In modern times, birds have gone extinct at an exceptionally high rate, estimated to be 1,000 to 10,000 times the natural background rate. Most documented extinctions have been of species restricted to small islands, but the rate of extinctions on continents is increasing. Some species survive in very small numbers or with tiny ranges and are almost certainly doomed to extinction, unless effective conservation measures are urgently taken.
Extinction is permanent and irreversible. Although extinction is a natural process, current and projected extinction rates are estimated to be 1,000 to 10,000 times the natural background rate. Extinctions in general are difficult to document, but we have reasonably comprehensive information on recent extinction rates amongst birds. More than 150 bird species are known to have gone extinct (or are very likely to have done so) in the last 500 years. More than ten times as many may have gone from the islands of Polynesia in the last two millennia although information on these is much less complete. While most documented historical extinctions have been of species restricted to small islands, the rate of extinctions on continents appears to be increasing (). Information from Australia shows particularly clearly how species have deteriorated in status before going extinct as a result of human impacts ().
A species becomes formally extinct once the last surviving individual has died. Before that happens, species are often reduced to tiny populations that may persist for some time but are nevertheless almost certainly doomed to extinction in the absence of intervention (). Such extinction-prone species are chiefly found in areas where there has been extensive habitat loss, such as the Atlantic Forests of south-east Brazil, where some species have lost 99% of their original range (). Taking these species into account would increase current extinction rate estimates considerably.