Research at the Queen Elizabeth National Park, Uganda, showed that 15% of female elephants and 9% of males in the park were born without tusks.

In 1930 the figure for both male and female elephants was only 1%.

Genetic accident

Elephants appear to be losing their tusks

Experts say the reason why some elephants are tuskless is a result of a chance genetic mutation.

They say elephants are losing their tusks as a rapid and effective evolutionary response to escape slaughter by ruthless and resourceful poachers who kill elephants for their ivory trophies.

The BBC's Science Correspondent, John Newell, says the continuing change shows how rapidly evolution can react in response to pressures that threaten the survival of a species.

This allows them to live, breed more freely and produce more offspring without tusks.

Growing trend

Evidence of a trend in tuskless elephants has been reported elsewhere.

Mark and Delia Owens recorded an unusual number of such elephants in 1997 while carrying out research in Zambia's North Luangwa National Park.

Published on the National Wildlife Federation's Website, they write: "Our research indicates that more than 38% of Luangwa elephants carry no tusks.

"Other researchers have reported that in natural, unstressed populations, only 2% of the animals are tuskless."

Crippled creatures

Tuskless elephants are paying a heavy price for survival.

Tusks are used to dig for food and water, to dig up trees and branches and move them around, for self defence and for sexual display.

Conservationists say an elephant without tusks is a crippled elephant.

They say that while being tuskless is better than being dead, they hope that less drastic ways can be found to protect elephants against poachers.