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In the Borneo canopy, life thrives in surprising ways, camera-trap study shows

Bornean gibbon

Northern gray gibbon (Hylobates funereus) displaying impressive balance at 36 meters. This is the first documented evidence of a gibbon walking upright along a branch. Image courtesy of Jessica Haysom/Durrell Institute of Conservation & Ecology (DICE), University of Kent

  • The first systematic camera-trapping survey of arboreal mammals in Southeast Asia reveals a diverse and distinct community; the researchers also recorded evidence of new behaviors and the first ever photograph of a rare flying rodent.
  • The team collected more than 8,000 photographs, cataloging 57 species in total, 30 of which were detected exclusively on ground cameras and 18 exclusively in the canopy.
  • Since few past studies have targeted arboreal mammals, scientists do not know how human disturbances such as logging may affect them.
  • The results demonstrate that surveying in the forest canopy is “crucial to our understanding of rainforest mammal communities,” say the study authors.

In her spare time as a research assistant in the forests of Sabah, Malaysian Borneo, Jessica Haysom turned to perusing mammal field guides. She found herself especially intrigued by the vast number of animals that live high in the Bornean forest canopy, about which next to nothing is known.

“The more I read, the more I realized that there was so much going on in the canopy which very few people were studying,” she said.

Now, she’s uncovering the secrets of that lofty realm. In a recent study in Frontiers in Forests and Global Change, Haysom and her team took cameras up into the trees, completing the first in-depth and systematic camera-trapping survey of an arboreal mammal community in Southeast Asia. The study reveals insights into Sabah’s tree-dwelling mammals, evidence of new behaviors, and the first ever photograph of a rare flying rodent.

“For a long time, we’ve only studied what’s on the ground because that’s really all that we’ve had access to,” Haysom, a doctoral student at the University of Kent, U.K., told Mongabay. “But the canopy is just as important and it would be foolish to ignore it because there’s so much that’s going on up there.”

Orangutan (Pongo pygmaeus) mother and baby photographed in the trees in a logged forest. The researchers observed orangutan family groups on several occasions during tree fruiting periods. Image courtesy of Jessica Haysom/Durrell Institute of Conservation & Ecology (DICE), University of Kent

Into the canopy

Arboreal, or tree-dwelling, mammals play a vital role in forests across the globe. In tropical rainforests, mammals ranging from tiny rodents to orangutans add to overall ecosystem resilience by both pollinating plants and dispersing seeds, thereby helping ecosystems regenerate and recover after disturbances.

Since few past studies have focused on arboreal mammals, scientists do not know how human disturbances such as logging affect them.

“[W]e may be missing declines in arboreal species and underestimating the true impact of logging,” the study authors write.

Recent advances in camera technology, climbing techniques and safety equipment have now brought the forest canopy more easily within researchers’ reach, allowing Haysom and her colleagues to deploy camera traps at 50 different locations between 2017 and 2019 in Sabah. The region is home to some of the world’s tallest tropical forests, with canopy heights typically ranging between 50 and 70 meters (160 and 230 feet), while emergent trees can reach 100 m (330 ft).

At each location, the researchers placed one camera in the canopy to capture arboreal species and one on the ground to record terrestrial species. Particularly interested in documenting whether mammal populations can recover after logging, the researchers positioned half of the cameras in Mount Louisa Forest Reserve, an area that experienced bouts of logging between 1978 and 2008, and the other half in undisturbed, unlogged forests in Maliau Basin Conservation Area.

Looking out from canopy over unlogged forest in Maliau Basin Conservation Area, Sabah. This photo was taken at 36 meters height. Image courtesy of Jessica Haysom
Jessica Haysom climbs a tree to position a camera, her colleague, Fredino John, is waiting above at 28 meters height. Image courtesy of Jamiluddin bin Jami

In all, the team collected more than 8,000 photographs, revealing a diverse community of mammals. They cataloged 57 species in total, 30 of which they detected exclusively on the ground and 18 exclusively in the canopy. Nine species, including Bornean orangutans (Pongo pygmaeus), binturongs or bearcats (Arctictis binturong), pig-tailed macaques (Macaca nemestrina) and yellow-throated martens (Martes flavigula) were found on both sets of cameras.

Haysom said she was surprised at how distinct the arboreal and terrestrial mammal communities appear to be.

“Most arboreal mammals are physiologically capable of descending to the ground, but it seems clear that most do not habitually do so,” she said. “This makes sampling in the canopy strata itself even more crucial to our understanding of rainforest mammal communities.”

The team found that arboreal camera traps are particularly effective at detecting gliding mammals, rodents and primates, including the maroon langur (Presbytis rubicunda), Sabah grizzled langur (Presbytis sabana), northern gray gibbon (Hylobates funereus), small-toothed palm civet (Arctogalidia trivirgata) and Temminck’s flying squirrel (Petinomys setosus).

And they got some surprises. The researchers took what they believe is the first ever photograph of a smoky flying squirrel (Pteromyscus pulverulentus). Rare even in primary forest, the smoky flying squirrel is listed as endangered on the IUCN Red List and the only species in its genus. They also caught a photograph of a mystery squirrel that doesn’t fit any known description for a Bornean species.

Potentially the first known photograph of a smoky flying squirrel (Pteromyscus pulverulentus). Image courtesy of Jessica Haysom/DICE, University of Kent

The team also caught unusual behavior, such as photographs of a northern gray gibbon walking upright along a branch. The camera traps further revealed that some species had a greater presence in the forest canopy than previously thought. The team was surprised to find plain treeshrews (Tupaia longipes), a species previously thought to dwell only on the ground, show up on arboreal cameras. Meanwhile, tufted ground squirrels (Rheithrosciurus macrotis) were detected scent-marking high in the trees. They also recorded canopy mating of small-toothed palm civets, a species thought patchily distributed based on ground observations, but commonly detected in both logged and unlogged forest on arboreal cameras.

“This reinforces that canopy-based sampling gives much clearer insights into the presence and behavior of arboreal species,” Haysom said.

However, canopy cameras in both logged and unlogged forest failed to detect wild cats, such as clouded leopard (Neofelis nebulosa) or marbled cat (Pardofelis marmorata). Researchers have long assumed such cats to be semi-arboreal.

According to Susan Cheyne, a primatologist at Oxford Brookes University, forest mammal monitoring has been overly focused on ground-level species due to the inaccessibility of arboreal species. In Borneo, this has likely led to information gaps regarding primates, civets and the arboreal behavior of cats.

“An understanding of the whole community of mammals in a forest is crucial to assess populations,” Cheyne, who was not involved in the new study, told Mongabay in an email. “So arboreal cameras are an important next step in camera trapping surveys.”

Tufted ground squirrels (Rheithrosciurus macrotis) were detected scent-marking high in the trees, this one was photographed during a lucky chance encounter in unlogged forest. Image courtesy of Jessica Haysom
Northern gray gibbon (Hylobates funereus) displaying impressive balance at 36 meters. Image courtesy of Jessica Haysom/DICE, University of Kent

Logged and unlogged

Haysom and her colleagues found high diversity in the arboreal mammal community in both logged and unlogged forests. In contrast, they found lower diversity among ground-level mammals in the logged forest compared to unlogged forest. These results contradict previous research in Borneo that suggested that ground-level mammal diversity can recover within a few decades after the cessation of logging. The researchers attributed this to animals descending from the canopy to ground level after logging, thereby artificially inflating species numbers.

The diverse arboreal community in the logged forest came as a surprise, Haysom said. It could be due to the fact that the logged forest in Mount Louisa Forest Reserve has been protected for at least a decade, experiences low hunting levels, and is of relatively high quality.

“It is possible that there is a threshold of disturbance beyond which most arboreal species cannot persist, and that this threshold had not been met in our study system,” the authors write in their study.

Nonetheless, the results indicate that even logged forest is useful for arboreal mammals.

“This is positive, because it shows that we still have room to conserve something that is there, rather than trying to repair something which is broken,” Haysom said.

The camera traps reliably detected fast-moving and strictly arboreal species. Gibbons, for instance, were detected frequently and across a wide range of locations, although they should be difficult to photograph because of their mode of traveling: hand over hand through branches. Furthermore, scientists also frequently detected nocturnal gliding species, such as flying squirrels and Sunda flying lemurs (Galeopterus variegatus).

For Haysom, climbing into the canopy to set up and retrieve cameras really brought home the vastness and interconnectedness of the forest canopy.

“From the ground, we look up and generally see a tangled ceiling of green — we know there is a lot up there, but we cannot see much of it or how far it extends. Once you’re in the canopy, it really becomes apparent that you are in a huge and intricate 3D space extending above, below, and all around.”

Camera traps no longer simply tell us what species are around; as technology continues to develop, the scope of studies also expands. Next, Haysom is going to employ camera trap data to calculate species activity patterns, occupancy models and the influence of vegetation structure on the probability of detecting species.

“There’s just so much potential for these more intricate studies as well as these bigger landscapes studies,” she said.

Looking down from an emergent tree at 52 meters. Research assistant, Almius Jupri, descends towards the unbroken mid-canopy. Image courtesy of Jessica Haysom
The researchers recorded canopy mating of small-toothed palm civets (Arctogalidia trivirgata), a species almost never recorded at ground level, but which camera-traps revealed to be common in the canopy. Image courtesy of Jessica Haysom/DICE, University of Kent

Citation:

Haysom, J. K., Deere, N. J., Wearn, O. R., Mahyudin, A., Jami, J. B., Reynolds, G., & Struebig, M. J. (2021). Life in the canopy: Using camera-traps to inventory arboreal rainforest mammals in Borneo. Frontiers in Forests and Global Change, 4. doi:10.3389/ffgc.2021.673071

Editor’s note: This story was supported by XPRIZE Rainforest as part of their five-year competition to enhance understanding of the rainforest ecosystem. In respect to Mongabay’s policy on editorial independence, XPRIZE Rainforest does not have any right to assign, review, or edit any content published with their support.

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