Weasels, not pandas, should be the poster animal for biodiversity loss

At the UN Biodiversity Conference that opens in Montreal on December 7, 2022, nations aim to create a new global framework to transform humanity’s relationship with nature. The conference logo depicts a human reaching out to kiss a panda – but from an ecological perspective, a weasel or a badger would be a more appropriate choice.

Widespread large mammals, also known as charismatic megafauna, often represent the greatest achievement in biodiversity protection. Logically, saving the tiger, polar bear, wolf or lion means saving an entire ecosystem, as these species often have large ranges and can be at the top of food chains.

But research shows that, relatively speaking, many large, charismatic species aren’t faring so badly in North America. Wolves are repopulating California, where their last wild ancestor was killed in 1924. Cougars could reestablish themselves in the Midwest in the coming decades. Black bears have regained much of their range in the eastern United States, to the point that many states have a bear hunting season. Similar stories unfold across Europe, where even large carnivores like lynx and wolverine are recovering.

For small carnivores like weasels, skunks and foxes, it’s a different story. These species and their relatives have equal or greater impacts on the ecosystems they inhabit than larger species like wolves. They even provide benefits to humans by preying on rodents that eat crops and infest our homes. Yet small carnivores are of growing conservation concern as their populations decline dramatically in many places.

Many threats but no single cause

While small carnivores generally don’t get as much public attention as larger species, conservation biologists have been trying to halt their decline for decades.

For example, the black-footed ferret, a member of the same family as weasels and mink, has been on the U.S. list of endangered species since the list was created in 1973. As recently as the early 1900s, it there were thousands of American polecats. across the western prairies. Today, scientists estimate that there are less than 400 left in the wild.

Recent evidence suggests that even the most common and widespread small carnivores are in decline. A 2005 study estimated that eastern spotted skunks, which are rarely seen today but were historically found in much of the United States east of the Rocky Mountains, had declined in numbers by 90% over the previous 50 years.

I led an effort in 2021 to determine the status of the most widespread of small carnivores in North America – weasels. We found range-wide declines dating back to the 1960s that matched the decline of spotted skunks.

Scientists have a very poor understanding of what caused the losses of weasels and most other small carnivores. We suspect that many stresses may be involved, including changing agricultural practices, disease, and new carnivores like house cats, house dogs, raccoons, and striped skunks that follow human development and outgrow or eat native small carnivores.

What we do know is that North America is not unique. Small carnivores are declining worldwide at an alarming rate. A 2021 review suggests that over the past two decades more than half of all small carnivores have declined in number and a quarter are threatened with extinction. Proportionally, these are the same levels of decline and endangerment as the best-known threats to large carnivores.

Short-legged ecosystem indicators

We also know that compared to larger species, small carnivores have shorter lives and use smaller areas. This allows them to react quickly to even minor temperature fluctuations, habitat changes, and food availability. In my research over the past 23 years, I have learned that these attributes make small carnivores sensitive indicators of even minor changes in the functioning of their ecosystems.

A prime example comes from the Channel Islands off California, home to the lesser island fox, a species found nowhere else on earth. In the late 1990s, land and wildlife managers noticed a decline in island foxes, which coincided with the decline of bald eagles and the arrival of golden eagles on the islands. Golden eagles hunted foxes, as well as non-native wild pigs. At one point, the fox population was reduced to less than 100 individuals.

The island fox restoration was a complex endeavor that involved reintroducing bald eagles – which feed on fish, not mammals – to the islands to hunt golden eagles; eradicate introduced pigs, which served as food for golden eagles and altered the vegetation where foxes sheltered; restore shrubs and grasses; and raising foxes in captivity and then releasing them. This effort is one of the most significant examples of intervention by biologists to reverse the slide of a species towards extinction.

More broadly, the story of the island fox shows that small carnivores can provide unique insight into ecosystem structure, as they are at the center of food webs. Look at the diet of a fox or a weasel and you will get a great insight into the number of species present in this ecosystem.

The loss of small carnivores can alter ecosystems. Many small carnivores typically feed on small, seed-eating rodents like mice and gophers. This reduces the impacts of rodents on plants and agricultural crops. It also helps reduce the spread of tick-borne diseases, as small rodents can serve as hosts for infected ticks.

For these reasons, I and other ecologists argue that it makes sense to use small carnivores as barometers of ecosystem health. That would mean replacing polar bears with weasels as poster animals for global warming, and grabbing ocelots rather than jaguars to understand how rainforest destruction is affecting wildlife.

While lions and polar bears are important, I think ferrets, weasels and foxes deserve the same kind of protection and are a more accurate tool for measuring how ecosystems are responding to a rapidly changing world.