Ninety-seven percent of bird species don't grow penises. But why?
A 2013 study that compared chickens (who don't have penises) with ducks (whose penises are "large and elaborately coiled," according to one description) found that a sort of cell suicide, called "programmed cell death," is to blame.
“Evolution comes down to reproductive fitness," Martin Cohn, a University of Florida biologist, told the Los Angeles Times. "So it’s remarkable that a group of animals would eliminate a structure that’s so important for reproduction.”
A theory as to why birds lost their penises is that female birds may have preferred it, since, as The Scientist put it, birds of this disposition "are less capable of unwanted advances and thus give female birds more choice in which males father their young."
Birds Get Romantic With a "Cloacal Kiss'
For those birds without penises, mating takes the form of the "cloacal kiss."
The cloaca is an orifice found on the rear of both bird sexes. It serves a whole bunch of functions: pooping, peeing, egg-laying, and sperm ejection. When it's time to mate, the cloaca will swell. The male and female birds will then rub their swollen cloaca together, once the male hops atop the female and the female moves her tail out of the way. The ensuing "kiss," or sperm transfer, is, generally speaking, vanishingly brief.
Horny Male Birds Put On A Great Show
For birds whose mating requires female consent, males may engage in elaborate mating rituals to lure prospective sex partners. This excellent video of a superb bird-of-paradise -- a species whose males face stiff competition for female partners -- was put together by Cornell's Birds-Of-Paradise Project, which also has a great fact sheet about these birds' female choice.
Ducks Have Penises That Are Shaped Like Corkscrews
Duck penises are long counterclockwise twists, while similarly-shaped duck vaginas twist in the opposite direction. The clockwise-shaped vaginas are, according to politically controversial (though not for the reason you might think) ornithological research, helpful in preventing nonconsensual sex from leading to fertilization. One scientist described the development of features that would either enhance or diminish the probability of forcible duck sex leading to insemination as an "arms race."
Some Female Birds Are Polyamorous
You'll hear the statistic that some 90 percent or more of birds are monogamous. More nuanced accounts of bird monogamy suggest that even among our "socially monogamous" feathered friends, it is quite common for DNA testing to reveal the presence of "illegitimate" chicks in the brood.
In other words, bird society is really interesting. Wattled jacanas -- like the bird in this photo -- are explicitly polyandrous, meaning the female birds take on multiple male lovers. Female wattled jacanas mate with many males, who then incubate the eggs and raise the chicks, even when paternity isn't clear. This setup is a rare state of affairs, as it were, both in and out of the bird world.
Good Thing Baby Penguins Are Sooooo Cute After That Long Incubation
Emperor penguins have one of the bird world's longest incubation periods. Females lay one egg in May or June (wintertime in Antarctica), then skedaddle to look for food. The male penguins incubate the eggs -- on their feet, not eating, in temperatures that can go down to -76 degrees Fahrenheit -- for 65-75 days. Moms come back and regurgitate the food they've hunted while away to feed their newly-hatched chicks.
Queen Bees Take A 'Mating Flight' Early In Their Lives, Late In A Drone's Life
A week into life, new queen bees go on "maiden flights" (also called "mating flights," "virgin flights" and "wedding flights"). While they're flying about, they will mate with a dozen or so male bees, called drones. Each drone sticks his endophallus, or bee penis, into the queen's sting chamber (that's not a euphemism; that's what it's called). Then that's that for the drone -- some describe bee mating as a drone's "sexual suicide" -- but just the beginning for the now-inseminated queen.
Drones Have No Fathers
There are three kinds of bees in a hive: a queen, worker bees (who are female) and drones (who are male, and make up a small percentage of the hive population). Drone bees are produced when a queen bee lays unfertilized eggs. That's right, unfertilized eggs -- which means that drones, whose main purpose is to mate with the queen and then die, are themselves fatherless.
Regicide Is A Fact Of Life For Bees
During her mating flight, the queen bee will mate with lots of drones. She'll then store their sperm inside her body for the rest of her life (up to a couple of years), laying thousands of eggs -- fertilized and not -- to replenish the colony. Drones hatch from unfertilized eggs. Worker bees hatch from fertilized eggs; there are more worker bees than any other type in the hive, and they do almost all the work. Queen bees -- those are two queen bee larvae in the photo -- also hatch from fertilized eggs, but ones that have been fed royal jelly by workers, once the original queen's fertility is failing. The first queen to hatch will often kill the other developing queens. Queens are killed in various other circumstances as well; when worker bees kill a queen bee as a group, it's called "balling."
And, look, let's not get prudish now. Here's a video of sperm being collected from a drone. We asked the scientist who made this video, Peter Schley, if drones whose semen is procured in this manner also have to die right away.
Bad news for the bees: he said yes, that both natural and manual copulation "tear important nerves."
It's fascinating, still, though might not put you in the mood for exploring the human version of the birds and bees -- or for honey:
This piece has been updated with comments from Peter Schley.