In New Zealand one of our radio stations broadcasts native birdsong each morning. It is obvious that seabirds have a much harsher screeching sound than the more melodious bush and land-based birds. In fact, I can usually tell a bird鈥檚 habitat simply by the sound it makes. Why is there such a difference, and is it the same throughout the world?
鈥� Birdsong indeed varies by habitat type because the habitat has a profound effect on how these long-distance signals are transmitted. To minimise habitat-induced degradation, the acoustic adaptation hypothesis predicts that birds living in dense forests will have slower and more tonal calls, while those living in more open habitats will have faster-paced and buzzier calls.
The effect is most pronounced when comparing contrasting habitat types, such as very open and very closed ones. Other factors, including the songs of species competing for acoustic space and the songs produced by closely related species, can also play a role.
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Daniel T. Blumstein, Department of Ecology and Evolutionary Biology, University of California, Los Angeles, US
鈥� The subject is more complex than the question suggests. The South African bush hosts croaking corvids, harmonising antiphonal shrikes, shrieking parrots, raucous francolin, swizzling weavers and tweeting wagtails.
Calls seem to be adapted to distance, noise, obstacles, habit and competition. The most elaborate singers inhabit open bush, where their song can convey complex information over long distances. In thick bush, only deep ventriloqual notes such as those of the ground hornbill carry for any distance. White-eyes foraging among dense leaves cheep softly, keeping flocks together at short range.
鈥淭he most elaborate singers inhabit open bush, where their song can convey complex information鈥�
Even the apparently unsophisticated croaks, screams and yarps of seabirds vary in complexity and carrying power according to their habits and individual circumstances. When calling through wave noise over long distances they tend to screech shrilly, whereas when they are intimate they are quieter.
Details vary, but the fundamental principles of auditory information encoding and transfer seem inescapable.
Jon Richfield, Somerset West, South Africa