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%.
Another, the baiji - or Yangtze River Dolphin - may have been lost altogether.
It said that while species' decline does appear to have flattened off in recent years, it is "very unlikely" that the 2010 target will be reached.
The WWF said that over the next 30 years, climate change was also expected to become a significant threat to species.
Colin Butfield, head of campaigns at WWF UK, said: "Biodiversity underpins the health of the planet and has a direct impact on all our lives, so it is alarming that despite an increased awareness of environmental issues we continue to see a downward trend."
The charity also warned that a failure to stop biodiversity loss would have a direct impact on humans.
Director general James Leape said: "Reduced biodiversity means millions of people face a future where food supplies are more vulnerable to pests and disease and where water is in irregular or short supply.
"No-one can escape the impact of biodiversity loss because reduced global diversity translates quite clearly into fewer new medicines, greater vulnerability to natural disasters and greater effects from global warming."
The WWF is calling on governments meeting in Bonn to honour their commitments to put in place effective protected areas for wildlife and to adopt a target to achieve net annual zero deforestation by 2020.
The UK's Biodiversity Minister, Joan Ruddock, said the report showed that the international community had to work together to stem the decline.
"The fact that human activities have caused more rapid changes in biodiversity in the last 50 years than at any other time in human history should concern us all," she said.
"Supporting wildlife is critical to all our futures and the UK will continue to give strong support to international action.
"Schemes such as the Darwin Initiative have used UK expertise to help more that 490 wildlife conservation, regeneration and research projects in 146 countries."
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