birds to poop before having sex, to clear out the vestibule before company arrives, so to speak, but since birds can poop at the drop of a hat (meaning on your head the moment your hat falls off) this does not represent any hardship.

Equipment on female birds: They have only one functional ovary (if they had two, and managed to ovulate through both, they'd end up with scrambled eggs inside), which is connected to the cloaca via the oviduct. During the nesting season, female birds usually ovulate about once a day. The ovary looks quite a bit like a teenie tiny cluster of grapes, only a couple of grapes are double the size of the rest, and one is HUGE. That is actually the whole yolk of the next egg to be ovulated.

So now the birds are feeling romantic -- maybe they're cranes and have been singin' and dancin' in the rain, maybe they're red red robins who've been bob-bob-bobbin' along -- and now the moment arrives! He flutters his wings in eager anticipation, and this time she doesn't flitter off saying she has a headache -- she actually flutters her wings back at him! So he hops aboard her back, and she's twisted her tail a bit to get the bottom to face the side, and he twists his tail to get the bottom to face the side, and their two cloacas meet in what ornithologists romantically call the "cloacal kiss." And a packet of sperm from him passes over into her cloaca. Then he flies off, she remains where she's sitting for a bit, and they each pull out a tiny little cigarette.

The sperm swim, as sperm are wont to do, and head up her oviduct. Meanwhile, back at the ranch, she's ovulated one yolk that morning, which is in the high reaches of the oviduct. One lucky sperm wins the race, and the rest go over into the pool hall and shoot a few rounds, hoping they'll have better luck the next day, and they sometimes do, because as I noted, they can survive warm body temperatures. As the fertilized egg works its way down the oviduct, the cells secrete the proteins that make up the albumen, and then secrete the calcium that will form the shell. And eventually, usually by early the next morning, the egg has reached the vestibule, which makes the female bird very uncomfortable and she heads for a nest (if her own isn't built, she'll take any port in the storm) and dumps that egg out. And it eventually hatches into another bird who will one day ask his parents to tell him where he came from, and they'll say, "The stork brought you," or "Toledo," depending on how much of a sense of humor they have.