Click photo to enlarge
Ecologist Dr Murray Efford records bird songs in the garden
at his Wakari home. Photo by Peter McIntosh.
Dunedin ecologist Dr Murray Efford spent 20 years
devising a computer modelling system to accurately count one of
New Zealand's most ecologically damaging animals, the possum.
Now, with some lateral thinking and collaboration with
scientists in the United States and Scotland, he has been
able to adapt the system to count birds and says it could be
used to tally any land and sea creatures, including
endangered species.
The scientists' work, reported on Friday in the British
Ecological Society's Journal of Applied Ecology, is being
regarded as a major advance because it enables scientists to
monitor bird populations using an acoustic technique without
having to physically catch and release specimens.
Dr Efford, an adjunct senior lecturer in the University of
Otago's zoology department, said yesterday it had been fun
and satisfying working on the project.
"You beaver away in a corner, and if you can find something
which is generally useful it is an unexpected bonus."
The technique developed by Dr Efford and Deanna Dawson, of
the US Geological Survey, is a combination of recording bird
songs from multiple locations and applying a mathematical
formula to the information to calculate the number of birds
in a given area.
A sound spreading through a forest or other habitat left a
"footprint", Dr Efford said.
The size of the footprint depended on how quickly the sound
attenuated (weakened).
Mathematically, there was a unique combination of population
density and sound attenuation rate which best matched the
recorded sounds.
Computer methods were used to find the best match, and
thereby estimate population density, he said.
Statistician David Borchers, from St Andrews University in
Scotland, helped refine the computer modelling.
Dr Efford and Ms Dawson have been trialling the system for
about five years with the ovenbird, a warbler more often
heard than seen in the forests of Maryland in the United
States.
When compared with the standard method of netting birds to
count them, the new acoustic technique was found to give a
more accurate estimate of bird numbers, he said.
Potentially, the acoustic technique could be adapted for
hydrophones, underwater microphones used to measure
hard-to-reach populations of marine mammals such as whales
and dolphins, he said.
"Developing ways of estimating whale and dolphin numbers
acoustically is seen as critical for understanding these
species' populations."
Dr Efford said he hoped the technique could also be used to
gain a better understanding of New Zealand endangered bird
species, such as the mohua.
allison.rudd@odt.co.nz
