Monkeys with red butts include baboons, mandrills, rhesus macaques, Japanese macaques, and Celebes crested macaques. Their rumps can look red, pink, blue, or purple for three different reasons: permanent hairless sitting pads, temporary hormone-linked swelling in cycling females, and longer-lasting skin coloration used in social or sexual signaling. A red rump does not automatically mean the animal is female, fertile, or ready to mate.
“Red butt monkey” is a useful search phrase, not a scientific group. The species below are all Old World monkeys, but the anatomy and meaning of their color differ. That distinction matters because permanent sitting pads are often mistaken for reproductive swelling, while a colorful male mandrill’s rear communicates something different from a swollen female baboon’s.
Key takeaways
- Many Old World monkeys have ischial callosities: tough, hairless pads over the sitting bones.
- In some species, tissue around a cycling female’s genitals temporarily swells and becomes pinker or redder as hormone levels change.
- Sexual swelling is usually a probabilistic fertility signal, not an exact ovulation clock.
- Adult male mandrills can have vivid red, pink, blue, and purple skin linked to sex, maturity, and social status.
- Chimpanzees and bonobos can also have sexual swellings, but they are apes, not monkeys.
Why do some monkeys have red butts?
There is no single explanation. What people call a “red butt” may be one feature or a combination of three.
1. Permanent sitting pads
Baboons, macaques, mandrills, and many other Old World monkeys have ischial callosities. These are thickened, hairless pads over the lower pelvis. They provide a stable surface for sitting on branches, rocks, or the ground. Because the skin is bare and can be pink, red, gray, or dark, the pads are much more visible than the same area on a furry animal.
The callosities are normal anatomy. They are not wounds, and they do not appear only during mating. Their size, shape, and color vary by species, sex, age, and individual.
2. Temporary sexual swelling
Females of some primate species develop temporary swelling in the anogenital tissue during the ovarian cycle. Hormonal changes increase fluid in the tissue and can make the area larger, smoother, and more intensely pink or red. The permanent sitting pads remain present beside or within the visibly swollen area.
Research on baboons and macaques shows that swelling can contain information about reproductive timing, but its reliability differs among species and individuals. In wild crested macaques, for example, swelling was largest around ovulation and larger in conceptive cycles, yet the researchers still described it as a graded, probabilistic signal rather than a precise announcement of fertility.
3. Longer-lasting ornamental coloration
Some red or multicolored skin is a sexual ornament rather than a short-lived swelling. Adult male mandrills are the clearest example. Their facial, genital, and rump colors become much more vivid than those of females and juveniles. A study of male mandrills linked the intensity of red coloration with dominance status and other reproductive traits.
Five monkeys with red or pink rumps
| Species or group | What the rear looks like | Main explanation | Native range | IUCN category |
|---|---|---|---|---|
| Hamadryas baboon and other baboons Papio species | Pink or red hairless pads; cycling females may develop larger swelling | Permanent callosities plus, in females, temporary sexual swelling | Africa; hamadryas baboons also occur on the southwestern Arabian Peninsula | Hamadryas baboon: Least Concern |
| Mandrill Mandrillus sphinx | Red, pink, blue, and purple bare skin, especially vivid in adult males | Sexual ornament and status signal; females can also show sexual swelling | West-central Africa | Vulnerable |
| Rhesus macaque Macaca mulatta | Red skin on the face and parts of the hindquarters; intensity varies | Bare vascular skin; female facial color can track cycle timing, but hindquarter color is less reliable | South, Central, and East Asia | Least Concern |
| Japanese macaque Macaca fuscata | Pink-red face and bare posterior | Naturally vascular bare skin, with variation among individuals and seasons | Japan | Least Concern |
| Celebes crested macaque Macaca nigra | Dark body with pale sitting pads and conspicuous pink-red swelling in cycling females | Permanent callosities plus a strong temporary fertility signal | Northern Sulawesi, Indonesia | Critically Endangered |
Species profiles
Baboons: sitting pads plus temporary swelling
Baboons are Old World monkeys in the genus Papio. All have conspicuous ischial callosities, although the pads are not equally red in every species or individual. Females of several baboon species also develop cyclical sexual swelling around the anogenital region.
The largest swelling does not simply identify the “best” or most fertile female. A long-term study of wild baboons found persistent differences among females and showed that swelling size also varied with the number of cycles since pregnancy and ecological conditions. In other words, males may gain useful information from the signal, but size alone does not provide a complete reproductive profile.
Hamadryas baboons occur in dry, rocky areas of the Horn of Africa and the southwestern Arabian Peninsula. Their multilevel societies differ from the social systems of many savanna baboons, which is one reason it is risky to treat every baboon as behaviorally identical. For a broader taxonomy overview, see these types of monkeys.
Mandrills: a multicolored status signal
The mandrill is an Old World monkey, but it is not a true baboon. Adult males are among the most visually distinctive primates, with red and blue facial skin and a bare posterior that may include red, pink, blue, and purple areas. Females and young mandrills are generally less vivid.
Male coloration is not merely decorative. Research has associated stronger red coloration with dominance, and color can change as a male gains or loses status. Females can also develop sexual swelling, so a mandrill’s colorful rear may combine relatively persistent ornamentation with temporary reproductive changes.
Mandrills live primarily in tropical and secondary forests in Cameroon, Equatorial Guinea, Gabon, and the Republic of the Congo. They eat fruit, seeds, fungi, roots, insects, and other small animals. The IUCN lists the species as Vulnerable, with habitat loss and hunting among the main concerns.
Rhesus macaques: red skin that changes across the reproductive cycle
Rhesus macaques are widespread and highly adaptable. Both sexes can show red skin, although the pattern and intensity differ. Adult females do not develop the large sexual swellings seen in baboons or crested macaques. In a study of free-ranging females, facial and hindquarter color varied across the ovarian cycle, but only facial redness reliably tracked the fertile phase. Hindquarter redness did not show the same pattern.
Rhesus macaques use many signals at once, including behavior, scent, vocalizations, proximity, and skin color. Their social rank and the seasonal timing of breeding also influence mating interactions. This is another reason to avoid reducing the entire system to a single visual cue.
Japanese macaques: pink-red skin and cold-climate adaptations
Japanese macaques, often called snow monkeys, have pink to red bare skin on the face and posterior. Their thick winter coat is the more important cold-climate adaptation. The red skin is not caused by snow or hot water.
A 2019 study of captive females found that facial and hindquarter coloration did not accurately indicate the timing of the fertile phase. Instead, color differences appeared to carry information about factors such as cycle history, rank, or body condition. This is another example of why “red means fertile” is too simple.
Some Japanese macaques at Jigokudani use hot springs in winter. A study of adult females found that bathing served a thermoregulatory function and was associated with lower glucocorticoid metabolite concentrations. This behavior is specific to certain troops and should not be presented as something every Japanese macaque does.
The species occupies subtropical, temperate, and cool mountain forests in Japan. Its range shows how flexible macaques can be across different ecosystems.
Celebes crested macaques: dramatic female swelling
The Celebes crested macaque, also called the crested black macaque, has black fur, a prominent crest, and pale ischial callosities. Cycling females can develop a large, conspicuous pink-red sexual swelling that contrasts sharply with the dark coat.
Field research found that swelling size and female receptive behavior were strongest around ovulation, and that males timed mating effort accordingly. The study still characterized the signals as probabilistic. A large swelling raises the likelihood that a female is near her fertile phase; it does not make conception certain.
This species is restricted to northern Sulawesi and nearby islands. It is Critically Endangered, making it the most threatened species in this comparison.
Does a red or swollen rump mean a female is ovulating?
Not necessarily. In some baboons and macaques, greater swelling or darker coloration can indicate that ovulation is more likely to be near. The relationship is species-specific, and even within one species it can vary among females, cycles, and environmental conditions.
Researchers describe many of these traits as graded signals. They provide partial information rather than a yes-or-no answer. Males can combine the appearance of the swelling with female behavior, scent, previous interactions, and the timing of the cycle. That combination may explain why male mating behavior can track fertile periods more closely than swelling size alone would predict.
The word “heat” is often used informally, but “cycling,” “sexually receptive,” or “near the fertile phase” is usually more precise for these primates.
Are baboon bottoms sore?
Healthy ischial callosities are not injuries. They are normal, thickened areas of skin adapted for sitting. A sexual swelling can look uncomfortable to human observers, but it is a normal temporary change in healthy cycling females.
That does not mean every red patch is harmless. Cuts, infections, parasites, inflammation, or trauma can affect any animal. A visibly injured captive primate needs veterinary assessment, while wild animals should be observed from a safe distance and never handled or fed.
Habitats, diet, and daily life
Monkeys with red or pink rumps do not form one ecological group. Baboons often use savannas, scrub, cliffs, and open woodland. Mandrills and Celebes crested macaques depend heavily on tropical forest. Japanese macaques occupy habitats from warm southern forests to snowy mountain regions, while rhesus macaques can live in forests, farmland, towns, and temple complexes.
Most of the species discussed here are flexible omnivores. Depending on the species and season, they may eat fruit, seeds, leaves, roots, fungi, insects, eggs, or small vertebrates. Their mobility and varied diets help some populations adjust to changing food supplies, but adaptation to human-dominated areas can also lead to crop raiding, feeding by visitors, traffic injuries, and conflict.
For more context on the environments that shape these behaviors, compare common primate habitats.
Conservation: color says little about extinction risk
A striking red rump does not predict whether a species is common or endangered. The rhesus macaque, Japanese macaque, and hamadryas baboon are currently listed as Least Concern, although local populations can still face pressure. The mandrill is Vulnerable. The Celebes crested macaque is Critically Endangered. These categories should be checked against the IUCN Red List whenever the article is updated.
The most important threats differ by place, but they include forest clearance, fragmentation, hunting, capture for trade, road development, and conflict around crops or food waste. Conservation therefore has to focus on the species and landscape, not on the visual trait. See practical habitat-loss solutions and an explanation of how conservation categories differ.
Conservation categories can change after reassessment. Check the IUCN Red List before quoting a status in future updates, and avoid unsupported global population totals when no defensible estimate is available.
Animals often confused with red-butt monkeys
- Chimpanzees and bonobos: females can develop sexual swellings, but both animals are great apes rather than monkeys.
- Red colobus monkeys: “red” usually describes the coat, not a red rump or sexual swelling.
- Lesulas: this African monkey is better known for blue bare skin in the perineal region, not a red butt.
- Geladas: these monkeys have a conspicuous red chest patch; the signature color is not on the rump.
Frequently asked questions
Why do baboons have red butts?
Baboons have permanent hairless sitting pads called ischial callosities. In cycling females, nearby anogenital tissue can also swell and become redder as hormone levels change. The visible rear is therefore a combination of normal anatomy and, at some times, reproductive signaling.
Which monkey has the brightest red butt?
There is no objective winner because color varies by sex, age, reproductive state, lighting, and individual. Adult male mandrills have the most elaborate multicolored posterior, while cycling female Celebes crested macaques and some baboons can develop especially conspicuous pink-red swellings.
Do male and female monkeys both have red rumps?
Yes, in some species. Male mandrills and rhesus macaques can show strong red coloration, while temporary sexual swelling is a female trait. Both sexes of many Old World monkeys have permanent ischial callosities, although their color differs.
Does a swollen red rump mean a monkey is ovulating?
It can indicate that ovulation is more likely to be near in some species, but it is not an exact test. Swelling size and color are graded signals, and males also use behavior, scent, social context, and previous cycle information.
Are red monkey bottoms painful?
Normal sitting pads are not injuries, and cyclical swelling is a normal physiological change. Cuts, infection, parasites, or trauma are different and may require veterinary care in captive animals.
Are chimpanzees monkeys with red butts?
No. Chimpanzees are great apes. Some female chimpanzees develop prominent sexual swellings, which can look similar to the swelling seen in certain monkeys, but their classification is different.
The bottom line
The phrase “monkeys with red butts” covers several distinct biological features. Baboons and macaques may combine permanent sitting pads with temporary female swelling. Mandrills add a striking, longer-lasting color signal that is especially strong in adult males. The safest interpretation is therefore species-specific: identify the monkey first, then ask whether the visible color comes from anatomy, reproductive state, social status, or a combination of all three.