Kiwi scientist makes a twitter breakthrough

Ovenbird song

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KIWI INGENUITY: Microphones inside plastic plant pots, muffled against wind noise, were used to record the ovenbird, below.

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Bird watchers have long waxed lyrical about the benefits of listening to birds, but now a recording of their tweets has led a Kiwi ecologist to a scientific breakthrough.

Murray Efford, of Otago University, and American ecologist Deanna Dawson have developed a world-first technique that enables scientists to measure how many birds are in an area by recording them, instead of simply counting them.

Dr Efford said the discovery could be used in the future to help measure dolphins, whales, and other animals that lived in areas which made them difficult to count.

Though the study recorded the warbles of the American ovenbird, a small thrush-like bird, Dr Efford said the technique would now be used to measure numbers of New Zealand's only surviving native owl, the morepork.

Morepork, or ruru, are found in mainland forest and on offshore islands and as they could sometimes be heard calling each other at night, Dr Efford said it would be useful to use those sounds to find out more about their numbers.

The researchers developed the technique by recording 375 minutes worth of birdsong in June, at an American deciduous forest at the Patuxent Research Refuge in Maryland.

By setting up four microphones, each bought for about $12 each, they recorded the song of an ovenbird, which Dr Efford said was more often heard than seen.

He said a certain amount of Kiwi ingenuity was used to set up the microphones, which were "housed" in plastic plant pots and covered with fluff to reduce wind noise.

The combined recordings were fed through a computer program the researchers developed to work out how many birds were in the area.

They already had a good idea of the population of the ovenbird in the area, as it had been the focus of studies for the past five years.

The "acoustic technique" would enable researchers to count birds more accurately than traditional methods, which Dr Efford said used nets and could be stressful for birds.

Scientists overseas were working on developing underwater microphones, and once these were ready, the technique could be used to count marine animals, which would be critical for understanding whale and dolphin populations.

Recording

The ovenbird researchers set up four omni-directional microphones which record sound coming from all directions within a 21 square metre area. Over five days, they moved the microphones to 75 localities, where they took five-minute recordings. By combining the recordings from all four microphones, the ecologists came up with a single recording that was fed into a computer program. That program generates a spectogram, which is a graph of the sounds. Each bird has a slightly different sound, which is shown in the graph. Researchers can interpret the graph to count how many birds there are in an area.

- © Fairfax NZ News