For the Birds Radio Program: Dr. Ruth of Ornithology Pt. 3. How birds do it
This week I’m producing For the Birds in my Dr. Ruth of Ornithology capacity. I started out talking about the unique equipment birds have—both the male and the female have a cloaca—sort of the back door vestibule of the house. Male birds are lacking exactly the equipment that male humans are wont to describe in linear measurement terms—some males develop what’s called a cloacal protuberance, but that’s a temporary anchor and nothing more. Since most of the year birds’ sex organs shrink to just about nothing, it takes time for the females’ single ovary and the males’ internal testes and that protuberance to grow and become functional. But finally, we reach the point where two 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 – maybe their Mallards and haven’t had to do anything at all—but now the Big Moment arrives!
The male flutters his wings in eager anticipation, and this time the female doesn’t flitter off dismissively, saying she has a headache – she actually flutters her wings back at him!
So he hops aboard her back, and she twists 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.
We have lovely myths about eagles mating in the sky, but if any eagles tries that, gravity would quickly hand them a Darwin Award. That talon-locking in the sky is a courtship ritual—the actual act of mating takes place on a sturdy branch or on nice solid ground. Swifts are the only, or one of the only, birds believed to actually mate in the sky.
The act of mating is rather dangerous for birds that have sharp, powerful talons—leastwise for the female. If the male on her back starts thinking about his stomach, even for a split second, it could be a fatal case of bye-bye birdie. Fortunately, female hawks are larger and stronger than males, and that’s especially pronounced in those species that eat other birds, so she can give him a long hard stare and he’ll be very careful.
Anyway, once the sperm are deposited they swim, as sperm are wont to do, heading up her oviduct. Meanwhile, back at the ranch, she’s ovulated one ovum—that’s the whole 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 cloaca, 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.