Tracking trends in the risk of extinction: 20 years of the Red List Index
A new review paper released today covers the Red List Index, the approach BirdLife pioneered to understand if nature's extinction risk is improving or worsening.
By Dr Stuart Butchart, Chief Scientist for BirdLife International
How do we know whether conservation actions are succeeding, or whether they are overwhelmed by human impacts on nature? While there is good evidence on the impact of conservation for individual species and places, we need to understand the bigger picture and how it is changing. The IUCN Red List is the gold standard in terms of telling us which species are at greatest risk of extinction, which is why BirdLife contributes to the IUCN Red List as the global Red List Authority for birds. But given the complexity of changes in the Red List each time it is updated, it’s not simple to work out whether things are getting better or worse.
The challenge is compounded because the majority of changes in the status of species on the Red List result from improved knowledge. For example, we might find out that a species is rarer or more widely distributed than previously thought and assumed. Furthermore, many changes in Red List category result from taxonomic revisions – when species are split or merged together, resulting in new Red List assessment.
Therefore, the crucial question is how can we use the Red List to understand whether the overall extinction risk of species is improving or worsening? Birds have been assessed for the IUCN Red List for longer and more frequently than any other group, so BirdLife rose to the challenge and led an international effort to solve this problem 20 years ago.
The solution we came up with – called the Red List Index – included two key innovations. Firstly, it distinguishes ‘genuine’ changes in extinction risk: when a species recovers as a result of conservation action or gets closer to extinction because of growing threats. All the cases when a species is moved to a different Red List category because of better knowledge, taxonomic revisions, or corrections of errors are excluded. Secondly, the method accounts for the movements of species between each of the Red List categories, not simply whether species are considered threatened or not. The formula for the Red List Index summarises these complex datasets into a simple number for each timepoint, resulting in a trend line which declines as species are driven towards extinction.
The Red List Index can also show trends for different countries, regions, ecosystems (such as marine or freshwater), groups of species (including pollinators or migratory species) and types of threats (pollution or fisheries, for example). The approach we pioneered for birds has now been expanded to cover amphibians, mammals, corals, and cycads, and multiple other species groups will be added in the next few years. The Red List Index has given us a broader understanding of global biodiversity trends at the species level than any other indicator.
The Red List Index has been widely used to assess progress towards global goals to protect nature, showing that the world failed to meet previous targets to prevent the extinction of species and reduce the loss of biodiversity. It has been adopted as an official indicator for the UN Sustainable Development Goals, for the Global Biodiversity Framework – global goals to protect nature agreed by 195 countries and the European Union in 2022, and for other intergovernmental agreements.
The history of the Red List Index over the last two decades, its origins in BirdLife’s Red Data Books and Red List assessments, and its numerous policy applications have been charted in a new review paper, published today in the prestigious scientific journal Philosophical Transactions of the Royal Society.
Birds led the way as our barometer for the health of the planet – and our scientific research has helped measure that wellbeing in the form of the Red List Index. The human race is responsible for vanquishing other life forms from existence. It is a sobering reality we cannot ignore. However, with the Red List Index tracking charting what is happening to our natural world, we can do something about it and importantly, hold those responsible to account.
