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Camera traps in trees reveal a richness of species in Rwandan park

Angolan Black and White Colobus (Colobus angolensis)

  • Camera traps set high up in trees in Rwanda’s Nyungwe National Park captured 35 different mammal species over a 30-day period, including a rare Central African oyan (Poiana richardsonii), a small catlike mammal that has not previously been seen in the park.
  • Arboreal camera traps are a viable method for conducting mammal surveys, especially when partnered with ground cameras.
  • Understanding what animals are present in an area is a first step toward protecting them.

Sneaking up on animals can be tough. That’s why wildlife researchers often turn to motion-sensing cameras, also known as camera traps, to study animals in the wild. However, most of these camera traps are positioned at or near ground level, leaving a diverse world of animals unexamined: those that dwell in the trees above.

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A blue monkey (Cercopithecus mitus) photographed by an arboreal camera trap. Photo courtesy of WCS Rwanda.

In the montane tropical forest of Nyungwe National Park, Rwanda, a team of researchers climbed 10 meters (30 feet) up into the trees to rig arboreal camera traps. They also placed a camera at the base of each tree. The 108 cameras captured more than 27,000 photos of wildlife over a 30-day period, according to a study published in the journal Animal Conservation conducted in collaboration with WCS Rwanda, University of Florida, WWF, and Rice University.

Among the photos were 35 different mammal species, including six primate species and a rare Central African oyan (Poiana richardsonii), a small catlike mammal that was not previously seen in the park.

A Central African oyan (Poiana richardsonii) photographed by an arboreal camera trap. This was the first record of this species in Nyungwe National Park. Photo courtesy of WCS Rwanda.

Nyungwe National Park contains many globally threatened and endangered species and is a top priority site for biodiversity conservation. Knowing what animals are present in an area is an important first step toward taking measures to protect them.

“Because these cameras are working all day and night, they capture animals moving through the landscape that may have been missed by the human eye,” said Jennifer Moore, a postdoctoral researcher at the University of Florida and lead author of the new study. “Because of this, camera traps are more likely to document rare species of conservation concern.”

The L’hoest’s Monkey (Cercopithecus lhoesti), photographed here by camera trap, is listed as vulnerable on the IUCN Red List. Photo courtesy of WCS Rwanda.

Moore wondered if setting cameras traps in trees might give a more complete picture of mammal species richness, the measure of how many different species are in an area. She was also curious how camera trapping compared to the traditional method of mammal surveying, in which researchers walk along straight lines, or transects, and take note of any wildlife they encounter.

“Species richness tells us about the health of an ecosystem. A higher species richness is generally a sign of a more stable ecosystem,” Moore said.

Researchers found that using all three methods — ground and arboreal cameras along with a line transect — gives the most complete picture of species richness. But if only two methods can be employed, either due to time, money, or other logistical constraints, using a combination of the ground and arboreal cameras gave higher and more precise estimates of the occurrence of animals in an area than any other combination of methods.

WCS field assistant, Janvier Twizeyimana, setting up a camera trap. Photo courtesy of Felix Mulindahabi/WCS Rwanda.

The camera trap method is not without its problems. One particular difficulty, said Moore, is that cameras can be triggered by any motion. Leaves blowing in the wind, a swaying branch — these are much more likely to occur in the trees, especially as you get higher into the canopy. Camera misfires result in a lot of empty photos to sort through. For instance, of the approximately 71,000 total photos captured for this study, only about a third were usable.

Despite some of the logistical and technical issues, Moore said she wants to get the message out that arboreal camera trapping is a viable method for species monitoring, especially for people who study primates. “We were able to capture photos of primates we knew were there but had never been able to photograph,” she said. These photos can be useful for understanding the behaviors of animals and their movements through the forest.

See related, Camera trapping in the trees, which shares solutions to challenges posed by arboreal camera trapping.

“A lot of people think that by now we know everything, but WCS in Nyungwe National Park started in the ’80s and we just found a new species in the park last year. So that just goes to show that even in places where researchers have been for decades, there is so much more to learn.”

A great blue turaco (Corythaeola cristata) photographed by an arboreal camera trap. Photo courtesy of WCS Rwanda.
A Lord Derby’s anomolure (Anomolurus derbianus) is a gliding squirrel that sleeps in the trees. Photo courtesy of WCS Rwanda.
A chimpanzee photographed by an arboreal camera trap. Photo courtesy of WCS Rwanda.
A potto (Perodicticus potto) also called a “softly-softly” is related to the lemur. Arboreal camera trap photo courtesy of WCS Rwanda.
Cassin’s hawk-eagle (Aquila africana) photographed by an arboreal camera trap. Photo courtesy of WCS Rwanda.
A serval (Leptailurus serval) photographed by a ground camera trap. Servals are solitary carnivores. Photo courtesy of WCS Rwanda.Photo courtesy of WCS Rwanda.
A Rwenzori turaco (Gallirex johnstoni). Arboreal camera trap photo courtesy of WCS Rwanda.
WCS field assistant, Janvier Twizeyimana , skillfully rigging a camera trap. Photo courtesy of Felix Mulindahabi/WCS Rwanda.

Citation: Moore, J. F., Pine, W. E., Mulindahabi, F., Niyigaba, P., Gatorano, G., Masozera, M. K., & Beaudrot, L. (2020). Comparison of species richness and detection between line transects, ground camera traps, and arboreal camera traps. Animal Conservation. doi:10.1111/acv.12569

Banner Image of a Angolan Black and White Colobus (Colobus angolensis). Arboreal camera trap photo courtesy of WCS Rwanda

Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough_

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