Biological fieldwork can be grueling—and often dangerous. Countless researchers and support staff have died in the pursuit of knowledge that could protect vulnerable places and species, and enable people to live safer, healthier lives.

Journalist Richard Conniff, author of The Species Seekers, has compiled a “Wall of the Dead” on his blog to memorialize scientists, naturalists, and conservationists killed in the field. We’ve picked out just a handful of the dozens of names from that list. They are people whose passion and dedication to their profession ultimately cost them their lives. In some cases, they anticipated the risks. In others, they most definitely did not. Visit Conniff's full list for a fascinating, and often somber, dive into the lives of these explorer-naturalists.

1. MARGARITA METALLINOU // ZAMBIA, 2015

Margarita Metallinou, a 29-year-old evolutionary biologist and herpetologist, had been working in Zambia’s Kafue National Park, studying the impacts of climate change on the area’s reptiles. While in the field with two colleagues one afternoon, she suddenly spotted an elephant charging toward them. Her scream warned the others, who were able to outrun the elephant. But Metallinou was trampled to death.

2. DIAN FOSSEY // RWANDA, 1985

Who killed Dian Fossey? The 53-year-old American primatologist studied and protected mountain gorillas on the Rwandan side of the border with a passionate love and ferocity that no one disputes earned her many enemies. Yet her 1985 murder in the Virunga Mountains remains unsolved more than 30 years later.

Fossey was known for confronting poachers, even going so far as to kidnap the child of a tribesman who had snatched a baby gorilla (both the child and gorilla were returned unharmed). One of Fossey’s student researchers and a former employee were ultimately charged with her murder. The student fled back to the United States; convicted in absentia by a Rwandan court after only a 40-minute trial, he has long insisted that he was a scapegoat. The tracker was later found hanged in his jail cell. But other theories emerged in the years following her death that cast suspicion on political elites involved in animal trafficking and those threatened by her opposition to ecotourism, which she feared would be detrimental to the endangered gorillas.

Fossey is often credited with bringing the plight of the mountain gorillas to the public. Through her research and engagement with media, she generated sympathy for gorillas and showed people that they were not the savage, violent beasts they’d been portrayed as, but curious, human-like creatures. Fossey’s legacy continues in the nonprofit conservation organization she founded, the Dian Fossey Gorilla Fund International. Three years after her murder, Fossey’s story was brought to the big screen in the 1988 film Gorillas in the Mist, starring Sigourney Weaver.

3. JOHN CASSIN // UNITED STATES, 1869

A leading 19th-century ornithologist, John Cassin described nearly 200 bird species, several of which bear his name. He authored several volumes on birds identified in his travels, from North America to Chile to Japan. Cassin was a methodical taxonomist, working tirelessly as curator of the Philadelphia Academy of Natural Sciences. He died at 55—not due to some misadventure in the field, but from arsenic poisoning, the result of decades of handling bird skins preserved with the chemical.

4. SAFARI KAKULE // DEMOCRATIC REPUBLIC OF CONGO, 2009

In some places, conservation work is inherently dangerous. That’s certainly the case for the Congolese park rangers who protect endangered gorillas in Virunga National Park as violence flares endlessly around them. Since the 1994 Rwandan genocide prompted more than a million refugees to flee across the border and plunged the Congo into conflict, the park has been caught between armed groups seeking control of territory and generating revenue from deforestation, illegal crops, and poaching.

The rangers here do what’s been described as the most dangerous conservation job in the world: At least 140 have been killed in the past two decades, while hundreds more park staff and their families have been displaced. One of those killed was Safari Kakule, a young ranger who colleagues say showed the characteristic dedication of Virunga rangers determined to defend imperiled gorillas and other vulnerable wildlife despite low wages and constant danger.

In 2009, rebels attacked a ranger station in a section of the park that served as a refuge for 18 endangered eastern lowland gorillas. They killed the 33-year-old Kakule, shown here observing a male gorilla in the field the year before his death.

5. JEAN BAPTISTE AUGUSTE ETIENNE CHARCOT // ICELAND, 1936

Jean Baptiste Charcot left his career as a physician to become an oceanographer and polar explorer; this transition was made easier by the inheritance he had received from his father. At a time when interest in the polar regions was increasing, Charcot made several expeditions to the Arctic and Antarctic. He charted South Pole islands and led a series of summer expeditions to the Arctic. In September 1936, at age 69, he was shipwrecked off the coast of Iceland during a storm. Only one man survived; Charcot perished along with more than 30 others.

6. JOY ADAMSON // KENYA, 1980

Millions of fans know conservationist Joy Adamson from her 1960 bestselling memoir Born Free and its subsequent film adaptation. The book and film chronicle how Adamson and her game-warden husband, George, raised an orphaned lion cub at a Kenyan national park and eventually reintroduced it to the wild to save it from being removed to a zoo. The book and film helped shift public opinion about lions from dangerous predator to noble, imperiled creatures. It also stirred some controversy about the ethics of returning a semi-tamed animal to the wild.

Joy Adamson’s life ended violently at 69: she was found murdered at her camp in Lake Naivasha, not far from Nairobi in the Great Rift Valley. A former employee, a teenager named Paul Nakware Ekai, confessed and was convicted of the crime. Almost a quarter of a century later, Ekai claimed he had acted in self-defense after Adamson shot him in the leg. He claimed he had been tortured into confessing. But the following year, Ekai changed his story again, denying any involvement in the murder.

Nine years later, her husband and his two Kenyan assistants were shot and killed by poachers who ambushed their Land Rover.

7. GREGORY FELZIEN // UNITED STATES, 1992

For most of the 20th century, federal predator control programs all but eliminated mountain lions [PDF] from Yellowstone National Park. But by the 1990s, a small mountain lion population had reestablished itself in the park. Gregory Felzien, a 26-year-old biologist, was part of a University of Idaho team studying the lions. He was killed in February 1992—not by a lion, but in an avalanche.

Felzien had snowshoed to the base of Mount Norris in pursuit of a radio-collared mountain lion he was studying. According to the book Death in Yellowstone, Felzien paused in a steep drainage when the avalanche, 100 yards long, 10 yards wide and five feet deep, buried most of his body. He died before rescuers reached him.

8. PLINY THE ELDER // PRESENT-DAY ITALY, 79 CE

Roman military commander and naturalist Pliny the Elder produced several major writings, the most famous of which is the 37-volume Natural History. This expansive set of texts includes vast explorations of astronomy, geography, zoology, botany, geology, and medicine. The encyclopedic collection was a mixture of fact, observation, and superstition, but for centuries it was considered the authoritative text on the sciences (until the scientific method called into question its more speculative conclusions).

Pliny was commanding a fleet in the Bay of Naples in 79 CE when word arrived of a strange cloud emanating from Mount Vesuvius a short distance away. It turned out to be the massive volcanic eruption that destroyed the towns of Pompeii and Herculaneum. Pliny took to the shore to investigate and rescue a friend. He was killed by the powerful volcanic gases (or possibly a heart attack). He was 56.

9. NOEL KEMPFF MERCADO // BOLIVIA, 1986

On the fateful September day in 1986 when Noel Kempff Mercado landed in the Amazon Basin near the Bolivian border with Brazil, he and his colleagues thought they’d arrived at an abandoned air strip. The 62-year-old Mercado was a prominent Bolivian biologist and conservationist. He had traveled to the remote province to explore the newly-designated Huanchaca National Park, a vibrant wilderness area that contained an abundance of biodiverse habitats largely unknown to the outside world. Kempff Mercado had long advocated for its protection.

But the abandoned airstrip turned out to be a cocaine factory, and its guards killed Kempff Mercado along with a colleague and the pilot of their plane. The incident followed on the heels of scaled-up operations against cocaine labs by Bolivian authorities and U.S. Drug Enforcement Agency officials, and there was speculation that the guards had mistaken the men for law enforcement. The murders led to a public outcry, and two years later the park was renamed the Noel Kempff Mercado National Park in honor of its fallen champion. In 2000, it was designated a UNESCO World Heritage site.

10. RALPH HOFFMAN // UNITED STATES, 1932

Born and raised in the Berkshires of western Massachusetts, Ralph Hoffman moved to California and directed the Santa Barbara Museum of Natural History from 1925 to 1932. He was an ornithologist and avid plant collector who made dozens of collecting trips to the Santa Barbara Channel Islands, sometimes dubbed the “North American Galapagos” for their incredible plant diversity and endemism.

Hoffmann made many important contributions to the understanding of the islands’ unique ecosystems, and probably would have made many more. But on a summer day in 1932 while collecting on the remote, windswept island of San Miguel, Hoffmann fell to his death from a cliff.

11. DAVID DOUGLAS // HAWAII, 1834

The Douglas fir is one of about 80 flora and fauna named for David Douglas, the son of a Scottish stonemason who transcended his humble origins to become a highly regarded and prolific botanist. He left school at 11 to begin working as a gardener on a series of large estates. At the age of 20, Douglas was appointed to the botanic garden at Glasgow University, where he befriended leading British botanist Sir William Jackson Hooker. He became Hooker’s assistant, and Hooker later got him a job as a botanical collector for the Royal Horticultural Society.

Douglas made three collecting trips to the Pacific Northwest and California. In 1833 he sailed to Hawaii, enthusiastic to continue documenting the endemic plants of the islands he had first encountered three years before. It was to be his last expedition. While walking one morning en route to Hilo, Douglas apparently fell into a deep pit covered over with dirt and brush, commonly used at the time to trap wild cows. It appeared that the 35-year-old Douglas, who had poor eyesight, went crashing through, where he was crushed and mauled to death by a bull who had also fallen into the pit.

Some have speculated that Douglas was actually murdered. Suspicions fell on the shady former convict with whom Douglas had met earlier that day, but the charge remains unproven. Douglas was buried in Honolulu, and the place where he died is now called Kaluakauka, translated as the “doctor’s pit.” There is a memorial to Douglas on the island of Hawaii and in the churchyard of the Scottish village of Scone, where he was born.

12. ABEL FORNES // ARGENTINA, 1974

Fornes was part of a scientific team trying to prevent the spread of bovine rabies by controlling populations of disease-carrying vampire bats. As Fornes was collecting bat specimens roosting in a water well he had treated with cyanide gas, his gas mask leaked and he fell to his death.

13. ULDIS KNAKIS // USSR (PRESENT-DAY REPUBLIC OF KALMYKIA, RUSSIA), 1970

For thousands of years, the saiga antelope have roamed across the harsh terrain of the Eurasian Steppe, migrating by the tens of thousands between summer and winter pastures. Today they are critically endangered, largely due to oil and gas exploration, road construction, the encroachment of domesticated livestock and illegal poaching for their meat and horns, which are used in traditional Chinese medicine.

Uldis Knakis was a young Latvian biologist who devoted his life to studying and protecting the saiga. The week before he turned 31, Knakis was shot and killed by poachers unhappy with his efforts to crack down on illegal saiga hunting. The murderers were never identified.

14. FERDINAND STOLICZKA // INDIA, 1874

Ferdinand Stoliczka, a Czech paleontologist, geologist, and naturalist, participated in several expeditions to the Himalayas. During a time of heightened tension between the Russian and British Empires, Stoliczka was selected to participate in an enormous diplomatic expedition to Central Asia’s Chinese Turkestan (today the Xinjiang Uyghur Autonomous Region) that required thousands of horses and porters. He did not survive this final trip.

The expeditionary team succeeded in reaching their destination in Turkestan, but on the way back, the 36-year-old Stoliczka began to feel ill. He had extreme breathing difficulties and terrible headaches that intensified as they reached the barren Karakoram Pass, which straddles India and China at an altitude of 18,000 feet. According to accounts from others in his party, Stoliczka had frequently suffered from severe headaches during their mountain journeys. But this time, acute altitude sickness overwhelmed him. He died on the pass and was buried in Tibet.

15. KEITH CLIFFORD BUDDEN // AUSTRALIA, 1950

Only 20 years old, amateur herpetologist Keith Clifford Budden was in a remote part of Queensland searching for an extremely venomous snake, the coastal taipan. The snake is often described as the most dangerous snake in Australia, and although it prefers to slither away, when it feels threatened, it is prone to attack with a series of snapping bites.

Budden successfully caught the snake with his bare hands. But as he maneuvered it into a bag, the snake struck his hand. The following day he died from the powerful venom, which attacks the nervous system and interferes with blood’s ability to clot. Budden’s death was not completely in vain, however: researchers were able to “milk”—extract venom—from the live snake, a first step in creating the anti-venom necessary to treat victims of the coastal taipan.