St. Valentine’s Day as we know it is largely the brainchild of greeting card companies and Geoffrey Chaucer. In his “Parliament of Fowls”, the English poet details the events of the 14^th of February, when the beasts of the air gather to choose their mates. Birds, it turns out, have been perfecting the art of courtship long before Valentine’s Day was a twinkle in Hallmark’s eye.

A male Indian peafowl (Pavo cristatus) displays his brilliant plumage.

Love often inspires demonstrations that appear quite mad. Case in point: the peacock’s tail. Darwin himself was vexed by this appendage, which appears to be the result of temporary evolutionary insanity. Blazing colors advertise the peacock’s location to his predators as well to his paramour. Its weight hinders escape. Why would nature produce such a beautiful death sentence?

The answer, as Darwin found, lies in a special corollary to “survival of the fittest”: sexual selection. In retaining his splendid tail, the peacock gains more by attracting females than he loses by decreasing his own chances of survival. The opportunity to pass on his genes motivates him more than ensuring his own safety.

Female (left) and male (right) satin bowerbirds (Ptilonorhynchus violaceus) in a courtship ritual.

But success involves more than length of your feathers. Sometimes, the most ostentatious display isn’t the smartest strategy. During courtship rituals the male satin bowerbird builds little bowers, shaped like huts, out of twigs.   Females make a round of visiting all the males, squatting in each hut in turn. Meanwhile, the male then runs back and forth, fanning his feathers  and emitting a pulsing cry. The display is aggressive, though, and if the male overdoes it, the female will flee.  Not unlike their human counterparts, male bowerbirds walk a fine line between advertising their wares and killing the mood.

Dr. Gail Patricelli of the University of California at Davis, who studies the birds, used a novel mechanism to gauge a male’s social sensitivity- a robotic female bowerbird.  She placed the “fembot”in a bower and manipulated the controls to make the robot crouch higher or lower. Real females will adopt a lower stance when they are more receptive to mating.  A higher one signals that she is nervous.  Some males scaled back their displays when the fembot showed reluctance, while some plunged on regardless.  Dr. Patricelli compared the behavior of the male bowerbirds towards the robot to the number of successful courtships with real females.  The results, published in a supplement to the Journal of Ornithology, suggested that males who best tuned the intensity of their displays to match the fembot’s mood would later have the greatest mating success with non-robotic partners.

Sometimes, courtship becomes too complicated for one bird, and he needs a little help from his friends. Taking a cue from Facebook, David McDonald from the University of Wyoming mapped the social network of a subpopulation of long-tailed manakins. In this species of songbird, the males have a unique arrangement. A pair of unrelated manakins will team up to perform a kind of backwards leapfrogging dance for curious females. However, the pas de deux only pays off for one of the partners. The younger male never mates. He’ll only have the opportunity for romance once his older partner dies.

Long-tailed manakins (Chiroxiphia linearis) performing a courtship dance.

The dance of the manakins seems to defy evolutionary sense. Actively assisting a genetic competitor isn’t exactly Darwinian. Manakins, however, gain an advantage by playing wingman. In the biological journal of the Royal Society, Dr McDonald reports that those males who had the largest number of connections to other males eventually had the greatest mating success when they became alphas themselves. McDonald suggests that in pair courtship, females are rating the overall performance rather than paying attention to the individual. “It’s the restaurant,” he says, that garners a good reputation, “not the chef”. Sexual selection might appear to make fools of birds and men, but it’s a foolishness that’s finely tuned for romantic success.

Video by Bo Zhang and Roxanne Palmer

The lightbulb image for this post is being used under a Creative Commons license.