Monkeys with red bottoms are a fascinating primate phenomenon. This distinctive physical trait occurs in several monkey species, particularly those native to Africa and Asia. But why do some monkeys have bright red bottoms? And what purpose does this colorful rear end serve? Let’s take a closer look at the red-bottomed monkeys of the world.
What Causes Red Bottoms in Monkeys?
There are two primary reasons monkeys can develop red bottoms
Breeding Signals
In many monkey species, the bottoms of females turn red and swell when they are ovulating and ready to mate. This functions as a sexual signal, advertising the female’s fertility to potential mates. The swollen red rear is thought to attract male attention and indicate optimal timing for breeding.
The red bottoms reach peak swelling when females are most fertile, sometimes growing 4-6.5 inches in size. However, research suggests the degree of swelling may not directly correlate with increased reproductive success. Some females with less exaggerated swelling still successfully attract mates and produce offspring.
Ischial Callosities
Many monkeys also develop red patches on their bottoms due to ischial callosities. These thick, hairless calluses result from sitting directly on the bottom all day. The friction and pressure leds to increased blood flow and redness in this area Ischial callosities are present in both male and female monkeys
12 Monkeys Known for Their Red Bottoms
Here are 12 of the most prominent red-bottomed monkey species:
1. Hamadryas Baboon
Native to the Horn of Africa, these monkeys are nicknamed “sacred baboons.” Both males and females develop bright red bottoms.
2. Guinea Baboon
The smallest baboon species has red bottoms and genitalia when females ovulate. Males also greet each other with “peace signs.”
3. Japanese Macaque
These cold-loving monkeys feature vivid red faces and bottoms. They are known for bathing in Japanese hot springs.
4. Rhesus Macaque
Common across South and Southeast Asia, these monkeys thrive in urban areas near human populations.
5. Stump-Tailed Macaque
Males are distinguished by their large size and red faces and bottoms. Despite their imposing appearance, they are very peaceful.
6. Celebes Crested Macaque
Known for their punk-style black crest, these Indonesian monkeys develop red swollen bottoms when females are in heat.
7. Mandrill
Native to West Africa, Mandrills are among the largest monkeys, with blue and red coloring on their faces.
8. Drill
Similar in appearance to Mandrills, these monkeys also congregate in very large troops up to 200-300 individuals.
9. Olive Baboon
Widespread across Africa, these baboons get temporary red rumps during ovulation. Females also mate with multiple partners.
10. Moor Macaque
Endangered monkeys from Indonesia with bare red patches on their rumps from sitting and foraging habits.
11. Chacma Baboon
As the largest baboon species, these monkeys can grow over 50 inches long! They are found in southern Africa.
12. Bonnet Macaque
Native to India, these monkeys have fully red faces in addition to their red bottoms. They are very common in urban areas.
Conservation Status
Most red-bottomed monkey species are widespread and not considered endangered. However, some populations are declining due to habitat loss from human activities like logging, mining, and agriculture. The monkeys’ tendencies to raid crops also leads to conflict with farmers. Careful monitoring of at-risk species is needed to preserve these fascinating primates and their distinctive red rear ends well into the future.
Getting to the Bottom of Baboon Bottoms
I have received some interesting reactions when I tell new acquaintances that I study baboons. Recently, someone very enthusiastically asked, “Those are the animals with the HUGE pink butts, right?” They are indeed. And I’m actually quite intrigued by those “pink butts.”
A more technical term for this is “exaggerated sexual swellings.” Around the time of ovulation, females of some Old world monkey and ape species exhibit these swellings. Sexual swellings are not actually swollen butts. Rather, they are swellings of the perineal skin.
The existence of exaggerated sexual swellings is intriguing because they are costly to produce. When maximally swollen, female body weight increased by over 25% in red colobus monkeys (Colobus badius) (Struhsaker 1975). Such a large increase in weight on your backside must be uncomfortable and likely increases the energy costs of locomotion. To add to this, swollen females deal with increased parasites and cuts to the surface of the swelling (Hausfater 1975). Females are dealing with noticeable costs as a result of these sexual swellings. Thus, it is expected that swellings confer significant benefits. What could these benefits be?
Currently, the favored hypothesis regarding the function of exaggerated sexual swellings is the “graded-signal hypothesis” (Nunn 1999). This hypothesis focuses on variation within a female’s reproductive cycle and posits that exaggerated sexual swellings function to both confuse paternity and concentrate the probability of paternity in the highest quality male. Prior to this hypothesis, these two functions were proposed as opposing explanations. They do seem to be contradictory, right? But Nunn (1999) was able to incorporate both ideas into his graded-signal hypothesis.
So how can swellings both concentrate and confuse paternity? They can concentrate paternity in the highest quality male by inciting the most intense competition when the sexual swelling is at its maximum size (when the probability of ovulation is highest), and they can confuse paternity by exhibiting swellings for an extended period of time and mating promiscuously.
This is a remarkable strategy for females! By swelling outside the period of ovulation and mating promiscuously, they create paternity uncertainty. When there is even a slight chance that a male could be the father of an infant, it is unlikely that he would kill it (i.e. commit sexually selected infanticide). Now, these females may be mating promiscuously but at the time of ovulation, they can limit their mating to males of their choice! Thus, females with swellings can receive the benefits of mate choice and paternity uncertainty.
Another explanation for the function of exaggerated sexual swellings is the “reliable-indicator hypothesis.” This hypothesis examines variation across females and proposes that swelling size is an honest indicator of the female’s quality as a mate (Pagel 1994).
When we learn about sexual selection, we learn that females should be the more discriminating sex while males should compete for access to females and mate with as many females as possible. Working under this (simplified) framework, why would primate males be choosy about female quality? Pagel (1994) argued that mating can be costly for males, especially in multi-male mating systems in which males compete physically over females. This suggests that males are more selective due to the high mating costs associated with multi-male groups. As a result, it would benefit females to signal their high quality via a nice sexual swelling.
These two hypotheses are fundamentally different. The reliable-indicator hypothesis predicts female-female competition and honest signaling to males, whereas the graded-signal hypothesis predicts that females manipulate the information available to males. The graded-signal hypothesis has received substantial theoretical and empirical support. In contrast, the reliable indicator hypothesis has received less consistent support. However, I think the latter provides an interesting perspective and challenges traditional views.
Exaggerated sexual swellings are meant to draw attention to the females exhibiting them. And they do a great job of this! Well…at least humans are drawn to them — both the general public and scientists show an interest in these swellings. But nonhuman primate males seem to be quite interested in them as well! We don’t have all the answers yet though. A combination of theoretical modeling, comparative analyses, experimental studies, and observational studies are necessary to rigorously investigate the adaptive function of exaggerated sexual swellings.
Hausfater, G. 1975. Dominance and reproduction in baboons (Papio cynocephalus): a quantitative analysis. Contributions to Primatology, 7, 1-150.
Nunn, C. 1999. The Evolution of Exaggerated Sexual Swellings in Primates and the Graded-signal Hypothesis. Animal Behaviour, 58.2, 229-46.
Pagel, M. 1994. The Evolution of Conspicuous Oestrous Advertisement in Old World Monkeys. Animal Behaviour, 47.6, 1333-341.
Struhsaker, T. T. 1975. The Red Colobus Monkey. Chicago: Univer- sity of Chicago Press.
Association for Conservation of the Tropics
TIL: Why Do These Monkeys Have Big, Colorful Butts? | Today I Learned
FAQ
What monkeys have red bottoms?
Answer and Explanation: The baboon is a type of monkey that has a red bottom. This feature is quite important when it comes to mating.
Why do monkeys have red buttocks?
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These are essentially hardened pads of skin on the buttocks of certain primates, including baboons.
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In baboons, these callosities become more prominent and redder during ovulation, a time when females are most fertile.
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Sexual Signaling:The swelling and redness of the ischial callosities serve as a visual cue to males, indicating that a female is receptive to mating.
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Not all monkeys have them:Not all monkey species have these features. Ischial callosities are a characteristic of Old World monkeys, gibbons and some chimpanzees.
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Evolutionary AdaptationThe ischial callosities enable the monkeys to sleep sitting upright on thin branches, beyond reach of predators, without falling.
Is a baboon a monkey?
What are baboons? They are some of the world’s largest monkeys. There are five species of the baboon — olive, yellow, chacma, Guinea, and sacred — scattered across various habitat in Africa and Arabia. The olive baboon is the most extensively distributed of the baboon family.
Do female baboons have red bottoms?
Female baboons are known for their distinct red bottoms, known to attract potential mates. But according to a new study, there’s more to baboon courtship than these preposterous looking posteriors.
What monkeys have red butts?
Some of the most recognized monkeys with red butts include the following species. 1. Hamadryas Baboon Hamadryas Baboons (Papio hamadryas) are colorful and red-bottomed. Both males and females show bright red bottoms, despite having a different appearance. Smaller females are brown while males twice their size are silver.
What do monkeys with red bottoms look like?
Monkeys with red bottoms, also known as “red butt monkeys,” are characterized by their hairless bottoms, which range in color from red to dark red or pink-red. These distinctive animals are found in various regions across Africa and Asia.
What color are the hairless bottoms of ‘red butt monkeys’?
Monkeys with red bottoms, also known as “red butt monkeys,” are characterized by their hairless bottoms, which range in color from red to dark red or pink-red.
Why do female monkeys have red butts?
Female red butt monkeys display their swollen red butt bottoms as an indication of fertility, which attracts the attention of male counterparts for potential mating opportunities. As diverse and captivating creatures, monkeys with red butts garner significant interest from researchers and animal enthusiasts.
Why do red butt monkeys have swollen bottoms?
Red butt monkeys have swollen bottoms that serve as non-verbal cues for communicating with other members of their species. Female red butt monkeys display their swollen red butt bottoms as an indication of fertility, which attracts the attention of male counterparts for potential mating opportunities.
Are red-bottomed monkeys chimpanzees?
It is essential to distinguish these red-bottomed monkeys from other primates, such as chimpanzees, which are part of the Great Apes family and do not exhibit red-bottomed features. Monkeys with red butts are known for their distinctive red patches on their buttocks, which serve as a primary means of communication for mating purposes.