Birds with rhythm sing scary harmonies
Pairs of magpie-larks use choral skills to intimidate rivals.
Pairs of Australian magpie-larks (Grallina cyanoleuca) that sing in tune and in tempo are more threatening to rivals whose territory they move in on than pairs that can't quite get their twittering coordinated.
Michelle Hall from the Max Planck Institute for Ornithology, working at the Australian National University in Canberra with Robert Magrath, listened closely to the shared songs of breeding pairs of the birds. The most coordinated magpie-lark pairs sang alternating notes of the song in a way that, to an untrained ear, gave the impression of being a single voice. Uncoordinated pairs don't get the alternation quite right and produce overlapping notes.
Hall then played recordings of coordinated and uncoordinated songs within the territory of 12 magpie-lark pairs. The most closely coordinated songs provoked the most aggressive territorial defence response from the male birds being 'invaded'. These birds who thought their territory was under threat responded by singing more in return.
The research raises a number of questions, not least what is so intimidating about a coordinated song, says Peter Slater, an expert in bird duetting at the University of St Andrews, Scotland. "They're producing a song that might as well be produced by an individual," says Slater. "High coordination might be an indication that these are rivals not to be messed with," he suggests.
There is hope for pairs that aren't well coordinated: Hall found that as couples spend more time in each other's company their coordination improves. Again, the reasons for this are not yet known, but could be to help coordinate reproductive activity, or could be to ensure that the birds are motivated to continue acting collectively. "It's a private language, what exactly they're up to is not clear," Slater says.
- Hall M. L. & Magrath R. D. Curr. Biol., 17 . R406 - R407 (2007).