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In pursuit of our mission to promote conservation, facilitate rediscovery, and preserve a record of extinct species, it is important to have clearly defined and ranked categories of concern. Although we acknowledge that the study of the current mass extinction event is a developing field, and concepts will evolve, below we provide working definitions for the three core categories of imperiled, lost, and extinct, which authors should use when writing Reports (see Author Guidelines). The three categories are ranked in order of the weight of evidence that a species is at risk of extinction (Imperiled, Lost) or putatively already extinct (Extinct).
Note that the definitions below refer to species, but equally apply to subspecies, varieties and other taxonomic units, and may be used for undescribed species with sufficient documentation (see Author Guidelines).
1) Imperiled species are those taxa for which there is some reasonable cause for concern, and this might be apparent in ways that include, for example, extirpations (loss of local populations), range contractions, increasing rarity throughout its range, over-harvesting, or loss of key resources for particular life history stages (e.g., through habitat destruction on overwintering grounds or, for parasitic organisms, through declines in host species). Imperiled is the most flexible category and can be used to motivate conservation, additional search efforts to locate the species, and other actions.
2) Lost species are those that have not been reported in the wild for at least ten years*. The designation of lost after ten years without documentation is not inherently dependent on the amount of search effort, but of course a species that has not been seen in ten years of intense search effort will be of greater concern than a species that has been the focus of only minimal search effort or monitoring. Thus the designation of lost comes with implicit gradations of concern, and should be reported in that spirit (see Author Guidelines).
* Long, B. and Rodríguez, J.P., 2022. Lost but not forgotten: a new nomenclature to support a call to rediscover and conserve lost species. Oryx, 56(4), pp.481-482.
3) Extinct species are either those that are already formally confirmed to be extinct, for which we can say with considerable confidence that they will never be seen again, in the wild or in captivity, or species that have likely gone extinct, in which case they are proposed to be extinct in the article (see Author guidelines). In the words of the International Union for Conservation of Nature, a species is extinct if there is no reasonable doubt that the last individual has died, which should be verified with extensive search effort by experts. In most cases, many decades will be needed to be confident that a species is not just lost, but extinct, although a more rapid timeline is possible in cases of, for example, range-wide habitat destruction.
The Jackson’s Climbing Salamander, also known as the 'golden wonder,' was rediscovered in 2017 after being lost to science for more than 40 years. A park guard at Guatemala’s Yal Unin Yul Witz Reserve spotted the salamander during a lunch break, just a few years after Re:wild helped establish the reserve to protect other salamander species in the area. (Photo: Re:wild)
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