Bird Song Intensity Used To Calculate Size Of Population


Scientists have for the first time worked out a way of using birdsong to accurately measure the size of bird populations. The sound recordings from a microphone placed in forests or woods can now be translated into accurate estimates of bird species’ populations and could revolutionise this branch of ecology.

Because the new technique is so accurate it could lead to a major advance in our ability to monitor whale and dolphin numbers as well.Measuring populations of animals such as birds, dolphins and whales has always been difficult because they are often heard but not seen.Actually trying to count numbers is extremely time consuming.

Biologists have long counted songs to get an idea of bird abundance but it is much harder to work out the actual density.Existing methods need observers to measure either the distance to each bird, or whether they are within a set distance from the observer.Now Deanna Dawson of the US Geological Survey and Murray Efford of the University of Otago, New Zealand, have developed a system that combines audio equipment with computers.

The system works by placing four microphones close to the ground in a square with 80ft sides.The recorded birdsong is then analysed using a mathematical model on a computer that can detect the “attenuation” or varying intensities of the sound – which is an indication of how close the bird is to the microphones.By crunching all the information together, the computer can work out the sound “footprint” which indicates the density of birds.“We devised a way to estimate population density of birds or other animals that vocalise by combining sound information from several microphones,” said Miss Dawson.

“A sound spreading through a forest or other habitat leaves a ‘footprint’. The size of the footprint depends on how quickly the sound attenuates.”

The new technique might be applied to measuring hard-to-reach populations of marine mammals, such as whales and dolphins.Developing ways of estimating whale and dolphin numbers acoustically is seen as critical for understanding these species’ populations.The findings were published in the journal of Applied Ecology.



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