Why Do Monkeys Have Red Bottoms?

February 15, 2024

Monkeys with red bottoms, such as baboons, mandrills, and many species of macaques, display this feature to communicate important information about their fertility, social ranking in their troop, and sexual readiness. These primates spend much of their time sitting, and their hairless behinds are thickened with ischial callouses — thickened areas of skin that do not have nerve endings. These are known as “bottom pads” and serve as cushions to support their weight when they sit.

Female monkeys and baboons often have a reddened enlarged buttock, or sexual swelling, when they are at the peak of their menstrual cycle. This enables males to identify which females are biologically fertile and ready to mate.

A similar pattern is observed in the females of the rhesus monkey (Mavava mulatta), which have red rumps that enlarge during times of high ovulation. This is a clear signal of sexual readiness, and the males are highly attracted to females with bright red bottoms.

Among the other monkeys with red buttocks are the Japanese macaques, or snow monkeys (Macaca fuscata). According to an Okinawa folk story, the god turned the local rich man into a monkey because he refused to help a poor traveler. As a punishment, the monkey changed the rich man’s buttocks into a beautiful red color.

Monkeys with red bottoms play vital roles in the ecosystems where they live. Their consumption of fruits promotes fruit dispersal, and they contribute to the balance of the local plant communities. They are also known to raid crops, which can cause conflicts with humans. This is why it is important to protect their habitats and understand how these animals can coexist with humans.


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