Numerous species have been driven extinct

Luiz Claudio Marigo The last known wild individual of Spix's Macaw disappeared in Brazil towards the end of 2000 Zoom In

Current extinction rates are exceptionally high. We are responsible for these extinctions, in the past mainly through the introduction of non-native species onto islands, and currently through increasingly extensive habitat destruction on continents. Without concerted action, current extinction rates will increase because there are time-lags before species finally disappear.

Species are going extinct at exceptional rates

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 are difficult to document, but birds are one of the best-known groups of organisms, and we have reasonably comprehensive information on recent avian extinction rates. More than 150 bird species are known to have gone extinct (or are very likely to have done so) in the last 500 years. Most historical extinctions were of species restricted to small islands. However, the rate of extinctions on continents appears to be increasing (see pdf case study, box 1).

We are the cause of these extinctions

Humans have been the cause of the vast majority of recent and historic extinctions. In the last two millennia, over 2,000 bird species on Polynesian islands may have been driven extinct as a result of human activities, often through the introduction of nonnative species of rats. The increasing wave of extinctions on continents is a direct result of large-scale habitat destruction and degradation, often combined with hunting. Information from Australia shows particularly clearly how species deteriorated in status until going extinct as a result of human impacts (box 2).

Current figures underestimate probable extinction rates

It takes some time for species finally to go extinct as a result of habitat loss and reductions in numbers (box 3). The persistence of tiny populations, doomed in the absence of intervention, means that effective extinction rates could be even higher than suggested by tallies of recent extinctions. Studies show that many species have already been extirpated from large parts of their ranges. In the worst-hit parts of the world, such as the Atlantic Forests of south-east Brazil, some species have lost over 99% of their original range (box 4). Considerable effort is now required to bring such species back from the brink of extinction and to reverse the deteriorating status of many more that are threatened. However, the moral case for doing so is overwhelming, because there are no second chances: extinction is forever.

Boxes: case studies and scientific analyses

Download SOWB pp.12–13 (PDF, 847 KB) containing the following:

1. We have lost over 150 bird species since 1500
Rate of extinctions on islands

2. In Australia, the worsening status and extinction of birds can be linked to human impacts
The percentage of 1,081 Australian bird taxa retrospectively assigned to each of the IUCN Red List categories, at 50 years from 1750 to 2000

3. There is a time lag before species go extinct
Correlation between numbers of threatened species and numbers of predicted extinctions based on habitat loss, South-east Asia. Relaxation index v. time since isolation for forest fragments.

4. Many species have already disappeared from large parts of their range
Density of GTBs extirpated from parts of their ranges across South and Central America and the Caribbean