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It's early January, and Jens-Kjeld Jensen is walking out to a European Storm-Petrel colony on the small island of Nólsoy, a part of the remote Faroe Islands chain in the North Atlantic Ocean. The 73-year-old's eyesight has diminished significantly in recent years, but the slightly snowy, slippery track doesn't hinder the self-trained naturalist. He knows the route instinctively because he has walked it more than 1,000 times since he moved here almost five decades ago.

Nólsoy is only inhabited by 230 people, but what the island lacks in humans, it makes up for by housing a tiny, nocturnal seabird. Around 50,000 pairs of European Storm-Petrels arrive in May to nest in flat areas between stones, making it likely the species' largest colony in the world. The birds, only about six inches long and 15 inches in wingspan, stay for around five months before migrating thousands of miles to the southern Atlantic to spend the nonbreeding season on the open sea. Beyond that, relatively little is known about these secretive, some say mystical, birds. Because of their small size, GPS trackers have only recently become light enough to attach to them.

As we walk carefully, we’re on our way to look at one of Jensen’s recent projects. Really, it’s a tweak of an old invention—the nest box. But it’s helping pave the way for new research that might reveal basic answers about this storm-petrel colony’s behaviors and migrations. The work is only the most recent in Jensen’s years of collaborating with scientists who visit the island to study its bountiful birds. 

“A lot of the work there wouldn't be possible if it wasn't for Jens-Kjeld,” says Anne Ausems, a Dutch scientist who studies the storm-petrels. She first came to Nólsoy because her advisor at the University of Gdansk, like his professor before him, had collaborated with Jensen, who constantly repeated he was only a chef. “He will say he knows nothing, but that's a lie,” she says. 

Educated as a chef in his youth, Jensen first visited the Faroe Islands in 1970 at age 20 while in the Danish Marines. There, he struck up a friendship with Nólsoy's aging ornithologist and bird conservator, Niels á Botni. For several summers, Jensen visited to assist him in stuffing birds. By 1975, Jensen had bought a square yellow house there and gradually took over the business.

Over the years, Jensen accumulated a chamber of natural secrets from the Faroes and beyond. His workshop contains a collection of birds he’s preserved, from owls to gannets. He keeps cockroaches as pets on a shelf that also showcases animal skulls and a model of a dolphin fossil. A binder contains hundreds of species of dry-preserved lice that he’s collected and identified. When a biologist called him from London and asked if he knew how she could get her hands on mice from the Faroes, Jensen told her that he had a few kilos in a freezer— the first collected a year before she was born. “One scientist asked me if he could see my freezer after I die,” he tells me in Danish. "He is convinced he will find something interesting,” he says, and grins at himself. (He knows he isn't like most people.)  

Until 1984, Jensen had mostly been interested in studying Nólsoy’s Atlantic Puffins. But when a visiting scientist was flabbergasted by the storm-petrel numbers living there, he realized how unique the colony was. “I think I must have put bands on 20,000 to 25,000 European Storm-Petrels since then,” he says. Last year, he and Jógvan Thomsen, another resident of Nólsoy, published a with all that is known about the island’s birds from work over decades.

Inspired by the use of artificial nesting structures to facilitate research other breeding colonies, Jensen and Thomsen began building some for the petrels of Nólsoy. Thomsen’s first design intrigued Jensen, but he wasn’t quite satisfied. Jensen knew the birds nest in holes in rocky screes—importantly, he observed they usually picked holes larger than seemingly needed. “I knew how the storm-petrel thinks,” Jensen explains. He concluded the entrances needed to be bigger.

The pair placed the new “nests” made of large plastic tubes between stones and covered them with grass to imitate natural burrows. The results were better than they’d hoped: Of 60 artificial burrows they put up in 2020, eggs were found in 13 of them—and almost all had been visited by a bird within a year. In comparison, of 113 artificial burrows in Skokholm Island in west Wales, only 14 showed signs of occupancy in 2021, eggs were only laid in five, and only three European Storm-Petrel chicks fledged successfully, says Cardiff University researcher Ben Porter.

This success, combined with the recent use of trackers, is aiding new studies of the island’s storm-petrels. For the first time, Jensen and a group of scientific collaborators can put cameras on the nests to observe the birds up-close. The footage has already revealed that nesting adult pairs don’t tightly coordinate their feeding trips, sometimes leaving a chick alone in the nest. The artificial abodes also help them equip and recover GPS trackers from the birds. In 2022, they managed to recover one tracker, which showed that a storm-petrel had traveled to feeding grounds about 100 miles southeast of the Faroes, halfway to Scotland's Shetland Islands, and back in two days.

Porter, one of the scientists Jensen is collaborating in the work, said this preliminary data is interesting because the birds from the colonies in the Shetland Islands also travel southeast away from the Faroes. “Colonies might segregate slightly so that they're not competing or using the same foraging grounds,” he says—though it’s too early to draw conclusions.

As part of his PhD, Porter wants to gauge how growing light pollution affects the breeding petrels, especially fledglings. “They're really easily disorientated by artificial light. So, you can get these big sort of gatherings around light where a lot of them die,” he says. By placing artificial lights in different colors and frequencies close to the colonies, he hopes to understand how the birds respond. Combining that knowledge with the bird’s travel patterns could help the scientists recommend ways to minimize the light pollution risks. 

Another goal of research efforts is to understand how increasing activity on the open sea may affect the seabirds, says Sjúrður Hammer, a biologist at the Faroese Environment Agency and Porter's adviser. Salmon farming companies—one of whom funds some of the studies—hope to start operations far offshore, and the Faroese public power company is also considering offshore wind farms. Meanwhile, the Arctic’s melting ice will be spurring more ship traffic in the region.

As this year’s breeding season approached, Jensen was focused on improving the design by insulating the lids and experimenting with adding small tubes that could provide “air conditioning.” On our visit, he puts matchsticks in the entrance tubes. If later, the stick has fallen, he knows the tubes have been visited by a bird. With his waning eyesight, what amazes him is how the birds can find the well-hidden holes in the middle of the night. “I don't understand it,” he says.

For all his efforts for the wildlife of Nólsoy, Jensen was awarded an honorary doctorate from the University of Faroe Islands in 2015 and the  in 2020, earning him some well-deserved accolades. But he doesn't seem to care about titles and prefers to not be lumped in with what he calls "bread and butter" biologists with fancy degrees. In his mind, despite his tireless commitment and research, he's still "just a chef," happy to continue the same hike he has for decades while working to uncover the European Storm-Petrel's secrets.