Many have been hunted or killed on sight for centuries, while others like bats and the hazel dormouse have been deprived of their habitats by people building on natural lands.
Man-made pollution is also an issue for mammals, along with the introduction of non-native species.
There are some reasons for hope, though, not least for wolves and bears.
Wolves were wiped out from the UK by the end of the 17th century because of deforestation and murderous royal decrees, while bears dwindled in number during the medieval times.
Regional reintroductions of beavers and pine martens have also worked well, but humans must still change their behaviour to help these at-risk species to flourish - otherwise they'll soon be gone forever.
