Elephant age can be estimated from voice

Researchers have found that the age of an elephant can be estimated based on its vocal sounds.

It could be a powerful tool for conservation, and one that's less invasive and more cost effective than other methods, such as radiotagging, researchers said.

Researchers said that vocal sounds helped them distinguish infants, calves, juveniles, and adults with 70 per cent accuracy and youngsters (infants/calves) from adults with 95 per cent accuracy.

The call feature that was most useful for doing this was overall frequency - not surprisingly, since vocal frequency usually decreases as an animal grows larger, researchers said.

The need to control and monitor elephant populations is evident because poaching, human disturbances, habitat loss and the resulting human-elephant conflict pose serious threats to elephant populations worldwide, researchers said in the study published in the journal Bioacoustics.

Acoustic recordings are an efficient way (apart from cost-intensive and invasive GPS and satellite tracking) to sample populations and obtain reliable estimates of species occurrence and potential abundance.

Elephants produce powerful sounds with frequencies in the infrasonic range, called 'rumbles'. They are largely below the range of human hearing yet can travel distances of up to several kilometres.

Elephants are suited for acoustic monitoring even in dense forests. It has been known that these sounds could be used to count elephants remotely but not determine the age.

"That elephants produce these incredibly low frequency sounds which travel across many kilometres is amazing enough. But what's even more amazing is that these sounds can be used to assess not just the number, but the ages, of elephants over large distances. That's a powerful tool for conservation, and one that's less invasive and more cost effective than other methods, such as radiotagging," said Andrew Horn, American Editor of Bioacoustics, Dalhousie University, Canada.

The researchers statistically analysed the frequency patterns of calls given by different individuals. Identifying which individual is calling in a group of elephants is extremely hard, but they managed by watching the elephants carefully, noting when they opened their mouths or gave other signs of calling.

Conservationists might now be able to monitor not only the number, but also the demographics, of elephant groups over large distances, researchers said.