Comment 1: 50 year rule is generally acceptable for amphibians. Many are cryptic in their habit.

Comment 2: 50 year rule is generally acceptable for animals. Plants, with seeds that can stay dormant for long periods of time, are a problem.

Comment 3: 50 years is adequate for an organism that has taken several years to reach sexual maturity. But if a species reaches sexual maturity within one year, 50 generations is too long. Maybe we need a new category of "assumed extinct."

Comment 4: 50 years is practical -- but one problem is that in many biodiversity-rich developing countries no recent surveys have been made. Many species that are known from old names/specimens have not been surveyed in over 50 years and so could be declared extinct based on this lack of information (this indicates that even a 50 year rule does not solve the problem of dealing with species from inaccessible and unsurveyed areas; thus, the 50 year rule probably should not be used alone for resolving an extinction; surveying evidence is also required).

Birds Advisory Panel

Comment 1: 50 year rule is acceptable by weight of convention and utility - but one should recognize that the 50 year rule is not proof of extinction. (The rule should be implemeted with other criteria, as discussed in Harrison & Stiassny's (1999) fish paper).

Comment 2: 50 year rule is problematic. IUCN requires published evidence of sampling across space and time that is equivalent to the species life-history. Waiting 50 years may be redundant in some circumstances - the term "Provisionally extinct" or Apparently Extinct" could be applied in such circumstances. In other cases there may be habitats that are too inaccessible to sample and so a species could meet the 50 year rule simply through lack of sampling - "to have a criterion which is so unsophisticated that taxa endemic to unvisited places get listed as extinct would not be helpful. So this needs work.

Comment 3: 50 years was just sufficient for the takahe [1898-1948]. There must be a cut-off date and 50 years is as good as any. There will always be exceptions to whatever date is applied. For some groups, 100 years will not allow enough time for certainty, eg. McGillinay’s (?) petrel and the Chatham island taiko.

Comment 4: the 50 year rule is a reasonable one generally, but clearly it will prove too short for some cryptic and/or potentially widespread species." (So if it is to be used it must be applied in conjunction with other criteria).

Comment 1: the 50 year rule is a conservative approach. As for species that may be rare or difficult to sample, this is an issue that persistently affects listing decisions in the US. Where there is reason to suspect that a particular organism may simply be difficult to collect (eg. , moths not attracted to black light traps) the 50 year rule should probably be suspended pending at least some attempt to locate an extant population according to whatever methods are available. These issues are best addressed by recourse to experts familiar with the biology of the organisms in question.

Comment 2: a 50 year rule has been used in a case of a putative extinction of a Hawaiian carabid beetle. A 100 year rule will of course give more confidence of loss than a 50 year rule (just as one would find by using different p-values for estimating statistical significance. If nobody has looked for the species in 100 years then that should also be revealed; ie. sampling should be rigorous.

Comment 3: the rationale for the 50 year rule seems a good one, in general principles.

Comment 3: this is OK for plants or vertebrates, and also probably OK for some lepidoptera. We might need to be more flexible for beetles.

Comment 1: there are cases where the 50 year rule seems unnecessary to justify an obvious extinction, such as extinctions in cities where habitats are totally destroyed; whereas in other cases such as the Amazon the extinction is much less definitive and so the 50 year rule may be more helpful. However, the 50 year rule can be helpful in justifying the extinction, but it should have some correlation to the species' life span. Also, it happens to be related with the latest activities after the World War 2.

Comment 2: 50-year rule may be OK for deep sea fishes or species inhabiting large rivers, or forest insects etc. But in the case of species restricted to a single spring in a desert (e.g. Mexican pupfishes), if the spring dries out for a few years then it seems that the case should be declared resolved much faster. Waiting for 50 years in such obvious cases is counter-productive because it creates the possibility that people will talk about obvious extinctions when CREO still do not list them as resolved. So it creates a lack of trust in who to believe; this is a serious problem when we want to use known cases as examples of what will happen in areas to be impacted by new projects. Although there is a need for some suitable waiting period before declaring a species extinct, it may not be sensible to call a species 'probably-extinct' for 50 years: such semantic subtleties can be used as an argument for not doing anything. Perhaps the definition of the requisite waiting period should allow for different periods for different categories, habitats, habits, areas (although this is against the justified, advocated aim of having criteria applicable across taxa). The wording of a rule for a suitable waiting period should be correctly selected, not only to reflect the truth, but also to prevent misuse or semantic distortion.

Comment 3: 50 year rule seems logical. For example, if the Comoros islands population of the coelacanth had become extirpated a few years ago, it might have seemed logical to assume the species was extinct if no 50 year rule was applied; but recent discovery of the Indonesian population would have shown this to be wrong. This example also underscores some significant problems in evaluating species from a vast environment like the ocean. (The marine example shows a very real reason for a 50 year rule, to give an opportunity to find a species in an extensive environment; but it also shows that just because the 50 year rule is met the species is not necessarily extinct, because the environment might be too large to cover in 50 years. Panelists for mammals have also addressed this problem, stating that sampling and decisions of extinction should be weighted according to the size of their environment; this is very sensible in theory, but it may be more difficult to apply practically?).

Comment 1: while there are valid reasons for adopting the 50 year rule, in practice there is little functional relevance to this rule for lepidoptera. Because of rapid generation times, and high variability in abundance and apparency of many Lepidoptera in successsive seasons, such hard and fast lines are unwise. Extinctions may be detected much more rapidly, and it would be better to have greater flexibility here for such shortlived animals.

(Another entomologist has warned against use of 50 year type rules when sampling is not evident; insects can show enormous changes in population numbers so may be apparently absent for some decades before re-appearing).

Comment 1: 50 year rule is useful for species that are easily detected, but not good for species that are easily overlooked or are in habitats that are difficult to sample. In these cases it must be associated with other criteria to test for evidence of presence or absence of the species. (Fish Panelists stated exactly the opposite - the 50 year rule seems unecessary where the species can easily be located, because there is no reason to assume that it might be present but not detected. However, the comment made here is valid: when species are typically difficult to locate then one should not assume that, just because they have not been seen for 50 years, they are therefore extinct. The 50 year rule must be backed up by indication of sampling etc. in these circumstances).

Comment 2: 50 year rule is not acceptable; several Australian mammal extinctions are undisputed but have occurred within the last 50 years.

Comment 3: 50 year rule is very problematic. The species might not be directly studied because no money is available (however, in these circumstances, the 50 year rule may provide a safety net for an otherwise overlooked species, ie. it is seen by chance despite a lack of intense sampling. If the species is not seen, then the rule must be applied in conjunction with some indication of level of sampling, to reduce the chance of incorrectly listing the species as extinct, as noted above). But the rule may also preclude the inclusion of a species that is probably extinct. Perhaps the time can be reduced.

Comment 4: supports the 50 year rule.

Comment 1: This may be OK in the case of widely distributed taxa. There are many highly localized taxa where verification of extinction can be achieved readily. Rules should be flexible enough to take this into account. If a specialist panel for the group in question thought that the 50 year rule was necessary to apply in a particular case, then the rule should be accepted in this case. However, many mollusk species would not have been collected over a fifty year period simply because no one has done it.

Comment 1: this is significant problem because reptiles and species not seen or collected for over 100 years are "rediscovered" with some regularity. The 50 year rule should be retained in cases of species occurring in areas/habitats that have adequate sampling or at least reasonably frequent visits by specialists. A 100 year rule might be more appropriate for remote or inaccessible areas. Alternatively, 25 years may be acceptable in cases in which all appropriate habitat has been destroyed or the distribution is known to have been very restricted.

Comment 2: some form of annotation on the list that a species has not been searched for in appropriate habitats/within the known range of the species; or XX man-hours/weeks/months spent in species-directed searches etc. (Some quantification of effort of sampling would be very informative; I think it will be difficult to develop a quantitative measure that can be consistently and accurately to fieldwork for diverse taxa. However, even simply noting the number of times fieldwork has been reporting for a particular area might help. This should be covered in the additional criteria discussed below).

Comment 3: 50 year rule is acceptable

Comment 4: the 50-year rule is good enough to estimate extinctions if the species corresponds to the possibilities (1), (2), and (3) above. A 50 year period is reasonable for most species of reptiles, even cryptic species.

Comment 5: the 50 year rule seems reasonable, especially given that this rule does not preclude listing species that are most likely extinct - it merely puts them in a different category to indicate that the species has met other criteria except for the 50-year rule. For example some species that have a very limited distribution can with some degree of accuracy be listed as extinct if not recorded/collected under the 50 year rule. The best option would be to allow exceptions to the 50 year rule, using your examples 1-3 above.