Filippo Aureli and Mónica Maravert Solano
Do you remember that a couple of years ago the ConMonoMaya team installed camera traps (also called trail cameras) on trees at LAT (Los Arboles Tulum)? Camera traps are used to take images of wildlife without the possible interference of the researcher presence. This method is especially useful to document the presence of species that are particularly shy and keep away from people. In addition, camera traps can monitor the area in front of them 24 hours a day, like surveillance cameras, providing information about animals during the day as well as at night. When camera traps are installed on trees, they are called arboreal camera traps. They are useful to document the presence and behavior of arboreal species, which is difficult to document with camera traps installed at ground level. Therefore, arboreal camera trapping gives us a view of what happens where we cannot usually see like tree canopies. In this article we tell you what we learned from arboreal camera trapping at LAT based on a presentation we have recently given.
On November 27, 2024 we gave the presentation “Monitoreo con cámaras trampa arbóreas para la conservación de primates” (Arboreal camera trap monitoring for primate conservation) in the Symposium “Avances en el uso e implementación de tecnologías emergentes para el monitoreo de primates” (Advances in the use and implementation of emerging technologies for primate monitoring) at the 5th congress of the Latin American Society of Primatology that was held in Pereira, Colombia. The symposium was organized by Denise Spaan, Eduardo José Pinel Ramos, Victor Beltrán Francés and Filippo Aureli with the aim of reviewing current knowledge on technologies, such as camera traps, drones and autonomous acoustic recorders, to monitor primate populations and exchange experiences on successes and failures, as well as challenges and solutions with colleagues from all over Latin America.
Our presentation was based on three camera trap studies that were conducted in Mexico and Colombia. Two of them were carried out by Dr. Sabine Cudney-Valenzuela (Figure 1): one during her PhD project at the UNAM collecting data in the Lacandona forest in Chiapas, and the other during her postdoc project at University of British Columbia, Canada, collecting data in the coffee-growing region of Colombia. Both studies took place in patches of forest surrounded by cattle pasture and croplands. Landscapes that differ largely from LAT.
The third study was the one we carried out at LAT. In December 2021, Dr. Sabine Cudney-Valenzuela was the invited expert at the fourth LAT scientific workshop. This workshop focused on the use and installation of arboreal camera tramps. During the workshop, Sabine taught several of our team members to climb trees, complementing the sessions that Hawthorne started earlier in the year. With Sabine’s expert guidance we installed 11 camera traps to monitor which species visit and use trees that are important in the spider monkey diet.
In 2022 we carried out a pilot study in LAT using the camera traps. Mónica Maravert Solano (Figure 2) and Bac Yaroslab Becerril Vargas climbed the trees every 1-2 months to change the memory cards and the batteries in each camera trap. They then reviewed all the images (photos and videos) to see which had animals and identify the species. As it is difficult to clear all the small branches and leaves in the camera´s view that could trigger the camera, when working with arboreal camera traps the memory cards are full of images triggered by movements of the vegetation due to the wind without any animals in them. Mónica and Bac needed to go through thousands of images to select those with animals. For example, while reviewing 1,619 images recorded on one tree they were able to find only 65 images with animals in them (only 4% of the total images recorded on the memory card). Still, all the effort of climbing up and down the trees and going through thousands of images was worth it as the images revealed many different species using the trees we selected for our pilot study.
The camera traps captured several images of spider monkeys (Figure 3), confirming that this technology is suitable to document spider monkey use of food trees. It is also possible that one camera trap captured an image of a howler monkey, but it is difficult to confirm it given that the photo shows only a hand or foot (Figure 4). We know that howler monkeys are heard and seen sometimes at LAT, but not during the study period.
In addition to spider monkeys, we were able to identify other seven mammal species in the images obtained from the camera traps: the Yucatan squirrel, the Deppe’s squirrel, the Northern tamandua (Figure 5), the white-nosed coati, the Virginia opossum, the kinkajou (Figure 6), and the Mexican hairy dwarf porcupine. We already knew these species occurred in LAT, but we were positively surprised to encounter an image of the cacomixtle (Figure 7), which is the first evidence of this species occurring in LAT.
We also found images of 19 bird species, including the ferruginous pygmy owl (Figure 8) and the great curassow (Figure 9).
As this was a pilot study testing the technology, we experimented with different types of batteries. Camera traps usually need several (4-8) AA batteries. Camera manufacturers recommend using alkaline batteries, which are not environmentally friendly. As batteries need to be changed every 1 – 2 months, a large-scale project will use hundreds of batteries. This amount of waste seems contradictory for a conservation project like ours. We therefore explored whether other types of batteries could work for camera traps. To our joy, we found out that all four alternative types of batteries we used worked well. Although the three types of rechargeable batteries worked well, they discharged to about half of their capacity in only 15 days. Lithium batteries lasted the entire study period and after a year still showed a 100% charge!!!!
Although it is challenging to climb trees and install camera traps on tree branches, our pilot study in LAT confirmed that the use of arboreal camera traps is an effective and noninvasive method to monitor nocturnal species (animals that are active at night) and cryptic species (animals that is difficult to distinguish from the background of its natural environment) at a large number of sites simultaneously, without the need of trapping or manipulating animals. Our study showed that it is also useful to monitor the use of food trees by spider monkeys and several other mammalian and bird species. When we did this study a couple of years ago, one of the challenges we encountered was the time-consuming review process of thousands of images captured by the camera traps looking for animals. Luckily now, this challenge can easily be solved through programs based on artificial intelligence that can be trained to go through all the captured images and identify those with only animals.
We believe our pilot study at LAT was successful as we obtained promising preliminary results about the species living in LAT and the use of alternative battery types, on which we or others can build to design future projects. Our symposium presentation of these results was well received and gave us the opportunity to build a network of users of similar technology to monitor wildlife with whom to exchange experiences to find solutions to common challenges, avoid others’ failures and increase success.