Between a quarter and a third of the world's wildlife has been lost since 1970, according to data compiled by the Zoological Society of London.

Populations of land-based species fell by 25%, marine by 28% and freshwater by 29%, it says.

Humans are wiping out about 1% of all other species every year, and one of the "great extinction episodes" in the Earth's history is under way, it says.

Pollution, farming and urban expansion, over-fishing and hunting are blamed.

The Living Planet Index, compiled by the society in partnership with the wildlife group WWF, tracks the fortunes of more than 1,400 species of fish, amphibians, reptiles, birds and mammals, using scientific publications and online databases.

It said numbers had declined by 27% in the 35 years from 1970 to 2005.

Some of the worst hit are marine species which saw their numbers plummet by 28% in just 10 years, between 1995 and 2005.

Populations of ocean birds have fallen by 30% since the mid 1990s, while land-based populations have dropped by 25%.

Among the creatures most seriously affected have been African antelopes, swordfish and hammerhead sharks.