Determining when a species truly disappears has long challenged scientists. A global study found more than 500 species are in flux, uncertain whether they still exist or have vanished.
Species like Sir David’s long-billed echidna, the ivory-billed woodpecker, and Lipotes vexillifer, the Baiji, linger in a state of ambiguity. Their survival could not be confirmed through reliable observations, keeping them in an unsettled category rather than declared extinct.
Officially, the International Union for Conservation of Nature (IUCN) defines extinction as when there is no reasonable doubt that the last individual has died, a verdict that is notoriously hard to verify in practice.
A taxon is treated as extinct when extensive surveys fail to find any individuals in the species’ historical range and in areas of suitable habitat, at times when sightings would be expected.
Decades ago, a proposal suggested classifying a species as extinct if it had not been observed for fifty years. That idea did not gain wide acceptance, and most conservation bodies have adopted a more cautious approach before making extinction declarations.
Many cases show species once labeled extinct being rediscovered after long gaps of time. Examples include two species of coelacanths and other creatures once thought lost, and in one case a Bornean endemic songbird was observed again after 172 years. These rediscoveries highlight the challenges of confirming extinction and the uncertainty that can persist across taxonomic groups.
The false alarm problem
These rediscovery episodes, among others, undermine the clarity of the fifty-year rule. Yet prematurely declaring extinction can also harm conservation efforts, as critical habitats might lose protection once a species is deemed gone.
Similarly, ongoing false alarms can erode public empathy and the scientific community’s confidence in using extinction as a definitive label.
In a related note, a museum specimen of a notable species died in the early 2000s, underscoring the long timelines involved in documenting losses.
Researchers reviewed data on more than thirty thousand species listed on a major global inventory and identified hundreds of species as lost. Findings appeared in a peer-reviewed conservation journal and are used to gauge broader trends in global biodiversity.
The red list places a portion of these lost species in categories suggesting probable extinction, according to experts who emphasize that the extinction crisis is intensifying. The status of many species with uncertain conservation outcomes may pose growing challenges for researchers and policymakers alike.
At the outset, the study began with thousands of species thought extinct or long absent. Some were later rediscovered, shifting the count of truly extinct species downward while revealing others that had not been observed for extended periods.
The analytical process then removed species with very recent last sightings, leaving a core group of hundreds of species whose existence remains in question across amphibians, reptiles, birds, and mammals.
Tropical regions bear the heaviest burden
Since the year 1500, many terrestrial vertebrates have vanished, with tropical regions showing the highest concentrations of losses. Countries like Indonesia, Mexico, and Brazil account for a substantial share of these cases, reflecting the pressures faced by megadiverse ecosystems.
Researchers note this concentration is concerning because it points to areas where future losses are likely to be greatest if protections and monitoring do not improve. The study’s lead author stresses the urgency of enhanced research in hotspots to better verify the status of missing species and to drive targeted conservation actions.
The work highlights the need for more funding to support field surveys and expeditions aimed at confirming whether suspected losses are real or simply gaps in data.
Reference work from a prominent scientific publisher provides detailed methodology and results for those seeking to understand the study’s framework and implications.
End of report.