SAN FRANCISCO--The Pavarottis of the canary world can drive a female wild by singing certain special notes. Now scientists have learned what makes these "sexy syllables" so alluring: Virtuoso canary singers have mastered a tricky vocal technique, which may indicate their overall robustness.
Birds sing to attract mates. But why females prefer a particular song has been a puzzle. Although there's evidence that complex and frequent songs are more attractive, a recent idea suggests that certain notes are the key to seduction. "Sexy syllables" in canary song were first identified in 1995 by ethologists Eric Vallet and Michel Kreutzer of the Université de Paris X in Nanterre, France. When males sang certain trills, or when the trills were played on tape, caged females assumed postures inviting copulation.
Now neuroethologist Roderick Suthers of Indiana University in Bloomington has joined the French team, along with Université de Paris X graduate student Aurélie Tanvez, to determine what makes these syllables so sexy. Unlike our voice box, the avian vocal organ (the syrinx) has two tubes, instead of one, surrounded by sets of muscles--allowing birds to produce two sounds independently. The researchers monitored muscle activity and air flow through the syrinx with implanted sensors while the canaries sang. By matching sound qualities such as pitch and frequency with the bird's physiology, they could determine how it sang the different syllables. The team found that unlike most notes, sexy trills required extraordinarily fast and coordinated alternation between the left and right sides of the syrinx, more than 16 times a second.
The team hypothesizes that a male's ability to pull off such coloratura may indicate its overall vigor; the notes may be "honest indicators" that females can use to select high-quality mates. Suthers presented the findings on 3 November at the symposium "Nature's Music: The Science of Bird Song," in memory of bird song pioneer Luis Baptista of the California Academy of Sciences, who died unexpectedly last year.
The work is both novel and intriguing, says Sarah Collins of the University of Nottingham, U.K., a fellow symposium speaker and a specialist in bird song and mate choice. It's reasonable that the sexy syllables could be honest indicators of male quality, she said--but whether they might reflect a bird's genetic merit, or simply its current condition (due to what it's eaten recently, for instance), remains to be tested.