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How Do You Learn the Sex Secrets of Birds? Send in the Fembot
Considering that most of his comrades would die without ever mating, Dick was impressive.
He once pulled off 30 copulations in a single morning, 23 of them in as many minutes. Usually coy females were enamored with him. When other males got too close, he didn't trouble himself with long, drawn-out turf wars. Instead, with a brisk thwack, Dick repelled any intruders and got back to dancing. And he danced hard, for hours on end.
"Dick was a phenomenon, and we've never seen anything like it," said Gail Patricelli, a biologist at the University of California, Davis.
Dick was a greater sage grouse, a species famous for its elaborate, vaguely obscene mating ritual that occurs each spring across the West. And for decades, biologists have been trying to figure out what top males like him have that the others don't. In her approach to this problem, Patricelli has turned to partly taxidermied fembots. [Animal Sex: 7 Tales of Mating in Nature]
Bird's-eye view
"Most people who do taxidermy don't need their animals to move," Patricelli said. But she needs her robots to look and peck like the real thing.
Her latest creations, named Salt and Pepa, are made out of real female sage-grouse skins from local Fish and Game Department freezers. Their innards are fashioned out of circuit boards, model airplane parts, craft glue, cross-stitch mesh and a pair of Spanx.
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"I use whatever I can to MacGyver my way through it," Patricelli said.
With a remote control, Patricelli and her colleagues send Salt and Pepa in to infiltrate a group of ready-to-mate males in Wyoming. The robots aren't simply intended to collect gonzo footage of strutting sage grouse (though they do have cameras on board). They primarily allow Patricelli and her colleagues to conduct the type of playback experiments scientists have been using to study animal behavior for years. [The 6 Strangest Robots Ever Created]
And the males don't seem to mind the attention from decoys. They are not, after all, in a position to be choosy. (When there aren't any females around, the males sometimes try to mate with dried cow pies.) It's a female's market out on the lek, a flat clearing that's sometimes described as a singles bar for birds.
During mating season, the males assemble at the lek before dawn to perform their complex strut display. They swish their wings across their chests and gulp air into their esophaguses, inflating two heaving air sacs on their breasts and making a very unbirdlike pop-whistle-pop sound.
Females, for their part, are much more modest. They move around the lek, pecking at the ground to eat and sneakily shopping for potential mates.
"The old descriptions of what goes on at a sage grouse lek sound almost Victorian in their sexual definition of these aggressive males that are showing off and fighting each other, and the females that are being coy and shy," Patricelli said. "But it really does play out exactly like that. It's really hard to watch the females and not think that they're being coy in the sense of looking like, 'I just happen to be here. I'm not here for courtship.' But they could be foraging everywhere. They forage on the lek when they're interested in mating."
When a female does pick a mate, it's easy to miss the deed: a "cloacal kiss" that lasts just a few seconds, enough time for a male to pass off his sperm. Then the female goes on her way, back to her own nest, to incubate and take care of the young entirely on her own.
The majority of males, meanwhile, never get the chance to be fathers. Most females choose to mate with just a handful of top males, like Dick, that dominate the lek.
"For Dick, it's a great system," Patricelli said. It's not so great for other males — or for conservation biologists who want to prevent inbreeding among dwindling populations of animals. That includes the embattled greater sage grouse, which is a candidate for a federal endangered species listing.
"In a lekking species like this, where almost all of the females mate with the same two or three individuals, once the population gets very small and inbreeding becomes a problem, you really wish there was some way you could get the females to mate with all the males that are available," Patricelli said. "But evolution does not have the foresight to work like that."
Why so fancy?
The mysteries of sexual selection have plagued scientists ever since Charles Darwin laid out his theory of evolution. Stumped as to why male peacocks should have such an elaborate tail, Darwin famously wrote to his friend Asa Gray, "The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick."
Darwin figured that flamboyant traits, such as the peacock's tail, somehow helped males compete for mates. But there are still more nuanced questions that biologists have yet to answer: What exactly do male mating displays communicate to females? If a female just needs to know that the male is healthy, then why does she need to see such complex, energetically costly signals?
So far, scientists have gleaned a few of the traits that set successful male sage grouse apart: They produce good sound, they tend to have fewer scars on their air sacs, and they tend to have lots of hens surrounding them. Patricelli is interested in finding out whether the successful males also have better social skills.
"We know that sexual selection can favor things like the peacock's tail and bright colors and loud songs," Patricelli said. "But what about social interaction skills? What we can do with the robot is send her out there and have her give particular signals to the males. And then we can ask whether males that are more responsive to these female signals are more successful in mating with real females."
It's almost impossible to answer that question without a robot, she said, because during natural courtship, females tend to behave differently around unsuccessful and successful males.
Patricelli's team has been collecting an enormous amount of data out of leks in Wyoming almost each year since 2006. The team has sensitive microphones and HD cameras scattered around the lek to record audio and visual data that eventually gets (arduously) extracted in a lab. With all this information, the researchers hope to answer questions such as how the distribution of matings changes over time, and how that relates to food and energy resources available to the birds.
But the researchers don't always have the opportunity to keep up with specific sage grouse, like Dick, the male that swept their lek last year. Some birds are outfitted with colored leg bands and can be tracked from year to year. But other, un-banded birds, like Dick, only stand out by the pattern of their "butt prints," or the constellation of white spots on their tails, which changes each year after the birds molt.
"This year, there is a male on Dick's territory, and he is still the top guy," Patricelli said. "I think it's probably Dick, but we can't be sure. One way or the other, he is not dominating like he — or whoever it was — did last year."
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