Why Are the Monkeys at Golden Hill Literally Turning Gold?

Kowloon Reservoir is a pretty magical place, especially for someone like me who gets easily overwhelmed by all the trappings of big city life. It’s not Hong Kong’s largest reservoir, nor is it the most beautiful, but it’s probably the best place in our wild urban jungle to get up close and personal with amazing wildlife within a relatively small proximity.

Situated at the base of what’s fondly called ‘Monkey Hill’, my wanderings through Kowloon Reservoir are never complete without encountering at least one large troop (group) of chattering macaques. Though many of the city’s residents seem wary of these playful primates - often brandishing sticks or hiking poles to wave ominously if any of the monkeys get too close - I find that the macaques show no interest in people unless they have food or make direct eye contact.

Anyway, over the last few weeks (Nov, 2023), I started noticing a strange phenomenon. Almost every time I visited Kowloon Reservoir, I began to encounter rhesus macaques with golden coats – far different to the regular greys, browns and auburns that macaques naturally possess.

As my curiosity got the better of me, I started delving deeper into why Golden Hill’s Monkeys are turning gold.

While the history of Hong Kong's macaques requires an article all of its own, these are the main statistics that put the current population into context.

• According to the Agricultural Fisheries and Conservation Department (AFCD), there are approximately 1,800 macaques in Hong Kong, though I've also seen stats saying the population is closer to 2,000 now.
• The macaques are split up into 30 distinct social groups
• A social group of macaques, sometimes called a troop, can have up to 200 monkeys in it
• A population census conducted in the ‘90s indicates that there were once 3 distinct species of macaques found in Kowloon Reservoir
• These species included rhesus (Macaca mulatta) 65.3%, long-tailed (M. fascicularis) 2.2%, Tibetan (M. thibetana) 0.2%, and hybrids 32.3%
• Other sources claim that macaque species like Japanese macaques and even a pig-tailed macaque have also been reported in Kowloon Reservoir – though a long time ago
• Currently, it appears that the tibetan, japanese and pig-tailed macaques are gone from the area. The long-tailed macaques, which were seen regularly throughout the ‘70s and '80s also seem to have vanished, along with obvious hybrids.
• If you want to see macaques in Hong Kong, they can be found in Kam Shan (Golden Hill), Lion Rock, and Shing Mun Country Parks.

As it turns out, golden rhesus macaques have been spotted in colonies from Pakistan all the way to Puerto Rico! Scientists studying these unique primates state that the typical defining traits of a golden macaque are a "visually distinct pigmentation pattern resulting in light blonde colored fur [and] consistent hypopigmentation (lighter skin tone)." From my observations, the lighter skin tone in Kowloon Reservoir's golden rhesus macaques is most notable on fingers and toes.

Apart from their skin pigmentation and fur color, there is almost no other difference in health or behavior patterns between golden macaques and regular macaques. Golden macaques even "maintain the typical 2-toned body pattern of the species." The only possible additional difference is that golden monkeys may face higher instances of retinal hypopigmentation, possibly leading to compromized eyesight later in life.

It should be noted that golden macaques are born with their unique coloration and retain the same golden shade for life. They will never redevelop a new coat that matches the color of their troop.

As far as I could tell from observing at least five unique golden rhesus macaque individuals within Kowloon Reservoir, they were not shunned by regularly colored macaques. Images from other studies also showed golden rhesus macaques coexisting peacefully with macaques of a regular shade.

In Kowloon Reservoir, I witnessed several golden rhesus macaques that were integrated perfectly into different family groups. I also spotted a baby macaque sticking close to its mother.

None of the golden rhesus macaques I came across were isolated or appeared to be operating independently of family groups. This leads me to believe that the golden coloration is well tolerated by regular macaques and does not lead to the abandonment of golden-colored individuals.

Given that there are several golden rhesus macaques within Kowloon Reservoir across different troops (including at least one baby that I witnessed), I believe that the golden coloration does not make macaques incapable of finding mates. I cannot state, though, whether the golden coloration makes them less desirable as mates.

Theory 1: Hybrids - False

At first, I thought that perhaps the presence of other species of macaques in Kowloon Reservoir may have led to a few hybrids being born with golden fur. However, the golden macaques that I observed were all rhesus macaques with no physical traits that indicated hybridization.

Another problem with the hybrid theory is that the tibetan macaque, pig-tailed macaque, Japanese macaque and long-tailed macaque don't naturally have bright gold or yellow fur.

Finally, even the second-most prevalent species of macaque - the long-tailed macaque - "has virtually disappeared together with easily-recognisable hybrids."

Theory 2: Gene Mutation - True

Gene mutation is the actual reason why golden macaques exist. "The “golden” rhesus macaque (Macaca mulatta) phenotype is a naturally occurring, inherited trait," meaning that it can be passed down from generation to generation.

It is believed that the golden phenotype is linked to "3 different variants in the TYRP1 and TYR genes." Variations in these genes is also known to cause pigmentation changes in other species and is "associated with...albinism in humans."

The gene is recessive, which is why you don't see too many golden monkeys in the wild.

Golden rhesus macaques are exceedingly rare in nature, which is what makes their presence in such large numbers at Kowloon Reservoir particularly baffling.

At least three separate scientific journals corroborate that in the wild only, 1 in 10,000 macaques is golden.

With such low odds of seeing a golden macaque in the wild, why are there so many in Kowloon Reservoir?

One reason for the high concentration of golden rhesus macaques is that despite the population of rhesus macaques in Kowloon Reservoir numbering only around 1,500 individuals (80% of Hong Kong's total macaque population), this still results in a high concentration of macaques living in a relatively small area.

With no new macaques being introduced to diversify the macaque gene pool, it's inevitable that the 'golden monkey' recessive gene will keep popping up in Kowloon Reservoir.

There is also a distinct lack of predators in Kowloon Reservoir that prey on macaques. This means that while a golden coat would mean greater conspicuousness in the wild and a higher chance of being spotted and consumed by predators, this gene mutation bears no consequence in Hong Kong. As such, the golden monkey gene can continue to be passed on without any of the ramifications it might incur in areas with suitable predators.

A similar instance has occurred in Cayo Santiago, an island in Puerto Rico, where the golden rhesus macaque population has ballooned to "8–52 times greater than what is estimated to occur in the wild, likely the result of...the small number of trapped monkeys used to populate the island."