Birds That Sing Together Scare off Invaders

Anne Casselman
for National Geographic News

June 5, 2007

Many of us humans head in the other direction when faced with singers who can't carry a beat. But the opposite is true in Australian magpie larks.

For these birds, it's the more harmonious duos that frighten others the most.

Male birds react most aggressively to duets from pairs that are in tight tempo, a new study has found. This suggests that better synchrony in a duet signals a larger threat to other magpie larks.

Researchers played recordings of coordinated and uncoordinated duets in 12 magpie lark territories to simulate an "invasion" of other birds.

"An obvious human analogy ... is a human army," said study lead author Michelle Hall, currently at the Max Planck Institute for Ornithology in Germany. She did the research while at the Australian National University in Canberra.

"If you see an army marching and everybody's in time, you sort of wonder about how good they're going to be."

(See related: "Birds Change Songs to Suit Urban Life, Study Finds" [December 6, 2006].)

Singing the Same Tune

Pairs of magpie larks clock endless hours singing duets in their territories, which they occupy year-round. One bird sings a sound similar to "peewee" while its mate replies "wit."

The degree of synchrony varies widely across pairs. The researchers also found that the duet's coordination, and so its intimidation factor, improves the longer the two sings together.

"Individuals that get their act together" and sing in a extremely highly coordinated way seem to be signaling a commitment to each other in defending territory, said Peter Slater, a professor of natural history at St. Andrews University in Scotland, who was not involved in the study.

Lead author Hall said it's important for their survival and their reproductive success.

"Because if they don't have a territory, they don't have a partner, they can't breed, and they don't have a spot to find food," she said.

The study appeared today in the journal Current Biology.

Tropical Rhythms

A previous survey has suggested that about 200 birds species croon harmonious duets to defend territory, Slater said. The phenomenon is almost entirely restricted to the tropics, he added.

There, birds tend to stay put year-round and are almost entirely socially monogamous.

This way pairs are more mutually invested, and perhaps sing together to show it.

"It's in both of their interests to defend their shared territory and often their pair-bond as well," said David Logue, a postdoctoral fellow in the department of biological science at the University of Lethbridge in Canada, who was not involved in the study.

Dueting birds are more cooperative in their territory defense than non-dueting birds, said Logue, who has done research in the area.

The most impressive example comes from the plain-tailed wren, which sings in choruses of four parts.

(See related: "Tropical Wrens Sing Complex Tunes, Researchers Find" [August 8, 2006].)

"[Wrens] all join together and produce these extremely stylized and rather extraordinary songs," said Slater of St. Andrews University.

"It's like a war chant, really."

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