It finally stops snowing just as Tiit Maran parks his orange Dacia Duster next to a bridge on a quiet country road. “Too bad the snow is so fresh,” he says. “We’ll not find any tracks now.” Maran, the director of Tallinn zoo and a European mink biologist, is looking for the critically endangered mammal on an Estonian island. Along a straight, ice-free stream, he clambers over fallen trunks, his boots sinking into the powder snow. A glorified chicken coop comes into view, one of the three sites where Maran’s team regularly released European minks between 2000 and 2016. Pregnant females were placed in the cages in May, allowing the mink and her brood plenty of time to adapt to the smells and the sounds of the forest before the doors swung open in August. Hiiumaa is Estonia’s second-largest island. Its natural borders, surrounded by the Baltic Sea, sparse population and limited surface area – it is just 989 sq km – make it a place with enough potential for the reintroduction of the European mink, which had been locally extinct in Estonia since the mid-1990s. At one time, the European mink (Mustela lutreola), a small semiaquatic predator that belongs to the family of weasels, otters and martens, was found almost everywhere in Europe, from the eastern foothills of the Urals to northern Spain, from Finland to the Caucasus. But its downfall in large swaths of Europe started centuries ago. Scientists struggle to pinpoint one cause of its demise. More likely, a confluence of circumstances pushed the species towards the abyss, all of them driven by humans. The wetlands in which minks thrived were drained, rivers were straightened, their habitats poisoned. And their furs ended up in wardrobes all over the continent. The final blow came with the farming of their distant cousins from across the water, the American mink. The animals regularly escaped the industrial-sized farms – or activists opened their cages. In the Soviet Union, scientists released American minks intentionally into the wild, with the idea that they would enrich the fauna. Similar in appearance but not closely related, the two species target the same ecological niche. But the European mink is no match for its shrewd, more flexible and aggressive American counterpart. The American mink drove the European mink to inferior habitats where it found less food and failed to reproduce successfully. The International Union for Conservation of Nature (IUCN) considers the European mink one of the most endangered carnivores in Europe. Within the EU, the animal survives in small numbers in Spain, France, Romania and Estonia. The American mink, on the other hand, thrives in about 20 European countries. Ecologists continue to protect the remaining habitats of the European mink from dangerous invaders. In Spain, where the European mink occurs in Basque country, Navarre, and La Rioja, government agency Tragsatec traps American minks that enter the habitat of the European. Without these measures, says Madis Põdra, an Estonian biologist living in Spain, the European mink would already be locally extinct. “American minks spread fast. Active management is the only way for the European mink to survive.” At Tallinn zoo, biologists are monitoring the gene pool of the European mink. The breeding facility is currently sealed off as Covid-19 can have disastrous consequences for minks – more than half of Europe’s captive minks live in Tallinn and an outbreak would be catastrophic. “We’d lose the backbone of our conservation work,” says Maran. When the animal disappeared from the Estonian wilderness, Maran plotted to repopulate Hiiumaa with captive-born European minks. Trappers first eliminated the American minks that had escaped from a now defunct fur farm on the island and, in 2000, Maran’s team released the first batch of European minks. The reintroduction did not go smoothly. Most males born in captivity showed no interest in mating, even behaving aggressively towards their partners. “In certain years, 80% of males failed to produce offspring,” Maran says. “With every male that does not contribute to the next generation, genetic diversity gets lost.” More than 500 released minks later, the population has finally stabilised. Currently, between 160 and 250 minks populate Hiiumaa in autumn, a number that dwindles to less than half after winter. Islands such as Hiiumaa are typically vulnerable habitats for threatened species. Small populations are acutely sensitive to extinction – environmental disasters, forestry and agriculture or an exceptional winter can have detrimental effects. But islands, besides being centres of extinction, can also become beacons of hope, refuges for species that struggle elsewhere. Maran mentions his former teacher in Moscow, who in the 1980s released minks on the Kuril Islands, a Russian archipelago in the far east. “Those populations still survive 40 years later,” he says. Nature reserves delimited by industry or mountains can also act as islands. This summer, Maran’s team plans to release minks on Saaremaa, Estonia’s largest island. “It’s not very smart to keep your eggs in one basket,” he says. “Two baskets, in combination with breeding at the zoo, will better ensure the future of the European mink.” Although no longer regularly working in the field, Maran tries to enhance the mink’s survival chances by educating people at the zoo. Environmental protection, he says, can be divided into two timeframes – short- and long-term. “The reintroduction of the mink is a short-term thing, even though I have devoted my whole life to it. But if we as humans don’t change, then it has all been useless in the end.”