WHEN the time comes to choose her mate, a female long-tailed manakin pays no attention to the real estate he owns, the size of his larder, or any other trappings of bourgeois respectability. She opts for art and chooses a male who can sing in tune and shine on the dance floor.
The mating habits of long-tailed manakins, which live on the mountains of Costa Rica, are among the oddest of any bird, says David McDonald, a behavioural ecologist at the University of Florida in Gainesville. Adult males pair up in stable partnerships that can last for years. Together, the two males spend hours each day singing a duet to woo females. Once a potential mate arrives, the partners begin an elaborately choreographed dance in which they leapfrog over each other and fly in a distinctive, laboured manner that McDonald calls 鈥渂utterfly flight鈥�.
If the female deigns to mate, the honour goes to the senior partner, or alpha male. The junior, or beta male reaps his reward years later: when the alpha dies, the beta inherits his mentor鈥檚 alpha status, and recruits his own apprentice.
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But how do females decide which dances to watch? McDonald and his colleague Jill Trainer of the University of Northern Iowa in Cedar Falls recorded the duets of seven pairs of males to see if their songs held any clues. The songs sound like the word 鈥淭oledo鈥�, with the second syllable sung one and a half tones higher than the other two. Trainer analysed sonograms which detailed the precise harmonic content of each song and matched the results with McDonald鈥檚 data on how often females called on each of the seven partnerships.
The researchers found that pairs of males who sang in tune 鈥� that is, where each bird鈥檚 song most closely matched its partner鈥檚 in pitch 鈥� got the most visits. 鈥淭he best analogy would be something like two violins. It鈥檚 a richer sound when they鈥檙e better in tune,鈥� says McDonald. Female manakins proved to be discerning music critics, preferring the best matched duet even when there was no noticeable difference to the untrained human ear (Behavioral Ecology and Sociobiology, vol 37, p 249).
Manakin singers improve with practice, says McDonald. This means females who visit the best singers and mate with the best dancers, another display that presumably requires practice, are selecting males who are long-lived and therefore possess good quality genes.
By requiring males to compete for their favours with song and dance, almost all female manakins end up mating with the handful of males that star in both tests. Indeed, of the 80 males on McDonald鈥檚 study site, just five accounted for more than 90 per cent of all the copulations in ten years. 鈥淭he guys who are in good tune are also singing the most: And they dance the best,鈥� says McDonald. 鈥淭he really successful males are good at everything.鈥�