Researchers Find History of Rainforest Told in Birdsong

"The songs of upland bower birds vary uniquely from place to place -- and are as culturally distinct from one another as regional dialects or languages are to humans," says Dr David Westcott, working on a Rainforest Cooperative Research Center project.

Dr Westcott's research is throwing an entirely new light on how the rainforest itself has developed over the last few thousand years.

"Birdsong is a learned trait -- a cultural attribute which the birds, who are great mimics, learn from their own community," he explains. "It varies greatly from one place to another -- and from it we can infer something about the history of the forest itself, and whether it has been interconnected or isolated."

"The golden bower birds of Mt. Edith on the Atherton Tablelands, for example, sing a completely different song from the birds of Mt Baldy just 20 kilometres away, which suggests that the two populations have been isolated from one another for quite some time."

Dr Westcott's analysis of the time, frequency and volume of birdsong up and down the 500-km extent of the tropical Australian rainforest has revealed not just slight, but often dramatic differences in song.

To human ears it may sound like music -- but to the birds, birdsong represents survival.

It decides not only differences between species, but also success in the unending battle over food, territory and mates. It may mark the distinction between survival and genetic death for an individual bloodline.

"From the song of a golden bower bird, we can pick its precise location -- whether it belongs to Mt Eden, Mt Windsor, Mr Baldy or Mt Spec. When we analyse the song, the sonograms or sound graphs are quite distinct."

Dr Westcott and colleague Dr Frederieke Kroon conducted an intriguing experiment, taping and playing the songs of bower birds from various localities to those at other places.

"If we played the local song, the birds got really aggressive. They looked as though they were ready to beat the hell out of the intruder.

"But when we played them the song from a different place, they just ignored it -- as if it had been the song of another bird species."

The picture that is emerging from Dr Westcott's analysis of birdsong is of the upland/cool rainforest as an archipelago of islands consisting of culturally-distinct bird communities, much like human communities speaking different linguistic dialects.

"This suggests that birdsong may be useful in documenting vegetation changes on short to medium time scales, or in documenting the impact of change on bird populations."

The upland birds that Dr Westcott studies are adapted to the cool, moist forest types that today grow on the mountain tops -- but which a few thousand years ago were probably far more widely distributed. With the gradual warming in the earth's climate since the ice sheets retreated, these areas have contracted into mountain-top islands where the birds have evolved their own local songs.

The isolation of different bird communities, shown in their songs, has also given rise to the fascinating question of whether the birds are gradually evolving away from one another, diverging into first, different races and ultimately perhaps, species.

Dr Wescott says studies of bird genetics in the area suggest that new races of birds may be beginning to emerge within particular species.

It has also raised the serious question of what will happen to the unique bird communities and their mountain-top rainforest environment if the global climate continues to warm and the cool upland area to shrink.