Estimating Bird Population Size Using Bird Song – BES Research

Ovenbird -Copyright Murray EffordNew research published online today in the British Ecological Society’s Journal of Applied Ecology offers a way to more accurately estimate the size of bird populations using bird song. The technique could offer a way to assess the numbers of hard-to-spot species of bird and could even be used to track the population density of whale and dolphin species.

Deanna Dawson, US Geological Survey, and Murray Efford, University of Otago, New Zealand, recorded the sounds of the Ovenbird, a species of both which is both hard to see and which has a distinctive call, in the Patuxent Research Refuge, near Laurel, Maryland, USA. Using a ‘microphone array’ technique, placing four microphones at intervals and in different locations around the forest, the researchers were able to record the sounds of the ovenbirds and then to combine the recordings from each microphone. Using computer models, the researchers then conducted an analysis, based on the attenuation of the sounds and the relationship between this attenuation and population density, to find the ‘best match’ to the data. In this way they were able to accurately estimate the population size of the ovenbirds.

Biologists have long counted bird songs or calls to generate an index of bird abundance but this relies on being able to see the bird – to assess whether it is within a set distance from the observer. Existing methods of assessing population size also often depend on capturing the birds in nets, which can be very stressful for the animals. This is the first time that sound recordings from a microphone array have been translated into an accurate estimate of bird species populations.

The research has already generated interest from the press in the UK this morning, featuring as a lengthy item on the BBC Radio 4 Today Programme (approx: 7.45am GMT) .
Listen Again to the Today Programme on BBC I-Player

See the Press Release on the BES website: Ecologists sound out new solution for monitoring cryptic species

Deanna K. Dawson and Murray G. Efford (2009). Bird population density estimated from acoustic signals, Journal of Applied Ecology, doi: 10.1111/j.1365-2664.2009.01731.x, is published online today.