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What is the IUCN red list?

The International Union for the Conservation of Nature was first established in 1948 and today stands as the largest international conservation network. It consists of over 1200 members, ranging from both governmental organisations and NGOs to states themselves. 

The IUCN consists of six commissions, the largest and perhaps most famous of which being the Species Survival Commission, dedicated to evaluating the status of species worldwide - producing, as they do so, the IUCN red list. 

The IUCN red list is an assessment of the status of conservation species and subspecies - specifically, how close they are to extinction. Before 1994, this was largely based on subjectivity - the categories weren’t rigidly defined, and so the status of the species depended in part on the scientist assessing it. 

But new guidelines were developed, and since then the categories have been objective and mathematical, meaning anyone with enough knowledge can assess the status of a species. 

The categories are displayed in the image and are as follows: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened and Least Concern, along with Not Evaluated and Data Deficient. 

Until the 1990s, a species was considered extinct by the IUCN if there had been no sightings of it for 50 years. The definition was then updated - now, a species is considered extinct if there can be “no reasonable doubt” that there are any individuals left. This means that scientists have conducted exhaustive surveys throughout the species’ range without finding any presence of the species. If a species exists in captivity (eg. a zoo) but the surveyors find no trace of it anywhere else, it is thought to be extinct in the wild

After that it gets a little bit trickier and more mathematical. The remaining categories are based on factors like:

  • Population size (with less than 50 individuals said to be critically endangered), 

  • Geographic range and habitat status (if a habitat is highly fragmented and declining it could jeopardise the future of the species)

  • Population decline (both actual and projected) 

  • Quantitative analysis which determines probability of extinction

All of the species assessments on the IUCN red list are a result of contributions of data from thousands of scientists across the globe, and assessments are checked in a review process to ensure that they are accurate. Even then, the IUCN aims to re-evaluate every species at least once every 5 to 10 years in order to ensure its threat category is still accurate. Over 120000 species are categorised on the Red List, with around 27% of those being classed as threatened. 

The list is an incredible amount of effort, but it is worth putting in because of how valuable the Red List is as a tool for monitoring conservation priorities and effects - if population recovery attempts are successful, species can be downgraded to a lesser risk group. 

One example of this is the Asian-crested ibis, once plentiful across Asia until it was hunted to near-extinction for its feathers - in fact, it was considered to be completely extinct until it was re-discovered in the wild in 1981. When found, it was evaluated as Critically Endangered by the IUCN, down to just 2 breeding pairs in the Shaanxi province of China. 

Conservation efforts began, including the prohibition of hunting, logging and use of agrochemicals near its feeding and nesting habitats, its nesting trees being declared official state property. It consequently increased from those 2 remaining breeding pairs in 1981 to 70 pairs in 2001, by which time it had been reclassified as Endangered. The species has a long way to go, but it is on the road to recovery. 

The Red List guides both scientists and politicians in conservation and policy planning. One example of this is its use to determine where to locate Key Biodiversity Areas (KBAs) - areas which contribute significantly to global ecosystems and biodiversity. Once a KBA is designated, pressure can be exerted on governments to legally protect it, and on the private sector to avoid exploiting it. 

One primary issue with the IUCN red list as it stands is its bias for vertebrates, specifically mammals and birds - a small slice of the biodiversity of the planet, which is vastly made up of plants, fungi, invertebrates and lower invertebrates. The IUCN is working on improving this though, with aim to conduct more global assessments, particularly within different geographic and taxonomic ranges. 

Red list assessments also do not account for factors like the feasibility of conservation efforts, the cultural and economic significance of species, and national policy legislation, all of which may affect the conservation of a species. 

Despite this, the Red List has achieved worldwide fame and respect within the scientific community, and for good reason. Acting as a “barometer of life”, the list presents a stark reminder of our future: one where the ceaseless, futile exploitation of our planet has eradicated the beauty of biodiversity which nature has to offer us. 


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