Holding out hope: Why these scientists haven’t stopped looking for their favorite most wanted lost species

In light of the extinction crisis threatening biodiversity around the world, it may be easy to lose hope that any species not documented by humans in years — or even a century — still lives among us. However, Re:wild’s Search for Lost Species program reveals that the truth is murkier. Since making a list of 2,200 lost species that scientists believe may still be hiding (albeit usually in low numbers) in dense swamp forests, remote islands or even beachside golf courses and backyards, Re:wild has organized and supported searches across the globe, some spanning years and country borders.

“Finding a lost species is not an easy task,” says Barney Long, Re:wild’s senior director of conservation strategies. “In fact, some of these species may not be found again.” But as recent rediscoveries of animals such as the Fernandina Galápagos Tortoise and the Silver-backed Chevrotain attest, there are reasons to be optimistic that many of these species are still out there. Here are a few of them.

1) Challenging field conditions make it difficult to search, but don’t mean the species is gone.

Many factors can complicate searching for lost species. Despite all the logistics planning required for any one of these expeditions, researchers can often only spend a few days or weeks in the field at a time, which doesn’t leave much room for error. And, as Long says, “Any species that has not been seen for 10 years is either going to be hard to find because it blends into its habitat well, naturally very rare, or living in a very remote location.

For example, the Namdapha Flying Squirrel (Biswamoyopterus biswasi) is known from one specimen found in India in 1981. As a result, scientists know next to nothing about its ecology or behavior. Assuming the species is similar to other flying squirrels, it is likely nocturnal — and while it’s already tough for researchers to spot an animal high in the forest canopy, it’s that much harder in the dark.

Similarly, the Omeltemi Cottontail Rabbit (Sylvilagus insonus) is known from only four individuals captured in the early 1900s in a small mountainous area of Mexico. The initial survey method also proved challenging for the researchers.

“Camera traps put out for the species recorded many rabbits,” Long says. “But poor-quality, black-and-white photos made it impossible to tell if we were seeing the lost species or the very similar-looking rabbit species commonly seen in the area.”

Sometimes the terrain itself poses difficulties, as in the forests of southeastern Côte D’Ivoire where scientists have been searching for Miss Waldron’s Red Colobus (Piliocolobus waldroni), which, if declared extinct would hold the tragic distinction of being the first known primate extinction in 500 years.

“The biggest challenge was overcoming the fear of entering this moving mud forest in places that were described as infested with crocodiles and snakes,” says André Koffi, a researcher at the Swiss Center for Scientific Research in Côte d’Ivoire who led the surveys. “At the start of our investigations, very few individuals from local communities dared to venture there except some poachers.”

Other times, humans present the bigger threat, particularly in the search for the Omeltemi Cottontail Rabbit.

“The initial survey area became dangerous due to criminal activity, and night searches with flashlights just became too silly of an idea,” Long says. “We don’t want to put anybody at risk.”

In Venezuela, the hunt for the Scarlet Harlequin Frog (Atelopus sorianoi) has encountered many logistical obstacles.

“Most of the challenges have to do with the sociopolitical problems in the country, which makes it very difficult to follow planned searches,” says Enrique La Marca, the biologist leading the search. “Along with this is the deteriorating situation, which makes it difficult to find gasoline or diesel for the vehicles and keeps worsening the proper maintenance of roads.”

Meanwhile in Colombia, researchers were unable to look for the Sinú Parakeet (Pyrrhura subandina) until 2016 due to armed conflict in the forest region where it was last seen — and as the January 2021 murder of Colombian parrot conservationist Gonzalo Cardona Molina grimly illustrates, environmental defenders continue to put their lives on the line to do this important work.

2) Anecdotal sightings by local communities indicate that at least some of these species still exist.

Long before they were “discovered” by Western scientists, many species around the world were well-known to the people living nearby. Even if it’s been years since a scientific expedition has officially observed these lost species, local residents have claimed that some of these species are still out there — because they’ve seen them.

For example, when searching for the Syr Darya Shovelnose Sturgeon (Pseudoscaphirhynchus fedtschenkoi), Bernie Kuhajda of the Tennessee Aquarium
says local interviews were key.

“We interviewed several fishers when we were in Kazakhstan, and two of them described catching a fish that could be nothing but the Syr Darya Sturgeon in the last five years,” Kuhajda says.

The species is among the world’s smallest sturgeon species and doesn’t get more than about a foot long; it is thought to be threatened by damming of its native waterways, which makes it harder for fish larvae to survive.

The Pink-headed Duck (Rhodonessa caryophyllacea) — last documented in India in 1949 — may have been spotted by locals at Myanmar’s Indawgyi Lake during the rainy season as recently as 2010. Although this species was probably never common, its distinctive coloring should make it easy to identify; unfortunately, the remote wetland is largely inaccessible to foreigners and requires special permission to visit, a circumstance that has made it difficult for a team of researchers to confirm the sighting. Still, reports like this give hope to Richard Thorns — a British researcher who has been leading the search for the duck for more than two decades — and make him feel that his team is closing in on the truth about this bird.

3) New research methods could hold the key to rediscovery.

Technological innovations are giving scientists more ways than ever before to identify the presence of species — though each method has its pros and cons. Long describes how the search for the Omeltemi Cottontail Rabbit changed tactics after the camera traps’ limitations became clear.

“The search has now shifted to DNA sampling from dung, which, while much safer and less difficult, is much more expensive,” he says.

In South Africa, the team looking for De Winton’s Golden Mole (Cryptochloris wintoni) went a step further as they searched for this species of “sand-swimming mole” that leaves no tunnels behind in the ever-shifting sand. Collecting more than 100 sand samples from potential mole trails and testing them for environmental DNA (eDNA) (this is where you detect mere fragments of DNA left behind as an animal sheds cells) has led to either the discovery of a new species or the rediscovery of the lost species and the team is still working on analyzing their findings.

Of course, sometimes reviving older survey methods is worth a try. After conducting several searches for the Pink-headed Duck using dugout canoes to navigate the dense swamp in India and Myanmar, Thorns realized that birds frequently flew away when they saw the boats approaching. On the 2017 Myanmar expedition, the team switched to a method once favored by Victorian-era tiger hunters: patrolling the floodplains on the backs of elephants. Not only does this make the terrain easier to navigate, but one of the recent (unconfirmed) sightings of the duck was made by a person traveling by elephant, implying that the ducks don’t flush when the animals approach. Unfortunately the duck wasn’t found on the 2017 expedition, so for future surveys, Thorns will pivot survey methods again and focus on setting up camera traps that nearby community members will be monitor in order to have more “eyes” on this remote wetland.

4) Searching for species can bring new insights that strengthen the case for expanding protection of vital ecosystems.

Even if they haven’t (yet) resulted in finding the species in question, many expeditions have led to other discoveries. For example, in four years of searching for Miss Waldron’s Red Colobus in Côte d’Ivoire’s Tanoé-Ehy Forest, researchers captured footage of other rare primates, including the Critically Endangered White-thighed Colobus, Endangered White-naped Mangabey, and the first-ever video of a Critically Endangered Roloway Monkey in the wild.

In addition to being a refuge for rare wildlife, “the mud from this swamp forest plays an invaluable role in carbon sequestration and is therefore a real carbon bomb,” Koffi says. “If this forest were to disappear, it would release the sequestered carbon … so we are fighting not only for the protection of rare species but also and above all for the sustainable conservation of this forest.”

Similarly, the March 2021 expedition searching for the Sinú Parakeet found 22 bird species never before documented by scientists in the Córdoba department of Colombia.

If scientists rediscover the Scarlet Harlequin Frog in Venezuela, its continued existence could provide a crucial clue to how species can survive the chytrid fungus, a deadly illness that has decimated amphibian populations worldwide. In Kazakhstan, rediscovering the lost sturgeon would be a promising indicator for aquatic biodiversity health in an ecosystem that has been imperiled by human interference.

“Rediscovering the Syr Darya Shovelnose Sturgeon would be the impetus for creating a hatchery program to bring the species back from the edge of extinction,” Kuhajda says.

And in the Philippines, searches for the Ilin Island Cloudrunner (Crateromys paulus) have inspired more local interest in the endemic rodent species.

“I think the best part is, we elevated the interest of our volunteer forest rangers to continue their patrolling in the area, and to search for the species during their patrolling even if we are not with them,” says Kyle Cielo, the research program manager for Mindoro Biodiversity Conservation Foundation.

5) Optimism is essential for success.

Curiosity is a major driving force behind some of humanity’s biggest discoveries, from traditional knowledge to life-saving medicines to space exploration.

Without this urge to discover the unknown, the search for the Pink-headed Duck may have never happened. In 1998, Thorns was on his lunch break while working in a U.K. department store, looking through a book about disappearing bird species.

“I thought the Pink-headed Duck was the most beautiful thing I had ever seen in my life,” he says. “I walked into the staff canteen a menswear sales assistant and walked out a pith-hatted explorer.”

More than 20 years later, that burst of inspiration continues to fuel Thorns’ passion as he organizes searches for this elusive species.

As determined researchers face the many obstacles of field work, optimism is critical to keep their motivation up — and to allow for any chance of success.

“Hope has to spring eternal when you work with imperiled aquatic species,” Kuhajda says. “It is the only future that I let myself imagine!”