Washington, Nov 27 (IANS) Ecologists have worked out a way of using bird song recordings to measure the size of bird populations.
This is the first time sound recordings from a microphone array have been translated into accurate estimates of bird species’ populations.

Birds communicate by singing or calling and biologists have long counted these cues to get an index of bird abundance.

But it is much harder to work out the actual density of a bird population because existing methods need observers to measure either the distance to each bird, or whether they are within a set distance from the observer.

Developed by Deanna Dawson of the US Geological Survey and Murray Efford of the University of Otago, New Zealand, the technique is an innovative combination of sound recording with spatially explicit capture-recapture (SECR).

“We devised a way to estimate population density of birds or other animals that vocalise by combining sound information from several microphones. A sound spreading through a forest or other habitat leaves a ‘footprint’,” says Dawson.

Dawson and Efford developed the method by recording the ovenbird - a warbler more often heard than seen - in deciduous forest at the Patuxent Research Refuge near Laurel in Maryland, US.

The new acoustic technique gives a more accurate estimate of bird numbers than using nets to capture birds, which can be stressful for the birds as well as time consuming for the researchers, says an Otago release.

These findings were reported in the British Ecological Society’s Journal of Applied Ecology.