The world holds very few unexplored places between zero and six feet off the ground. If humans can walk right up to it and take a picture, we probably already have. But the tops of the trees, like the bottom of the ocean, are a different story.
“We know so much less about arboreal mammal activity than we do about terrestrial mammal activity,” says Tremaine Gregory, a research scientist at the Smithsonian Conservation Biology Institute. She thought camera-trapping, a common method for observing land animals, might also be useful for studying the ones hiding in the treetops. That’s why she hooked herself to a rope and started hoisting cameras into the towering Amazonian canopy.
Gregory is studying an area in Peru where a strip of rainforest was recently cleared to make way for a natural gas pipeline. Along part of this corridor, “natural bridges” were left in place: pairs of branches from trees on either side that reach across the open space and connect in the middle. While all the other trees and plants were chopped out of the pipeline’s way, 13 of these naturally occurring bridges were preserved along 5 kilometers of the corridor.
Along with one of her coauthors, Gregory ascended into the canopy and rigged cameras to 25 points along these bridges. On average the cameras were about 27 meters (almost 9 stories) high. The scientists also positioned camera traps on the ground below the trees for comparison.
Camera traps are made to snap a picture whenever something warmer or cooler than the background temperature moves in front of them. In theory that should mean most of the shots show animals. In reality, objects like waving leaves that are warmed by the sun can also trigger a picture.
This proved to be an especially big factor for camera traps in trees. The first check-in showed that the cameras’ memory cards were rapidly filling up with photos of foliage. So the scientists hauled pruning shears up to the canopy and cleared a small area around each lens, which helped somewhat. There were other difficulties with the cameras too: one was infested with insects, for example, and four were gnawed open by tree porcupines.
Thanks to wind, sun, leaves and bugs, almost 98% of the pictures taken over 6 months were the accidental kind. On the ground, where cameras couldn’t blow in the wind and vegetation had been cleared for the pipeline, accidental photos made up a mere 5.6%. But, Gregory explains, the added hassle in the trees was totally worth it.
Once researchers removed all the extras, they were left with more than 8,000 photos showing 22 mammal species, 20 birds, and 4 reptiles. They saw more animals at night than during the day. This was especially exciting, Gregory says, because a recent study on the ground had turned up very few primates—perhaps some of these primates were hiding out during the day, and not simply depleted by hunting.
The photos showed that animals didn’t change their behavior over time to avoid the cameras. They also revealed that animals are using the natural bridges often. Those using the bridges don’t like to cross on open ground—the 17 mammal species photographed on the ground had almost no overlap with those in the trees.
Arboreal camera traps spotted animals grooming, feeding, and carrying their babies. The let scientists see how groups of animals shifted over time and how their young developed. They even revealed when some animals got injuries like broken limbs and tails or missing eyes.
Gregory thinks camera trapping, which is inexpensive and non-invasive, should be a tool for research in the canopy as well as on the ground. Once you sift through the thousands of portraits of windblown leaves, she says—and maybe an insect infestation here or there—”I think the rewards of arboreal camera trapping are priceless.”
See some of those priceless photos above.
Images: Tree climbing by Farah Carrasco, Smithsonian Conservation Biology Institute. All others courtesy of the Smithsonian Conservation Biology Institute.
Gregory, T., Carrasco Rueda, F., Deichmann, J., Kolowski, J., & Alonso, A. (2014). Arboreal camera trapping: taking a proven method to new heights Methods in Ecology and Evolution, 5 (5), 443-451 DOI: 10.1111/2041-210X.12177