Watch the elusive world of the rainforest canopy at night

In the pitch darkness of 3 a.m., ecologist Lucy Hughes stands on a portable metal platform 50 feet up a tree in Panama’s Cocobolo Nature Reserve, scanning the rainforest around her with thermal binoculars. Looking directly into the forest canopy at eye level, she’s able to spot creatures that few other scientists have seen alive in the wild. 

On this night, she’s watching a pair of Andean porcupines (Coendou quichua). At first, the animals appear as fast-moving white blurs through her binoculars, which detect body heat. She watches them dart nimbly along leaf-covered branches, until they step onto a bare limb and “finally reveal themselves,” says Hughes, who’s based at Edinburgh Napier University and the nonprofit Conservation Through Research Education and Action in Panama. 

She can now see their full silhouette, including a bulbous nose and the prehensile tail they use to grasp thin branches. She watches them forage together on bark and leaves, then one playfully chases the other, a prelude to mating. 

It’s a rare and surprising encounter. Andean porcupines, who weigh about 4 pounds and only move at night through rainforest canopies, are so rarely spotted that scientists haven’t been able to determine how endangered they are, and the International Union for Conservation of Nature lists the species as “data deficient.” Scientists previously thought these porcupines were largely solitary animals, but Hughes now concludes, “They’re more social than we knew.”

In fact, many nocturnal rainforest critters are data-deficient because it’s rare to observe them in the wild. But Hughes and other scientists hope to change that. By foisting themselves into the canopy at night to observe the animals at eye level through thermal binoculars, the team has recorded the first up-close, extended video of certain elusive small nocturnal rainforest animals moving in the wild. These include the Andean porcupine and the Panamanian night monkey (Aotus zonalis), a species that is near threatened with extinction. They also tracked kinkajou, margays, olingos, and other nocturnal critters. A study detailing their method, which they’ve tested in Panama and Peru, was published recently in the Journal of Tropical Ecology.

The footage raises the curtain on “a largely unseen world,” says Wilderson Medina, a Colombia-based researcher for the nonprofit Saving Nature, who was not involved in the work. “Because it’s very difficult to study, we don’t know much about life within the rainforest canopy; at night, it’s even more mysterious.” 

And tracking data-deficient species is especially important, says Duke University ecologist Stuart Pimm, who was not involved in the research. “Scientists set conservation priorities based on how endangered species are,” he says. Without that information, many species get neglected. “Almost certainly, the fact that they’re data-deficient means they’re very rare and may be in deep trouble already.”

Peering into hidden worlds

After her three-hour observation shift ends, Hughes checks her climbing harness, then rappels down the tree in darkness, clutching a rope in her hands. All around her, insects are buzzing loudly, and the air smells sweetly of flowers that open overnight for nocturnal pollinators. As she goes to sleep in a hammock at base camp, her research partner and husband, ecologist Trevor Hughes, ascends the tree for his three-hour shift. 

“This is the first time that we are actually able to see and follow the behavior of these animals in naturalistic conditions,” not just in zoos, says Dionisios Youlatos, an ecologist at Aristotle University of Thessaloniki in Greece, who was not involved in the research. “These are fabulous, amazing videos—you can trace what the animals are doing, how they do it, and follow them for 15 minutes or more.”

Youlatos, who studies how mammals evolved to live in trees, is especially interested in the Andean porcupine’s prehensile tail, which curls under branches to grasp them, as opposed to over the branch, like a monkey. “This allows them to move in a highly distinctive way,” he says, noting that part of the tail is furless for a better grip. “We have this idea that primates are the acrobats of tree life, but that’s not quite complete. Other animals like these small porcupines are also very, very agile, very fluid in what they do.” 

On several nights, Hughes watches from her canopy perch as night monkeys look for a snack. These charismatic 2-pound monkeys with huge eyes have been filmed before in their tree-cavity nests, but canopy antics have been difficult to trace. 

Previously, scientists thought night monkeys were mostly fruit eaters. But on several occasions, Hughes recorded as they slowed down, sniffed around, rose up on their hind legs on branches, then reached out quickly with both front paws to grab something: a juicy bug. “And then they stuffed it in their mouths,” Hughes says.

It’s little wonder that scientists have had trouble in the past knowing exactly what these little monkeys eat. But understanding their diet is essential to knowing what resources should be protected. Small nocturnal animals in the canopy are among the most elusive critters to track, says Medina. Two main obstacles are darkness and thick branches and leaves. “In some ways, the rainforest canopy at night is as inaccessible as the deep oceans,” Medina adds.

A new way of seeing 

Until recently, most surveys of tree-living nocturnal animals were conducted from the ground, looking up. A researcher would walk along a set path shining a flashlight into the branches and looking for the reflection of light on an animal’s eyes. Most animals would freeze and scamper away, making natural behavior elusive. 

In recent years, a combination of new approaches using heat-detecting technology has helped reveal hidden life in the rainforest canopy. Each method has strengths and limitations.

Mounting small motion-activated cameras in trees—some of which can film both daytime and nighttime footage—has greatly expanded scientists’ view of arboreal life, says Youlatos. After the initial setup, these devices, which may use infrared or thermal technology, require less time and effort to maintain than traditional ground-based surveys. But the limitation is that the motion-activated cameras don’t move around to follow the animals, and so you usually only capture a few seconds of motion in frame, says Youlatos.

More scientists in the tropics have begun to fly heat-sensing drones, which can detect large-bodied rainforest animals like sloths or orangutans from above. “Thermal drones can cover large distances and find many animals remarkably quickly,” says Hugo Fernandes-Ferreira, a zoologist at the State University of Ceará in Brazil. But they can’t peer inside the canopy to find tiny animals.  “The dense canopy cover can block the heat signature,” he explains.

What thermal binoculars add is the ability to observe small nocturnal animals up close and going about their daily lives for longer periods of time. “We can find the animals, but most of the time, they don’t react to us in any way,” says Hughes. “They get on with their everyday life. We can just watch their behavior.” 

A kaleidoscope of new techniques 

More than half of species currently labeled as data-deficient may already be threatened with extinction, according to a 2022 report in the journal Current Biology.

“These species are hard to see—they are often nocturnal or have small ranges or remote locations,” says Francesca Verones, an industrial ecologist at the Norwegian University of Science and Technology. “But the absence of data doesn’t mean there’s no risk.”

If anything, she believes the scarcity of sightings suggests the risk is already high. “The data-deficient species are the ones we should be worried about,” she says.

Collecting more information is a necessary first step to getting governments and conservation programs to pay attention, says Pimm: “If [animals] don’t have an endangered label stuck on them, people can lose interest.”

The rainforest canopy at night is one of the planet’s hidden places, but it’s not the only one. Scientists are also using new methods and technologies to explore other once-mysterious realms, including high mountains and the deep sea. 

More than 10 percent of amphibians are considered data deficient. In the Pyrenees mountains, Rafael Márquez, an ecologist at Spain’s National Museum of Natural Sciences, is using sound recordings, called “bioacoustics,” to track rarely seen frogs. “This works best for noisy animals,” he says. “For most frog and toad species, the males emit a very characteristic advertising call.”

At depths up to 6 miles, or 10,000 meters, beneath the ocean’s surface, Xiaotong Peng, a researcher at the Institute of Deep-sea Science and Engineering in Sanya, China, leads missions to study deep-sea life, including sightings of data-deficient upside-down anglerfish, using the institute’s deep-diving manned submersible.  “Every dive is a discovery,” he says.

All these approaches can hopefully together give scientists a better view of elusive biodiversity, and perhaps some hints about how to protect it, says Hughes. 

In the Panamanian rainforest canopy, “we know that a lot of these small animals are eating fruits, dispersing seeds, pollinating flowers—they’re important to the whole forest,” she notes. “We want to understand animal behavior to understand how things work together. Nothing is in isolation.”

Such detailed information is essential to identify the precise habitats animals need to survive, says Pimm. Some species may need old tree cavities for nesting or a nearby wetland or marsh, or they might need certain plants that attract insects they eat. “Not all forests—or parts of a forests—are the same,” he says.

For Hughes, every night in the canopy is different. “The excitement of not knowing exactly what I’ll see keeps me alert and awake” in the wee hours, she says. “It’s part of the magic.”