Rediscovery versus Relocation of "Missing" Taxa

By Branden Holmes

A list of rediscovered species and subspecies seems at first easy to compile, apart from the obvious difficulty of getting hold of all of the relevant literature. However, the distinction between extinction and a lack of sightings quickly blurs once one starts to research. Just because a taxon has not been seen in many years does not necessarily mean that it is likely to have become extinct. Many species live in remote areas away from human habitation, and as scientists rarely travel to these localities records of these plants and animals will obviously be similarly rare. Whereas for a species which either mainly or wholly inhabits an area which corresponds with a high human population a complete lack of sightings should be regarded as far more reflective of the actual conservation status of that species. Most species occupy a natural range somewhere intermediate between these two extremes of socio-geography, and hence the probability of their persistence or extinction after x number of years without a definite sighting is difficult to quantify, making it difficult to set conservation targets and priorities. In this particular case, deciding which "missing" taxa to search for.

Conservation Biology

Conservation biology has two main goals: to preserve biodiversity, and to preserve genetic diversity. Normally these go hand in hand, however there are sometimes difficult decisions which require biologists to concentrate on one to the detriment of the other. It is not always possible to conserve a viable population of genetically healthy individuals. Sometimes we need to conserve the species without as much regard to genetic diversity as is preferable under ideal circumstances, and can then go about making sure it persists long enough into the future that genetic mutations build up again to pre-bottleneck levels to restore genetic diversity (which often produces a very different genome, with polymorphisms at different chromosomal loci). But before biologists can go about conserving a species they first need to confirm that it still survives.

Many people would be surprised to learn that a great percentage of described species are known only from the type specimen or type series, in some cases collected more than 100 years ago. This is especially so for invertebrates. Scientists are constantly battling for funding, and that includes those who are not in the field of the life sciences. It would be nice to confirm the persistence of all of these taxa, however limited resources often puts a stop to any such hope. If a species does not face any obvious threats to its survival then any expedition just to confirm its persistence would be viewed as a waste of money. But there are other species whose continued existence is much less certain, and does potentially qualify for funding. But there are simply too many "missing" species in need of relocation/rediscovery to go and look for them all. Conservationists need to prioritise.

It is therefore of significant use to conservationists (and others) if we can create criteria which can be used to quantify what might be termed the likelihood of persistence (hereafter LP) of a taxon, which, if they are found again, would qualify as either rediscovered or relocated, depending upon whether their LP was <50% or not. With limited funds, conservations want the greatest "bang for their buck" so to speak, and hence it is necessary to weigh up the two factors of likelihood of persistence versus likelihood of extinction, which are really expressed in the same fraction (a 40% chance of survival means a 60% chance of extinction, and vice versa). Populations which have not been recorded in decades, but which face no obvious threats to their survival, justifiably deserve less conservation attention than a species which has been recorded many times before but whose population has dwindled in recent years to the point where it has not been recently seen, especially if species-specific searches have been conducted.

But expeditions/surveys often fail to find target species for any number of reasons, including: incorrect survey methods, insufficient area covered, insufficient planning, external factors such as the weather, etc. They are not fool proof, and usually several expeditions/surveys are needed to identify potentially extinct taxa, as each generally covers a different geographical area unless a taxon happens to be historically only known from a small area, perhaps the type locality only. But as rediscoveries as of recent show, we cannot write off species just because they have disappeared from their type locality, even if that is the only locality from which they are definitely known (ie. to which historical records were confined), because although the species may not have been recorded from other suitable habitat it is not always easy to distinguish phantom taxa (i.e. existing unseen in a given area) from ecological rarity (i.e. naturally rare).


But what about sightings of putatively missing or extinct species by natives? What if they continue to report it's existence although Western scientists never sight it, and it is subsequently found to still persist? Could that count as having been “rediscovered”? Simplistically, the only reasonable answer would be "no" as there is no good reason to view ethnoknowledge of a species as either inferior when compared with Western knowledge of plants and animals, or worthless, which is tantamount to racism. However, one needs to know whether those same native people could have some ulterior motive for "sighting" a plant or animal regularly. And hence it is important to weight their sightings according to their trustworthiness, which should be quantified as objectively as possible.

Native people are often an excellent source of knowledge about the flora and fauna which occur in a particular area, as well as which ones to avoid (e.g. which plants are edible and which are not), and which are harmless or, even better, of some economic use. It is not too much of a stretch to say that their lives depend upon it, especially when any potential help is days away if they are stung or bitten or attacked. But at the same time they may not be so non-chalant about sharing their knowledge, especially if that could potentially mean competition for a limited resource. So it is important to be aware of any possible deliberate misinformation being fed to the conservationist.


Until the early 20th century the collecting of museum specimens for collections went largely unabated. Any unusual specimen was simply shot, trapped, traded, or otherwise obtained in the hopes that it would prove to be a new species. It is not surprising then that museums are stuffed with unusual specimens; aberants and mutants whose true affinities may deceive. And until the discovery of the chemical structure of DNA (deoxy-ribo-nucleic acid), which allows scientists to delve into the genome of an individual and sequence its genes, they couldn't tell whether one of these specimens was simply an abnormal specimen or a new species. Pre-DNA taxonomists classified species predominantly using the morphological species concept (MSC), or using alpha taxonomy, so that abnormal specimens could not definitely be separated from new species because they both differed phenotypically from all previously described forms. It was only the degree of divergence from described forms which separated mutants from subspecies, and any talk of degree is necessarily subjective.

There are therefore many specimens in museums which were assumed to be just such abnormal specimens which did not prove to be morphologically distinct enough to warrant description as a new taxon, but which using modern DNA analysis we now realize actually are "good" species. But given the close physical resemblances of many species within a genus it is easy to see how such confusion arose in the first place. Thus these abnormal specimens, actually new species, simply sat in museums around the world until serendipity intervened and they were recognized for what they really are. Unfortunately, most of the species which have been supposedly rediscovered have been of this nature: specimens held in museums for years, even decades, until it is realized that they are actually new species. Then scientists go on an expedition and "rediscover" it. Species which daily encountered humans, and which were forced into extinction as a result, are invariably never rediscovered. One could therefore say that only a handful of genuine rediscoveries have actually been made, while the rest were never really feared extinct in the first place. It’s just that nobody bothered to look for them, or because nobody knew to (perhaps because of incorrect locality data):

"The status of many tropical species is unknown, because no one has seen them again or specifically looked for them since they were discovered. For instance, among the New Guinea birds that I study, Brass's friarbird is known only from eighteen specimens shot at one lagoon on the Idenburg River between 22 March and 29 April 1939. No scientist has revisited that lagoon, so we know nothing about the current status of Brass's friarbird."1

(Jared Diamond, The Rise and Fall of the Third Chimpanzee, p. 316)

The fact that a species has not been seen in many years is, when considered in isolation from other potential factors, an insufficient indicator of the conservation status of a population. More than 50 years had passed since Brass's friarbird was last seen when Diamond wrote The Third Chimpanzee. And yet nobody even considered the possibility that it could have become extinct in the mean time since it presumably faced no long-term threats above and beyond those of everyday life. Thus, when Brass' friarbird was found again it was a case of relocation and not rediscovery.


But what then is a good indicator of extinction? And hence, what is a good indicator of genuine rediscovery, as opposed to relocation? Of course, if we only declare those species officially extinct for which we have surveyed their entire habitat, or whose habitat has been completely destroyed, then no species will ever be rediscovered. It seems ironic then that for the term "rediscovery" to retain any purpose in the language of conservation biology our criteria for declaring a species extinct cannot be too stringent.

I propose an arbitrary cut-off point to demarcate "rediscovery" from "relocation". This separates species found to still persist after an extended period of time (which is subjective) into two categories:

A. 0-49% chance of the taxon having become extinct. Such taxa should be referred to as having been "relocated" as there was never really any great question over their continued existence, especially for the lower percentages. Though for those percentages approaching 50% there may have been some doubt as to their persistence.

B. 50-100% chance of the taxon having become extinct. Such taxa should be referred to as having been "rediscovered" as there was, at minimum, an equal chance that it had become extinct as that it still persisted, through to a very good chance that they had become extinct during the intervening period during which no confirmed sightings were made.

Clearly 0% and 100% are "impossible categories", contradictions in conservation. No population can be relocated if there was a 0% chance of its extinction since the last record, since the only way in which we could say that there was such a low probability of extinction in the first place (i.e. no chance) was if we had certain knowledge of its persistence into the present. And for 100%, as I pointed out earlier, a species which is definitely extinct (both in the wild and in captivity2) cannot therefore be rediscovered. It can only be brought back through "de-extinction", as it has come to be known.


Unfortunately neither the Dodo nor the Yangtze River dolphin nor the Thylacine, nor numerous other iconic extinct species are ever likely to return to us. They are sadly almost certainly gone forever, as it now seems that cloning the Thylacine is impossible from the fragmented state of DNA in all suitably preserved specimens. A constant reminder of the ignorance we once possessed and are still finding hard to shrug off. Unfortunately it is only when things are gone that you realize how special what you had was. If only that wasn’t true, we wouldn’t be heading towards an ecological disaster of global and bio-historic proportions.

But alas it is true, and it couldn’t really be any other way. Thus, we find ourselves trying to make so much out of so little; trying to reunite all of the various Thylacine artefacts held in museums around the world, hoping that something will change. Even though such an effort is so detached from the possibility of its continued survival that not only do we know it subconsciously, but also consciously. Nevertheless, our guilt drives us to do such things as a part of the grieving process...


1 In case you were wondering, Brass's friarbird has now been found at other locations since Diamond's book was published (1991), though it's population size is still unknown and only a very few records attest to it's existence.

2 It has been suggested in recent years that there are pure bred Barbary lions (Panthera leo leo), originally from North Africa, in zoo collections. However, these claims are doubtful as genetic analysis of putative Barbary lions has failed to substantiate these claims so far.


Diamond, Jared. (1991). The Rise and Fall of the Third Chimpanzee: How Our Animal Heritage Affects the Way We Live (2002 Vintage pb. edition). London: Vintage.

BirdLife International. (2011). Species factsheet: Philemon brassi. Downloaded from https://www.birdlife.org on 17/01/2011.

Published on 20 April 2014