Scientists have for the first time worked out a way of using birdsong to accurately measure the size of bird populations.  

Biologists have long counted songs to get an idea of bird abundance but it is much harder to work out the actual density.
The sound recordings from a microphone placed in forests or woods can now be translated into accurate estimates of bird species' populations and could revolutionize 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.
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 U.S. 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 analyzed 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 vocalize 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.”
Developing ways of estimating whale and dolphin numbers acoustically is seen as critical for understanding these species' populations.
(Source: Telegraph)