- Written by Nadia O'Carroll
Birds generate sound through a vocal organ called a syrinx which is located at the junction of 2 bronchi (air passages). When air from the lungs is passed over the membranes a sound is produced, the membranes over each bronchi can operate together or independently, which in effect gives birds two voices. Muscle pairs control the syrinx; birds may have between 1 and 9 muscle pairs depending on the species. By adjusting the force of air, the vocal tract and the shape and tension of the membranes birds are able to create an amazing range of sounds.
Birds make brief, simple vocalisations described as calls eg alarm calls and these are instinctive. Birds also make much more complex variable vocalisations described as songs, and these are partly inherited and partly learned. Baby birds babble, practice songs and imitate their parents in much the same way as children learn to speak. An example of this behaviour is evidenced by a group of Superb Lyrebirds. In 1934 a number of Superb Lyrebirds were re-located from Victoria to Tasmania, 30 years later the Tasmanian Lyrebirds still imitated the songs of Victorian birds in their mimicry repertoire.
Some bird species only learn songs in the first year of life, but other species continue to learn new songs throughout their adult life. Birds reared in isolation from other birds only have a limited song, which is fixed for life even if they are exposed to other birds. Some species only have one song, some have hundreds – the Brown Thrasher has 3000. Within a species there are also variations in songs, these are called dialects. Birds also sing differently according to the weather, season, location, activity, age and ambient noise. When habitat and the massed bird chorus are depleted, it also seems to have an effect of reducing the variety of birdsong.
TMNHA Bird Group has produced a CD-ROM from its own photographs and recordings; this is a very good resource for anyone interested in identifying the songs and calls of our local birds. The CD costs $20 and is available from the Visitors Information Centre.
People may also like to participate in a study of birds in backyard birdbaths, which is being conducted by Darryl Jones of Griffith University. Forms can be downloaded from the Internet at www.wildlife.net.au. If you do not have the Internet TMNHA will provide forms (please call 5545 3551). If you don’t have a birdbath why not install one in your garden and help our thirsty feathered friends.