Why do Female Baboons have Swollen Bottoms? Why is a Baboon’s butt red?

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Why do female baboons have swollen bottoms?

Female baboons have red swollen bottoms in order to indicate that they are ready to mate and are ovulating or will be ovulating very soon. It indicates the timing during which the female is in her follicular phase and heat phase and is most fertile to perform sexual intercourse during that time period.

At every 34 to 37 days time period, the female baboons will start to have swollen bottoms. And during the normal non-ovulating times their bottoms shrink back to normal.

So, the next time you will see a female baboon with having a swollen bottom, which is actually the big-sized swollen butt, then always remember that it is a sign of their pronounced sexual swelling, sexual advertisement, and highly fertile phase.

It is when the ovulation time approaches, female baboons start to show an increased swollen bottom size of up to 7 inches (17.8 cm) than normal.

Some baboons can show an increased swelling size of about 10 cm only. That can be due to the direct correlation with their ovulation rate.

So, those that swell more result in a bigger rear butt display and so are able to attract more mates. And those that swell less are sometimes less attractive to males.

However, it is also to be noted that, not all big-bottomed females are always attractive to males, but in most instances they are.


Just like when a female has an infant or has just recently (a few months back) given birth to a baby, then she is less likely to mate with a male. So, such big-bottomed females if found are usually less attractive to males.

It is also to be noted that females with bigger backsides don’t necessarily make better mothers, as a recent study suggests.

Sexual Swelling in female Hamadryas Baboon (Source: Mamoritai, CC BY-SA 2.0, via Wikimedia Commons)

Why is a baboon’s butt red?

Red butt of Baboon is a result that is caused due to their butt being swelled with blood, water, and other body fluids, giving it a bright pink to red color in appearance. In fact, the baboon is a type of monkey that has a red bottom or the so-called red but.

Other types of monkeys can have other colored butts. Just for example, the Mandrills which are the largest of all monkeys have rainbow-colored butt.

There is a term used in Zoology which is called Callosity, an another name of Callus.

Callus is just a thickened and hardened portion of the skin or soft tissue, especially found in those body portions which are or have been subjected to repeated friction, irritation, and pressure.

Just like in our body, our feet are most likely to see calluses (thickened skin) found on the bottom of our feet, just on the bony areas that carry our weight.

The same happens in the case of other monkeys and baboons as well. When we refer to the hard red butt of baboons we term it as Ischial Callosities.

It’s called ischial because it forms thickened callus in the lower and back part of the hip bone i.e. in the butt portion majorly.

This thickened callus (Ischial Callosities) provides cushioning for the monkeys when they seat to support their body weight.

Baboons’ have colorful Ischial Callosities that not only help them to support their body weight while seating, but also as a display to attract male mates by the females.

Baboons’ Ischial Callosities are those hardened modified skin tissues that are composed of prominently thickened and cornified outermost layer of the epidermis with a subcutaneously dense fibro-fatty plate that fuses into the underlying periosteum by connective tissue.

The Ischial Callosities are composed of large blood vessels and lymphatic vessels that go deep into the skin layers. In fact, large arteries are also located in the superficial dermis just deep to the epidermis.

We also know that the blood contains Hemoglobin. These Hemoglobin molecules when bound to oxygen start to absorb blue-green light from the surrounding, and only reflect the red-orange light into our eyes. Thus, it aids in spreading the red hue and making the blood red in color.

So, due to the presence of numerous blood vessels with smooth muscular walls, and the swelling nature of the butt, the red hue of the blood flowing through the vessels gives the portion of the butt its red to light pink color depending on the number of vessels and thickened nature of the Ischial Callosities.

Here’s is the scientific meaning of Sexual Swelling in Baboons

Sexual Swelling in baboons is due to the filling and retention of blood, water, and other body fluids in the enlarged areas of genital and perineal tissues of the body, including the ischial callosities.

This sexual swelling causes the external and internal genitalia to swell forming edema and thus giving it a red to pink colored appearance.

So, the baboons that show swollen bottoms or swollen butt are actually due to the biological reason of Sexual Swelling.

Sexual Swelling is just a way to advertise the sexuality and mating readiness of the females to the males. This is because it indicates the time she is most fertile to reproduce. So, that’s why such swelling is also termed sexual swelling.

It is noticed that after every 34 to 37 days time period female baboons show swollen bottoms or the so-called sexual swellings.

The sexual swellings stay for about 14 days, with the swelling being gradually increasing in size throughout the female’s cycle days, beginning after menstruation. It is due to the increased estrogen levels throughout the female’s cycle days.

And so, during these 14 days time period, she is biologically prepared to enter into her heat phase and follicular phase and perform ovulation.

Just after the 14 days time period, there is a rapid decrease in swelling size which is actually due to the rising progesterone levels in their blood.

So, it can be clearly stated that when the swelling size increases, this indicates the increase of estrogen levels showcasing that the baboon is entering into her follicular phase from her first day of menstruation to the time ovulation occurs.

The time when ovulation occurs as mentioned above is the most fertile reproductive phase as during this timeframe if the female mates with the male, then the chances are the highest for her in getting pregnant.

And, when the swelling size decreases, this indicates the increase of progesterone levels and decrease of estrogen levels showcasing that the baboon is entering into her luteal phase.

During this timeframe of the luteal phase, if the female mates with the male, then the chances are the lowest to almost nil for her in getting pregnant.

Individuals can show moderate-sized to larger-sized swelling. And, the female baboons with larger swellings also have higher lifetime reproductive success because of their very good increase in estrogen levels. So, that’s also why such swelling is also termed sexual swelling.

Males are often attracted to those females who have larger swelling, thus giving the females more mating options.

Clarified: Female baboons can wish to get red and swollen immediately after the new male gains control of the troop

It is to be noted here that only the Female Baboons have a red swollen butt or we can say red swollen bottom. It is a sign that advertises the males that the females are ready to mate.

We already know that females swell after every 34 to 37 days time period naturally and it is a result of their hormonal surge during the menstrual cycle.

It has been reported in the wild that when a male baboon takes over a new troop and wishes to exert his dominance over the females, then he will always opt to kill the offsprings of the former alpha male so that he can reproduce with the females of that troop to make his own offsprings.

According to new research, it has been seen that males can also carry feticide as well. Meaning that the males will also attack pregnant females and cause them to miscarry.

And, during such situations when a new male gains control of the troop, females show various counter-strategies to protect the infants from getting killed by the males.

Some of the strategies include hiding the infants from the eyes of the male, fighting back, or also having red and swollen bottom immediately within a few days.

So yes, the female baboons can wish to get red and swollen immediately after the new male gains control of the troop in spite of having their infants. This is one of their most notable counter-strategies to stop male infanticide.

So getting red and swollen indicates the new male that the female is fertile (but is actually not) and ready to mate and so there are a lot more chances that he won’t kill the infants.

And so the female will mate with the new male but, the chances of the female being pregnant and successfully being able to reproduce is very little to almost none during the first cycles after the take-over.

The chances of the female baboon being pregnant and successfully reproduce is little to none after mating with the new male during such a situation because of their post-partum amenorrhea and inter-birth intervals.

So, it can be well-clarified that the female baboons can wish to get red and swollen immediately after the new male gains control of the troop just in order to offer the new males mating opportunities without actually allowing them to reproduce.

By following this counter-strategy, the females may increase their infants’ probability of survival and at the same time avoid the costs of being pregnant and lactating simultaneously.

Let’s also know about the Male Courtship behavior during the time when Females get swollen

According to some recent research, there is a direct correlation between sexual swellings and both female and male sexual behavior.

The males are mostly attracted to females with larger sexual swelling (or so-called Swollen bottoms). Whereas, the females have their so-called natural gift of swollen bottoms to attract males.

In some of the cases, it has been seen that the female opt to choose the best mate to have sex with her. While in other cases, many males will try to and will eventually compete to have forced sex with those females with larger swellings.

But not in all cases, the males will be attracted to females with swollen bottoms. Also note that baboons can mate all year round, though females are only sexually active during their cyclical estrus showcased by having sexual swellings.

Just for example, if a female has an infant that is less than one year old then she may not be willing to mate. And, in such a case the male will not show any interest in mating with her inspite of her large swelling.

And meanwhile, males may also show interest in females that have small to moderate-sized swellings if there are no better options available to them.

A female baboon will select the best male she thinks is strong enough to offer her nice offspring and provide her and her offspring with the best care.

In a various research, it was revealed that females often opt to choose to mate with young, high-ranking, newcomer males. Soon they start to form strong friendships with their mates during the subsequent conception cycles.

After a female selects a male, she will eventually mate with him if she opts to do so. And if everything goes right, the female will give the male’s sperm the best chance to fertilize her eggs by avoiding any further copulation by any other male, and the male will give his best to protect his female by fighting back other intruding males.

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