When it comes to courtship, members of the Aves class are a class unto themselves. They dance like Michael Jackson and sing like Barbra Streisand. They work hard to sustain their relationships, even after mating. They actually tidy their homes before inviting someone over.
And while their flirting strategies are a bit, well, unusual — blue-footed boobies try to attract partners by waggling their aquamarine appendages — they're certainly more creative than the pickup lines preferred by humans.
Consider the “sky dance” of the American woodcock. On spring evenings just before dusk, a male woodcock will find a spot at the edge of the forest and issue a resounding, buzzy “peent.” If he manages to catch a female woodcock's attention, he'll take to the skies, soaring upward in a huge, wide spiral, making a twittering sound as it riffles his wings. Then he'll drift back to the earth like a leaf, zigzagging to land in exactly the spot from which he launched.
It's possible to watch this display if you live on the East Coast, said Sara Kaiser, a behavioral ecologist at the Smithsonian Center for Conservation Genomics. Just head to a wooded area bordering open ground and listen for the male birds' characteristic “peent.”
“It's really spectacular,” Kaiser said.
But by avian standards, even those guys are slackers.
The red-capped manakins of Central America gather at courtship assemblies called leks, which Kaiser compared to night clubs. “You have all these males that are trying to show off and attract these females,” she said.
In a lek, up to five male manakins pose on a tree branch and shuffle back and forth as though moonwalking. They pivot to flash their yellow inner thighs, snap their wings and circle around their perch while a female manakin watches. If she's unimpressed by what she sees, she'll fly to a new lek — like club-hopping, minus the bad music and floors sticky from spilled beer.
The satin bowerbirds of Australia go the extra mile to attract a mate: Not only do the male birds do a special dance, but they perform it in elaborate stick structures adorned with objects in their favorite color — blue. When researchers try to mess with the birds' decorating scheme by sneaking in red objects, the male birds swiftly remove it before it's spotted by a potential mate. They know female bowerbirds would never make the mistake of going home with a guy whose place is less than impeccable.
Maria Servedio, a biologist at the University of North Carolina at Chapel Hill, loves the courtship dance of the hooded grebe — a critically endangered species found only on the windswept plateaus of Patagonia. Paddling across their high-altitude lagoons, they extend their necks back until their heads touch the water, then lean forward with their wings outstretched. Next they rush toward each other and bump chests like football players. Finally, they slap their webbed feet against the water until they're nearly standing, then dance over its surface in nearly perfect synchrony.
These elaborate romantic rituals are the result of sexual selection, the process by which organisms' mating preferences gradually shape the evolution of their species. When female birds have a slight preference for male birds with certain traits — guys with flashy plumage, a seductive dance, a tidy bower — they're more likely to have offspring who inherit both that preference and those traits.
“As the display evolves, the preference will evolve as well,” Servedio said. “You end up exaggerating selection of both until you hit these ridiculous displays and ridiculous preferences.”
But why would female birds have these preferences in the first place? One theory is that these traits suggest something about the male bird's evolutionary fitness: a brightly colored bird might be healthier, a good dancer, quick and dexterous; a guy with a beautiful bower clever enough to keep his house in order.
Biologist Roxana Torres of the National Autonomous University in Mexico has conducted experiments looking at what happens to blue-footed boobies that are aging, hungry or diseased and found that within 48 hours, their signature cerulean feet had turned a drab gray. This indicates bright colors are an “honest signal” of good health, and it is in female birds' best interest to see the bottoms of the male birds' feet.
Another theory argues that female birds prefer some traits despite their implications for fitness. If a male bird has made it through life with a trait that seems like a handicap — say, a peacock's absurdly long train — then he must be really good at all the other behaviors needed for survival.
Whatever the reason for their appeal, courtship rituals are not merely a ploy to win a chance at copulating. Many species, including hooded grebes, are in it for the long haul — male grebes will perform their dances even after mating.
“It seems like the male has already gotten the girl so why is he bothering?” Servedio wondered. “Obviously it creates a gigantic ruckus and takes a lot of energy, and predators might be attracted.”
She and others believe sustained courtship induces females to stay invested in the relationship, making it more likely their offspring will survive to adulthood.
I asked Kaiser if her research on avian courtship had convinced her that birds are just better at romance. That's when she dropped her bombshell: “Actually, I study cheating in birds.”
“It's a really important behavior, evolutionarily speaking,” she added.
Kaiser conducts research on songbirds that must migrate to their breeding grounds each year. For male birds, cheating — or “extra-pair copulation,” as Kaiser diplomatically put it — is a way to try to pass their DNA to as many offspring as possible. “The jury's still out” on benefits for female birds, she said, but it may also be a way for ladies in lousy relationships to seek better genes for their young.
Either way, Kaiser's research suggests birds of both sexes are more than happy to cheat when the opportunity arises.
“When a female is ready to lay her eggs all the males come out of the woodwork. They're there singing at the edges of their territories, trying to get her attention,” she said. “It's really funny.”