Published online 28 December 2001 | Nature | doi:10.1038/news011227-9

News

Perch affects birds' pitch

Birdsong makes best use of forest acoustics.

<mediar rid='m3'/>

Birds tailor their songs to the height of their perches, say researchers. Different species' songs seem to make best use of the acoustic characteristics of different layers of the rainforest.

Species that sing close to the ground have slower, lower-pitched songs and use a narrower range of pitches. Sound does not travel as far, or as clearly, near the ground as it does through open air. On the forest floor, a slow song is easier to hear and recognize than the faster, higher-pitched songs of birds that broadcast from the trees.

Like composers, birds craft their music to suit their venue, says ornithologist Erwin Nemeth of the Austrian Academy of Sciences in Vienna, leader of the team that made the discovery. "There's some music that works in cathedrals, and other music that works only in jazz clubs," he says.

Just as an echoing church would turn a rapid sax solo to sound soup, so the reverberations in dense undergrowth render a high-pitched twitter unintelligible.

Sounding out

Nemeth and his colleagues recorded the songs of five species of antbird living in the Venezuelan rainforest. These small birds produce a series of simple chirps that is innate rather than learned.

Both sexes sing, sometimes in duet, to defend their territories. Different species sing from different heights - where they also hunt food - ranging from just above the ground to 20 metres or more up in the canopy.

Nemeth's group replayed their recordings at different heights and measured how far and how clearly they carried.

“Looking at the effect of habitat on birdsong is very difficult”

Kate Buchanan
University of Cardiff

The slower-paced, lower-pitched songs of the thrush-like antpitta (Myrmothera campanisona) travelled best at ground level, where this bird dwells.

Higher in the forest, the results were not so conclusive. Other considerations, such as singing dextrous songs to impress potential mates, could influence song structure in this more favourable acoustic environment, the researchers argue.

"It's a nice experiment, but there are some problems with comparing between species," warns birdsong researcher Kate Buchanan of the University of Cardiff. Differences in behaviour may also influence song, she says.

"Looking at the effect of habitat on birdsong is very difficult," explains Buchanan. Ideally, she points out, one would want to study a single species in two different environments, such as forest and grassland.

The acoustic properties of other birdsongs also seem to be adapted to fit their circumstances. The alarm call a blue tit makes when menaced by a sparrowhawk is hard to locate in space, and is in a frequency range that hawks do not hear well. 

University of Cardiff

  • References

    1. Nemeth, E., Winkler, H. & Dabelsteen, T.. Differential degradation of antbird songs in a Neotropical rainforest: adaptation to perch height? Journal of the Acoustical Society of America 110, 3263 - 3274 (2001). | Article | ISI |