The four species of primates found at Piro

Four species of primates can be seen at Piro Biological Station in Costa Rica. Squirrel monkeys (Saimiri oerstedii oerstedii), spider monkeys (Ateles geoffroyi), white-faced capuchins (Cebus capucinus), and howler monkeys (Alouatta palliata) are all monitored by the station with a focus on spider monkeys as indicators of overall forest health.  White-faced capuchins and mantled howler monkeys are both classified by the International Union for Conservation of Nature and Natural Resources as of least concern. Population trends for both of these species are unknown. Spider monkeys are classified as endangered, with population numbers decreasing and squirrel monkeys are currently classified as vulnerable with their numbers decreasing as well.

White-faced capuchin feeding

How do these four species exist in the same forest without conflict? Well, sometimes there is conflict, but these species differ in some ways. For example their diet and use of the forest is not identical, allowing each species to live together.

Howler monkeys predominantly consume leaves. They even regularly include mature leaves as a part of their diet, which is uncommon due to the high fiber content of mature leaves and relatively low abundance of readily accessible calories. Leaves aren't generally a desirable food item in tropical forests. Just think about fighting over lettuce: not a food item you'd fight over at the grocery store for. That said, you don't see howler monkeys fighting over leaves.

Spider monkeys specialize in the upper parts of the forest, including emergent trees and the upper canopy. They usually travel and forage high in the trees. Spider monkeys are frugivorous, preferring to consume ripe fruits if possible. Over 80% of their diet is composed of fruits. Spider monkeys consume fruit in the emergent level of the forest, where other primates may rarely visit, if ever. Ripe fruits are a desirable food item (I'm guessing you're likely to fight over a juicy peach than a piece of spinach), but spider monkeys are relatively large primates and, from what I saw, they typically dominate the other primate groups they encounter. Spider monkeys can also consume non-fruit items when needed/available, such as immature leaves, flowers, seeds, and even small insects.

Squirrel monkeys are also frugivorous but insects also compose a decent portion of their diet. These monkeys can use all levels of the forest but are mainly found in the lower canopy and understory, thus not overlapping with spider monkeys. They also seem to prefer secondary forest and river edge forests. When fruit is less abundant during the dry season, they increasingly depend on insects and other animal prey.

Squirrel monkey

Finally, capuchins occur in many types of forests (mangrove, dry deciduous, humid subtropical forests along with forests that have been degraded). Like squirrel monkeys, they can also be considered frugivores and insectivores. Their diverse diet includes fruits, seeds, flowers, frogs, and even small mammals. These intelligent monkeys, arguably the most intelligent monkey of Central and South America, are extractive foragers, meaning they can manipulate their environment to obtain foods that are embedded, sometimes using tools to obtain these food items. Examples of capuchin extractive foraging include pounding seed pods against the ground to open them, using sticks to probe for insects, and using specifically shaped rocks to crack open palm nuts.

How these four species of primates interact is not entirely understood. There is still much to be learned about interspecific competition, or competition between different species for the same resources, in Costa Rican primates.

To read more about these primates at Piro click here.