Examples of a monkey species in Indonesia may use stones for genital stimulation during play, a behavior noted in a study published in Ethology.
The study assessed dozens of long-tailed macaques, a population estimated between 700 and 1,000 individuals on Bali, observing deliberate rubbing of stones on the genital area to explore arousal or sexual motivation.
From the researchers’ perspective, these actions were not accidental. The team emphasized that the macaques did not get caught on their genitals while handling stones, indicating intentional behavior during social play and object manipulation.
This finding adds to a growing body of evidence that some animals use tools or objects not solely for practical tasks but also for pleasure or self-stimulation.
The research, published this month, relied on observations of a free-range macaque group around the Sacred Monkey Forest Sanctuary in Ubud, recorded during three periods from 2016 to 2019. The macaques frequently interacted with food provided by visitors, which complemented the field observations.
Long-tailed macaques. pixabay
To assess the potential use of stones for sexual stimulation, researchers analyzed 173 instances of stone manipulation by the monkeys, looking at behavioral cues and physiological indicators such as penile erection or signals of a fertile period to gauge sexual motivation.
Teenagers interact with others at higher levels than adults
The team reported that some individuals bumped into peers and touched their own genital areas with stones in response to the pleasurable sensations from these actions.
It was observed that younger macaques spent more time engaging in private-part stimulation than adults, especially during episodes of high arousal when mates were sought or signs of interest appeared.
The researchers noted that younger individuals displayed this behavior more frequently than mature ones, while acknowledging that the precise reasons behind this disparity remain unclear.
One possible explanation is that mature males maintain dominant positions, limiting opportunities for others, while younger monkeys might have relatively more free time to explore.
An additional study is needed to confirm these hypotheses and to understand how social structure and life stage influence such behavior in wild populations.
An example of a long-tailed macaque. pixabay
The study found that the observed behaviors tended to precede visible signs of sexual arousal and could persist beyond the initial arousal phase, a pattern not found in other forms of object manipulation. There appears to be a playful and intentional component to these actions.
The researchers concluded that instrumental behaviors with questionable adaptive value might endure through evolution, potentially serving self-rewarding or recreational purposes beyond immediate reproduction.
Reference report: https://onlinelibrary.wiley.com/doi/10.1111/eth.13324