Experts believe Japan’s Monkey King, the woman who violently overthrew their troop’s male leader to be its first female leader since 70 years ago could lose her title at mating time.

Yakei is a female Japanese macaque, and the alpha female leader of a troop of 677 monkeys in Takasakiyama Natural Zoological Garden, Oita, southern Japan. 

According to the reserve, Yakei was nine years old and had fought her mother as well as three male high-ranking officers.

Now, experts are anticipating that Yakei could lose the top spot during the current breeding season, which runs from November until March. 

In Japanese macaque societies, there is strong social hierarchy. This gives the highest-ranking members access to food first. 

Yakei (pictured) is a female Japanese macaque, and the alpha female leader of a troop of 677 monkeys in Takasakiyama Natural Zoological Garden

Yakei is a Japanese macaque female and leader of the troop of 677 monkeys that live in Takasakiyama Natural Zoological Garden.

Takasakiyama Natural Zoological Garden in Oita, southern Japan was established as a reserve for monkeys in 1952

Takasakiyama Natural Zoological Garden, Oita (southern Japan) was established in 1952 to protect monkeys.


Japanese macaques are matrilineal soldiers that can range in size from 20-30 individuals to over 100. 

The availability of food is an important constraint to troop size. An alpha female troop leader and an alpha male troop commander are responsible for the overall success of the troops.

The troop is often dominated by females, which are usually three to one. They also rank according to a hierarchy passed down from mother to child. 

Alpha males are responsible for the fathering of offspring and providing leadership to the group’s movement.

The time that males reach sexual maturity is when they disperse and then transfer to other troops for the rest of their lives. 

The migration of males to another troop occurs every 2 years. 

Source: New England Primate Conservancy 

Takasakiyama Natural Zoological Garden began as a monkey reserve in 1952. But, in its 70 year history, Takasakiyama Natural Zoological Garden has not had a female head the macaque colony. 

Takasakiyama has two Japanese macaque monkey troops, comprising around 1,500 of the creatures in total. Staff call this ‘troop A’. Yakei leads them.   

Last April, Yakei beat up her own mother, Nanchu, 31, to become the top-ranking female of troop B. 

And as if all that wasn’t enough, she brutally overthrew Sanchu in June, the alpha male aged 31 who was leader of troop A for five years.    

A hostile takeover by a female is very rare in Japanese macaque society, according to Yu Kaigaishi, a researcher at the Japan Society for the Promotion of Science.

Kaigaishi stated to the New York Times that only a handful of cases had been reported in primatology’s history. 

Experts know Yakei is the leader of the troop thanks to the ‘peanut test’ – providing the monkeys with peanuts and seeing who eats first. Yakei’s status was confirmed when males and women stepped aside for her to eat. 

Kaigaishi says Yakei displayed some behaviors that are ‘typically only seen in dominant males.’ They include shaking branches and walking up with her tail.

Kaigaishi stated that she thinks it is like she behaves like an adult male and acts more aggressively than the other people around her. 

Pictured is the Takasakiyama Natural Zoological Garden in 2018. Staff keep an eye on the behaviours of the two Japanese macaque troops

Pictured is the Takasakiyama Natural Zoological Garden in 2018. Staff keep an eye on the behaviours of the two Japanese macaque troops

Wild Japanese macaques inhabit here on the hills of Takasakiyama, one of very a few natural zoological gardens in Japan where wild moneys can be observed in close proximity

Here, wild Japanese macaques live on Takasakiyama’s hills. This is one of the few natural Japanese zoological parks where wild moneys are easily observed.

Yakei has been the dominant rooster for over half a century, however, it is currently breeding season and Yakei’s involved in a “simian love triangle” that could cause her distress, according to witnesses.      

After Goro bit Yakei in the face, Yakei was paired up with Goro (15 years old) during an earlier breeding season.

Whether or not it was intended as a come-on, it caused Yakei’s bottom to flush bright red – a sign she wanted Goro as a mate. 

It’s well known that many primates, like baboons, undergo obvious physical changes when they’re sexually ready – notably, swelling of the perineal skin and sexual organs becoming redder. 

Goro isn’t interested in Yakei, but Yakei has now taken control of the troop. 

Japanese macaques are medium-sized, stocky monkeys with relatively short tails. Sexually dimorphic in size, males are twice as large as females

Japanese macaques have medium-sized tails and are stocky, large monkeys. The size of males is twice that of females, and they are sexually dimorphic.

Meanwhile, another 18-year-old high-ranking male called Luffy has recently tried to woo Yakei, but rather than returning any interest, she appears fearful of him.    

Kaigaishi stated that she visited Takasakiyama and saw Yakei display a “fear grimace”, which is a common expression for people who are subordinate to Luffy. “Also I saw Luffy push Yakei to take over the food monopoly.

The apparent subservience sign could indicate that Luffy may take control of the troop during mating season when aggressive behaviours could occur.     

As the primate soap opera is continuing, experts from the reserve will be captivated by what lies ahead.  


Japanese macaques consider courtship an important aspect of reproductive success.

Japanese macaques are known to spend an average of 1.6 days in courtship with their potential partners. This time they travel, feed, nest and travel together.

Lower ranking males have a tendency to stay longer with females who are with males of higher rank. If a male of high rank observes a female with potential mates, they might try to interrupt their courtship. 

Copulation can take place either arboreally (in the trees) or terrestrially (on the ground). Two types of mating call are available to females. One is the squawk, or squeak which is vocalised before and after copulation. It is vocalized after copulation and sounds similar to an atonal cackle. 

Japanese macaques have a polygyny; both males and women in Japan are able to reproduce with any available individual and can also have multiple partners during the breeding season. 

The sexual maturation age of Japanese macaques is 3.5 years for females, and 4.5 years for males. 

Even though males as young at 1.5 years old have been seen mounting females in the wild, it is not common for them to successfully conceive until their older age. 

Most breeding takes place between March-September. It can take between 157 and 188.5 days for a gestation to occur. 

Females who are ready for birth usually move out of the troop to find safe, private places. 

Japanese macaques typically have one offspring when they breed. It is rare to have twins and they only occur in one of every 488 births. 

In some Japanese macaques, weaning can occur within 6-8 months. Mothers may, in some cases, continue to care for their children up to 2.5 years after they give birth if there have been no previous births. 

Although this is not common, female Japanese macaques are capable of producing a fully viable baby up to the age of 25. It is not known if fertility and menopause are related. 

Unfortunately, many female Japanese macaques were seen carrying the corpses of stillborn babies. Sometimes, this behavior can last several days. 

Infanticide can also be committed by males. The male may be able to reproduce faster if he is not pregnant.