"There are many more millions out there which could be under serious threat."
Water resources strained
Scientists also examined 3,120 freshwater fish species and found that 1,147, or a third, are facing extinction due to a strain on global water resources caused by pollution and intensive usage.
"Creatures living in freshwater have long been neglected," Jean-Christophe Vie, the deputy head of the species programme at the IUCN, said.
"This year we have again added a large number of them to the IUCN Red List and are confirming the high levels of threat to many freshwater animals and plants.
"This reflects the state of our previous water resources. There is now an urgency to pursue our effort but more importantly, to start using this information to move towards a wise use of water resources."
The endangered list also includes 1,360 species of dragonflies and damselflies, which scientists say are at risk of disappearing.
Some species have recovered following conservation efforts, the IUCN said.
But for others, conservation efforts are likely to come too late.
The Kihansi spray toad of southern Tanzania is now believed to be extinct in the wild due in part to a fungal disease that has affected the species, and the drying up of a dam in the gorge where it lived.
Last year, the Red List examined 44,838 species and found that a similar proportion - 16,298 species - were close to becoming extinct.
"What we haven't got this year is good news," Vie said.
The IUCN says the actual situation may be even worse than reflected, because researchers have been unable to find data for 14 per cent of the species surveyed.
In addition, the survey only covered a fraction of the world's species.