An Exploration into the Studies of Spider Monkey Poop
Its 5am and the forest is just waking up. Under the canopy it’s still pitch black, but the rustles of the daytime animals emerging from their dens and stretching their legs is audible alongside the singular call of the howler monkey telling the rest of the forest it’s time to get up. Above me I can hear the spider monkeys talking to each other and affirming group cohesion, much like how we say, “good morning.” Suddenly, I feel a warm, light drizzle on my head, followed by the sound of something dense splattering on the ground not too far from me. I smile.
Spider monkeys are an incredibly important part of the forest ecosystem on the Osa Peninsula. They’re known as primary seed dispersers, which means the seeds they digest from eating fruit gets spread around the forest as they poop it out. One study found that seeds were dispersed from 83 meters to 1741 meters, but most figures were well over 100 meters – and they considered their study an underestimate.1
This is why the spider monkey is called an ecosystem engineer, and why they are important for biologists to study. As ecosystem engineers, these primates have the ability to help rebuild damaged and cleared forests which is important in the larger goal of keeping our rainforests healthy.
There is one important aspect of spider monkey behavior that is rather unusual: they poop after they wake up and before they go to bed, but will rarely poop in random spots through the forest. This creates these massive buildups of poop under specific trees around the forest, which are called latrines.
My work in Costa Rica centered around these latrines, and the ecosystem they create. That’s right – these piles of poo create entire ecosystems. When the poop falls, a whole host of insects are attracted to it: dung beetles, all types of ants, and flies. Then, their predators—which include anoles, all types of frogs, including poison dart frogs, and ant birds—are attracted to the latrines. Not only are predatory animals attracted to these sites, but seed eaters are attracted as well. We were able to collect camera trap footage of a whole host of seed predators and secondary seed dispersers, including the agouti, all types of small mice and rats, and pacas. These rodents exhibit a behavior called seed caching, where they stuff as many seeds as they can into their cheeks and bury them somewhere else, often forgetting where. The latrines we were studying ranged in size from 1 meter across, to the entire edge of a stream bank—about 17 meters!
These latrines are where I spent most of my time in the forest. A co-worker of mine on multiple occasions had spotted the green and black poison dart frog gathering in groups of four or five at the latrines. This is incredible because these frogs are aggressive and territorial and will attack another frog for entering the territory. My job was to figure out why they were tolerating each other and what they were doing at the latrines.
The set up was simple: create an ethogram, sit 5 meters from the latrine with a camera and binoculars and wait.
For twenty days I spent five hours in the morning and three and a half hours in the afternoon sitting at these latrines doing observations. That’s a combined 170 hours of time watching these latrines.
I saw no poison dart frogs.
This time spent alone in the forest allowed me to do some quiet meditation and reflection on what the hell I was doing spending all my time sitting in the middle of the rainforest staring at piles of poo.
And every time a troop of monkeys would swing by, or a tamandua would plod along quietly near me, or a swarm of army ants would cause me to run head over heels from where I was sitting, I would be reminded.
- Arroyo-Rodriguez, V. (2017). Parent-parent and parent-offspring distances in Spondias radlkoferi seeds suggest long-distance pollen and seed dispersal: Evidence from latrines of the spider monkey. Journal of Tropical Ecology. Retrieved from: https://doi.org/10.1017/S02664674170000