What’s happening? The US Fish and Wildlife Service (FWS) has declared a further 23 species, including 11 birds and two fish, extinct. Human behaviour was the final cause of the extinction for the newly added species, FWS confirmed. Factors cited included water pollution, the killing of birds for their feathers, and logging. (BBC)

Why does this matter? In 2019, a landmark UN report found that one million species are at risk of going extinct in the next decades. Since then, there has been a lot of discussion about the drivers and impacts of the sixth mass extinction – an extraordinary event in the planet’s history caused entirely by human activity. However, this focus on long-term trends perpetuates the idea that extinction is a slow gradual process that does not require immediate action – a dangerous misconception.

Reality check – The truth is, the scale of our biodiversity crisis is much bigger than the loss of individual species. Researchers studied changes in population size of 4,300 vertebrate species between 1970 and 2016 and found their populations shrunk by 68% on average. In the American tropics, the loss was as high as 94%. Since the dawn of civilization, humans have wiped out 83% of all wild mammal biomass on Earth and about half of all plants. Given the scale of this problem, urgent action is needed to protect natural habitats – waiting until individual species are officially declared endangered is too late.

A second overlooked issue is the risk of extinction cascades. Extinction cascades are domino effects triggered by the disappearance of a single species. A classic example in ecology is the loss of the sea otter in the Commander Islands. In the 18^th century, the animal was hunted to extinction, which led to an explosion of sea urchin populations, the otter’s primary food. The sea urchins overgrazed the local kelp forests which ultimately caused the disappearance of the Steller sea cow, a giant sea mammal which depended on kelp for its survival. A 2017 study found such trophic cascades will become more common in the future as ecosystems become less complex and the loss of one species cannot be compensated by another.

Life-or-death decisions – This isn’t an argument to stop trying to save animals and plants that are threatened by extinction today. With current rates of extinction between 100 and 1,000 times higher than in pre-human times, conservationists are already struggling to keep up. Due to limited resources, however, scientists working in this field are often faced with difficult decisions. Which species are worth saving – and which ones are not?

For a long time, conservation campaigns were centered around charismatic flagship species such as tigers or penguins, as people are more inclined to donate for the protection of these animals. Yet researchers have argued the most beautiful animals are not always the ones with the greatest ecological value.

On the edge of existence – Experts from the Zoological Society of London have come up with a different approach: the EDGE system. EDGE stands for Evolutionary Distinct and Globally Endangered and focuses on endangered species with a long evolutionary history and few close relatives. According to the method, which is based on a species’ position on the evolutionary tree (phylogeny), the most evolutionary distinct mammal is the aardvark while the most distinct bird is the oilbird. Coupled with data from the IUCN Red List, the result is a scientific prioritisation system for conservationists. It might not be able to save all species, but at least it can preserve the overall shape of the tree of life.