In the seas, entanglement in fishing nets emerges as the biggest factor, affecting 79% of marine mammals.
The 2008 list was for the first time that every known amphibian, mammal, and bird was assessed. But they only make up a tiny fraction of the world's wildlife.
Even if other plants and animals covered by the Red List are included, it means conservation decisions are made based on less than 4 per cent of the Earth's biodiversity.
What about the un-cuddly creatures?
"The status of the rest of the world's biodiversity is very poorly known".
"The problem is the size of some of these groups -- how do you assess a million plus beetles?"
One idea is to use something similar to a stock market index such as the Dow Jones.
"The disadvantage is you can't look at all individual species, but to address the bigger problems we have to understand things at an ecosystem, or habitat, level."
How many animals do we need to save to avert extinction?
Numbers aren't enough on the ERV blog explores this question.
Nicolas Entrup also discussed the numbers game for whales and dolphins on the BBC Green Room.
Is it worth trying to do something about this?
According to the report, 5 percent of threatened species have seen rebounds due to conservation efforts.
Why should we bother? Does it matter to humans if lifeforms go extinct?
For the first time, this year the United Nations Millennium Development Goals is monitoring biodiversity loss using the IUCN Red List Index.
"Species are harvested for food, medicines and fibres. They’re domesticated for agriculture and play an essential role in regulating local and global environments".
- Summary of key findings of the Red List report media reports
- from the IUCN website: Press release; Red List segment of the IUCN website has high resolution photos and case studies on species and a 2 minute video B roll prepared by Arkive (www.arkive.org); IUCN Red List of threatened species