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Last Updated: Saturday, 18 June, 2005, 09:55 GMT 10:55 UK
Seismic sensors count elephants
By Fiona Proffitt

Elephants, Stanford
Geophones could help monitor elephant numbers and distribution (Image: Mark Shwartz)
American scientists have come up with a hi-tech method of surveying elephants, using military-designed seismic sensors to detect their footsteps.

Researchers from the Geophysics Department at Stanford University used the sensors to monitor African elephants and other large mammals in Etosha National Park, Namibia.

The "geophones" - originally designed by the US military to detect enemy troop movements in the Vietnam War - were deployed to pick up vibrations caused by animals walking to a waterhole.

The researchers then analysed digital recordings of the footsteps to separate out the unique sound signatures of different species.

Walking vibrations

The results, reported in the Journal of Applied Ecology, show that the technique worked well at distinguishing elephants from other animals (giraffes, lions, gemsbok and humans), with an average success rate of 82%.

Geophones, Jason Wood
The geophone was originally designed by the US military (Image: Jason Wood)
But it was not so good at counting elephants: the sound energy created by the elephants' footsteps only gave a 55% accurate picture of the number of animals visiting a waterhole, observed from a nearby tower.

The accuracy could be improved with an array of geophones, an idea the team is currently testing, said geophysicist Jason Wood, who led the research.

The Stanford group believes the technique has potential as an alternative to aerial surveys and labour-intensive dung ball counts, currently used to census elephants for conservation and reserve management purposes.

In particular, geophones could be used to improve estimates of elephants in densely forested areas of Central Africa, where aerial surveys are useless.

"Conservation management would be improved by more accurate methods for monitoring and estimating the size of elephant populations or other large mammals in Central Africa, as these populations are relatively small and threatened by poaching," the team said.

Practical constraints

Geophones could also be used to monitor elephants' use of certain sites over longer time periods than current methods, added Dr Wood.

Laying the geophones,  Jason Wood
Some commentators are sceptical of the technique's usefulness (Image: Jason Wood)
But some elephant ecologists are sceptical of the technique's usefulness, given the problems in detecting elephant numbers accurately and practical constraints, such as needing to change batteries frequently.

"Given the detection radius is only 100m, you would need literally hundreds of them just to cover a few square kilometres," said Matt Walpole, of Fauna and Flora International, in Cambridge, UK.

"Monitoring elephants in the whole of the Congo Basin using this method would clearly be impractical and cost prohibitive."

And Dr Bob Smith, a researcher at the Durrell Institute for Conservation and Ecology, in Canterbury, UK, added: "These hi-tech approaches are often suggested, but getting them to work in places like Central and West Africa is very difficult."

Low-tech approaches are generally more sustainable, and the money saved could be spent on properly equipping the people charged with protecting the elephants from poachers, he said.

Geophones are not yet "a realistic alternative to conventional foot patrols and transects for monitoring elephant numbers and distribution over a wide scale," said Dr Walpole. But, he added: "It's an interesting and novel concept which is definitely worth exploring."

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