Thousands of tourists flock to the Sacred Monkey Forest Sanctuary in Bali, Indonesia every year to see long-tailed macaques (Macaca fascicularis) in their natural habitat, MailOnline reported. But a new study showed that visitors could get more than what they are expecting.
Researchers studying these monkeys found that both male and female monkeys frequently use stone tools as tools to pleasure themselves. The findings provide new evidence for the sex toy hypothesis that the researchers proposed in an earlier study in 2020, which states that the self-stimulation activity of these monkeys is a form of tool-assisted masturbation.
"Self-Directed Tool-Assisted Masturbation"
Researchers from the University of Lethbridge said that males and females of different age groups of Balinese long-tailed macaques have different variations in using stone tools to pleasure themselves. Female monkeys were pickier with the stones they used, while young males were engaged with the activity the most.
Study lead author Camilla Cenni, a Ph.D. candidate at the University of Lethbridge in Canada, told Live Science that monkeys engage in genital stone tapping and rubbing regularly.
Some macaque populations regularly use stones as part of their behavior and play with them, either by rubbing on surfaces or bashing them together. Cenni noted that the behavior they saw is likely cultural because it is only seen in some populations.
The researchers described "self-directed tool-assisted masturbation" in their study, which likely stemmed from the wider stone use of the species. Although, this is a new type of behavior that has only been documented in the population of long-tailed macaques in Bali, Indonesia.
Cenni added that tool use in animals is usually about survival-dependent instances, like using it to crack nuts to eat them. But there is an increasing number of studies as well suggesting that some stone tool use does not have to be a matter of survival, and the Balinese long-tailed macaques are a clear example of this.
Self Sexual Stimulation in Animals
Scientists have long observed that some animals masturbate, such as chimpanzees, dogs, and porcupines. According to Newsweek, masturbation is common in non-human primates, albeit most of the observed cases were in captivity rather than in the wild. There were even some macaques seen sexually mounting sika deer, the first observed case of inter-species sexual behavior.
Masturbation in the animal kingdom is seen as a species' behavioral repertoire coincident with their mating system in their social groups. Researchers wrote in their study, titled "Do Monkeys Use Sex Toys? Evidence of Stone Tool-Assisted Masturbation in Free-Ranging Long-Tailed Macaques" published in the Ethology: International Journal of Behavioral Biology, that there is a strong association between the mating system of primates and male masturbation in which the behavior is often observed in multimale and multifemale organization system.
That system is also observed in macaques and seeing them using stones to self-stimulate is a rare case of an animal using stone tools to aid them in masturbation. Tool use in general is uncommon in the animal kingdom and is considered as a hallmark of intelligence in a species. For now, tool use for sexual pleasure is unexplored and is an unusually observed behavior.
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