The owl monkey, or night monkey as it’s also called, is the only nocturnal primate species in the world. They hail from Central and South America, inhabiting either the tropical rainforests or the lowland forests of the region. There are 10 species of Owl Monkeys, and they are split into two groups.

According to the Wisconsin National Primate Research Center, one of the groups is known as the gray-necked, which are found north of the Amazon River. The other is the red-necked, and they are found south of the Amazon.

Owl Monkeys weigh around 2.2 pounds. Their bodies are covered in thick, gray fur. Depending on the species, they may have orange fur on their chests and bellies.

Their most notable feature has to be their big, round eyes, which are perfect for seeing in low light. Compared to other monkey species that are active during the day, the lens of the owl monkey’s eyes is more spherical.

Usually, owl monkeys live in pairs or small groups. A biological anthropologist from Yale University named Eduardo Fernandez-Duque stated that pairs of male and female owl monkeys form strong bonds with each other. They are genetically monogamous and mate for life.

“Owl monkeys are one of the few mammals where we have absolutely no evidence of unfaithfulness; there’s not a single genetic data point that suggests that males and females in pair relationships—who sleep together, feed together, move together—are not exclusively mating with each other,” Fernandez-Duque said.

Furthermore, male owl monkeys make some of the world’s finest fathers. They are heavily involved in raising and protecting their offspring. Research shows that the males groom, play, share food, and carry infants more often than the mothers.

The nocturnal creatures enjoy a diet of fruit, seeds, flowers, leaves, and insects. On occasion, they have been known to eat bird eggs and small birds. They also have a wide range of vocal sounds.

Their “loud, low-frequency” calls sound like an owl’s hoot. As for their lifespan, they live for about 20 years in captivity. One monkey in the wild was observed to be 11 years old.

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Not only are owl monkeys the best dads around, but they also help scientists fight disease. Owl monkeys have been used for vaccine research for malaria. They are ideal animal models because they are also vulnerable to the parasite that causes the disease in humans.

However, the process of capturing the monkeys for study can destroy their nests, which can harm their populations.

“After subjecting them to research procedures, the monkeys are released back into the wild without follow-up, which is possibly causing the displacement or hybridization of resident populations as well as risking zoonotic transmission,” said Angela Maldonado, a primatologist and director of the organization Fundación Entropika.