The Great Auk was a 2-ft.( 75-cm ), flightless North Atlantic seabird, related to puffins and penguins. Large breeding colonies of the great auk once gathered on rocky islands and coasts of the North Atlantic in Canada, Greenland, Iceland, the British Isles and Scandinavia.
Hunters killed so many Great Auks for food and feathers, that when the last one was slaughtered in Iceland on 4 June 1844, the species became extinct.
The little auk, which nests in Greenland and Iceland, is not extinct.
Too many unique and irreplaceable plants, animals, insects, birds, and fish have already gone extinct - not as part of a natural process but rather because of the hand of man. It is estimated that human activities threaten 99% of all birds, mammals and amphibians on the danger list of species under threat of being extinct.
The biggest threat by humans is the the loss of habitats, which affects more than 80% on the danger list.
Climate change is also increasingly recognised as a serious threat
Other issues relating to human activity include introduction of alien species, over-exploitation and pollution
The polar bear, hippopotamus and many shark are listed as species threatened with extinction by the world's bio diversity agency.
It is estimated by the World Conservation Union (IUCN) that there are more than 16,000 at-risk species.
Polar bears are affected by loss of Arctic ice, which the IUCN attributes to climatic change. Polar bears need ice floes in order to hunt seals and other prey; without it, their food supply will decline.