Science

13 Mar 09

Female antbirds ‘block out’ the notes sung by their partners resulting in a more complex acoustic display.

Female birds faced with competition from an unpaired female rival can ‘jam’ the songs of their own mates, who then respond by singing more complex songs to avoid interference, Oxford University scientists have discovered.

The findings, reported in Current Biology, are based on a study of the Peruvian warbling-antbird (Hypocnemis peruviana), and provide the first evidence that signal jamming is used within long-term partnerships.

Animal duets are often precisely coordinated, but there has been a long-running debate about whether they are purely cooperative, or whether they reflect conflicts of interest. The Peruvian warbling-antbird offers an ideal framework for studying this question because on one hand males and females sing together to defend shared territories, and on the other males sing ‘solos’ as part of attracting a mate.

‘Single females are a threat to paired females because they increase the likelihood that males will cheat on their existing partner, or abandon them in favour of a new one. We know that divorce, in particular, is common in antbirds. The presence of single females therefore leads to a kind of acoustic battle in which males and females have rather different priorities,’ said Dr Joseph Tobias of Oxford’s Department of Zoology who led the work with Oxford colleague Dr Nathalie Seddon. 

To demonstrate this conflict, and to show how it affects singing behaviour, researchers tracked 17 pairs of antbirds in the Peruvian rainforest and did two experiments. The first involved playing them sounds of a rival pair invading the territory, and the second involved playing songs of a single female.

Dr Tobias said: ‘Resident pairs faced with a rival pair responded in concert with a simple, precisely coordinated duet. However, when they heard a single female, the coordinated duet broke down as paired females attempted to jam – effectively to ‘block out’ – the notes being sung by their own partners. Males then countered this strategy by changing their songs in an attempt to avoid interference, resulting in a more complex acoustic display.’

These findings demonstrate that animal duets can be cooperative or manipulative, depending on context. They also provide the first evidence that individuals singing communally try to avoid being jammed, suggesting a simple mechanism that tends to increase both the temporal coordination and complexity of duets. The research helps to explain the recurrent evolution of complex communal signals in many lineages of birds and social primates, and may provide a useful clue to the origins of human music.

A report of the research, ‘Signal jamming mediates sexual conflict in a duetting bird’, is published online in Current Biology.

Below: Listen to a sound file containing antbird duets: (1) two typical coordinated male-female couplets, followed by (2) signal jamming and jamming avoidance.