Almost everything a monkey does, from picking through a friend’s fur to screaming a warning, is about managing relationships within its group. Even the clever stuff, like cracking food open with stones, tends to spread because young monkeys copy those around them. Monkeys are smart in practical, social ways rather than human-like ways, and they still fail some tests that small children pass.
Why Monkeys Groom Each Other
If you watch monkeys at a zoo or park, one will part the other’s fur with its fingers and pick out dirt, flakes and insects. The groomed monkey often relaxes, lies down, or offers a new body part to work on. Pairs tend to take turns, and the same pairs groom again and again, so who grooms whom is a good clue to who the friends are.
It’s tempting to think this is just hygiene. Cleaning is real, but monkeys spend far more time grooming than cleaning would require, and the effort is concentrated on favored partners, which cleaning alone wouldn’t explain. The hormone response tracks the friendship, not just the touch. In wild chimpanzees, close primate relatives of monkeys, levels of the bonding hormone oxytocin rose after grooming with a close friend but not after grooming a casual partner.1PubMed Central. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees That held whether or not the partners were related or interested in mating.2PubMed Central. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees In capuchin monkeys, oxytocin also rose after grooming and after fur-rubbing, where monkeys rub plant juices on each other.3Georgia State News Hub. Oxytocin Linked To Social Bonding In Gregarious Capuchin Monkeys
Grooming also works like a currency between friends. It costs a monkey time and attention, so who it chooses to groom is a real signal of who matters to it. Because the cost is real, grooming partners are more likely to support each other later, for example by sitting nearby or joining a dispute. Grooming can also calm a tense relationship, which is why monkeys sometimes groom a higher-ranking group member to ease the tension around them.
Bonds can start early, through handling babies. In rhesus macaques, relatives who handled an infant often formed stronger bonds with it later in life, but unrelated handlers usually did not.4Behaviour. Infant handling enhances social bonds in free-ranging rhesus macaques (Macaca mulatta) In white-faced capuchins, females mostly handled the babies of females they already groomed and allied with.5PubMed. Infant handling in wild Cebus capucinus: testing bonds between females
How Monkeys Use Tools and Solve Problems
Wild capuchin monkeys in Brazil use stones and sticks to dig up underground food.6PubMed Central. Wild capuchin monkeys use stones and sticks to access underground food They don’t grab any rock nearby. They pick stones of suitable size and shape, strike or scrape repeatedly, and sometimes reposition the stone. They also appear to adjust their grip on a digging stone, using its pointed or angled edges.7PubMed Central. Wild capuchin monkeys use stones and sticks to access underground food Wear marks left on stones show that the same ones get used again. Not all monkeys use tools; capuchins and some macaques are the standouts.
Before using a tool, a monkey has to link an action to a distant result, such as pounding a nut to reach the kernel inside. It also has to choose an object that fits the job, since a stone that is too light or too round won’t do the work. Handling the tool well takes practice, so young monkeys often spend months fumbling before they get results.
Habit matters as much as ability. When two wild bearded capuchin groups faced the same new probing puzzle, only the group already used to stone tools in many settings tried stones to solve it.8PubMed Central. The effects of tradition on problem solving by two wild populations of bearded capuchin monkeys in a probing task A group without the habit may not think of tools at all, even if it’s capable.
How Monkeys Learn From Each Other
Young monkeys watch selectively. Young capuchins pay most attention to foragers eating rare or hard-to-process foods,9PubMed Central. Social traditions and social learning in capuchin monkeys (Cebus) which means they focus on exactly the skills that are hardest to work out alone. Young foragers, especially females, also tend to adopt the same techniques as their close companions.10PubMed Central. Social traditions and social learning in capuchin monkeys (Cebus)
A new habit usually starts when one monkey discovers a trick, often by trial and error. Tolerant friends sit close and watch, and successful demonstrators get watched more than unsuccessful ones. When researchers introduced a new food-extraction puzzle to wild capuchins, the solution spread through groups by watching others.11PubMed Central. Social tolerance and success-biased social learning underlie the cultural transmission of an induced extractive foraging tradition in a wild tool-using primate Over months, the technique becomes the group’s local way of doing it.
Watching isn’t always exact copying. A monkey can learn that a food is worth working on just by seeing others handle it, then work out its own way to get at it. Copying the exact movements is a stronger form of learning and is harder to prove, which is why researchers distinguish the two. Monkeys and apes can imitate body movements, a skill linked to brain cells that fire both when doing and watching an action.12PubMed. Social learning, culture and the ‘socio-cultural brain’ of human and non-human primates
In a simple sense, this is culture. Different groups of the same species can have different habits, and those differences come from learning, not genes or environment alone. Monkey traditions are fewer and simpler than human ones, but they are real.
What Monkey Calls and Faces Mean
Vervet monkeys give alarm calls for leopards, eagles and snakes that sound clearly different from one another.13PubMed Central. Vervets revisited: A quantitative analysis of alarm call structure and context specificity Each call tells listeners what kind of danger is present, not just that something is wrong. Leopard alarms send vervets up into trees, eagle alarms make them look up or dive into bushes, and snake alarms make them stand and scan the ground. That’s far more useful than a single general scream, and it’s one of the clearest cases of animal sounds that work somewhat like words, though they are much simpler than human language.
Vervets also judge calls by what they refer to, not just how they sound: after learning to ignore a bird’s raptor warning, they also ignored their own eagle alarm.14Animal Behaviour. The assessment by vervet monkeys of their own and another species’ alarm calls And context matters. The same male bark alarmed vervets far less when rival groups were already meeting, since the bark then had an obvious explanation.15PubMed Central. Context-dependent alarm responses in wild vervet monkeys
Faces carry social meaning too. In rhesus macaques, a silent bared-teeth face used peacefully goes with less serious fighting and more grooming between monkeys who meet often.16PubMed Central. Signaling Context Modulates Social Function of Silent Bared-Teeth Displays in Rhesus Macaques (Macaca mulatta) A threatening face with a direct stare makes macaques follow that monkey’s gaze faster.17PubMed Central. Monkeys integrate facial expressions and direct gaze to modulate gaze-following behavior
A silent bared-teeth face, with lips pulled back and the mouth mostly closed, is often a peaceful or submissive signal in macaques. The same teeth on display in a different setting, such as a monkey cornered by a larger one, can signal fear. A wide open mouth with a stare is usually a threat, and staring back can be read as a challenge. The message depends on who is making the face, who is receiving it, and what just happened between them, so look at the whole body and situation, not the teeth alone. A monkey’s “smile” at a tourist shouldn’t be read as friendliness.
Do Monkeys Understand Fairness
Researchers test this by teaching monkeys to hand over a small token in exchange for food. Then they give a partner a better reward for the same token and watch whether the first monkey keeps taking part. A control condition, such as giving the better food without a partner nearby, shows whether the reaction is about the partner or just about the better food.
Capuchins trading tokens for food reacted badly when a partner got a better food for the same task.18PubMed Central. Inequity responses of monkeys modified by effort This is the famous cucumber-versus-grape reaction: a monkey happy with cucumber may refuse it after seeing a partner get a grape, and some throw the food or stop cooperating. Refusal was strongest when they had to work hard while watching the partner get the better reward.19PubMed Central. Inequity responses of monkeys modified by effort Male capuchins also chose equal outcomes more often when a partner was involved than when no partner was.20PubMed. Attending to the outcome of others: disadvantageous inequity aversion in male capuchin monkeys (Cebus apella)
The results aren’t uniform. In another test with female capuchins, seeing a partner get better food made no difference.21PubMed. Does inequity aversion depend on a frustration effect? A test with capuchin monkeys (Cebus apella) Monkeys likely notice when they lose out, but how strongly depends on the setup.
Fighting, Making Up, and Rank
After a fight, Japanese macaque victims scratch, self-groom and shake their bodies more, all signs of stress.22Animal Cognition. Reconciliation and variation in post-conflict stress in Japanese macaques (Macaca fuscata fuscata): testing the integrated hypothesis The stress is greater when the opponent is a relative.23Animal Cognition. Reconciliation and variation in post-conflict stress in Japanese macaques (Macaca fuscata fuscata): testing the integrated hypothesis Former opponents often approach each other within minutes. They may groom, embrace, lip-smack, or sit touching, and the subordinate becomes less fearful while the dominant becomes less aggressive. After reconciling, victims’ stress signs dropped below their usual calm level, and further attacks became less likely.24Animal Cognition. Reconciliation and variation in post-conflict stress in Japanese macaques (Macaca fuscata fuscata): testing the integrated hypothesis In long-tailed macaques, a fight reduced how well the pair could share food, and a friendly reunion restored it.25Animal Behaviour. Post-conflict reunions and reconciliation in long-tailed macaques
Monkeys tend to make up more with partners whose relationship is valuable to them, such as close friends or relatives. A fight with a valued partner puts more at stake, since losing cooperation costs more.
Rank affects stress in less obvious ways. Low rank does not always mean more stress; subordinates have higher stress hormones mainly when they face many stressors and lack friends or relatives for support.26PubMed. Are subordinates always stressed? A comparative analysis of rank differences in cortisol levels among primates Friends and kin give grooming and backup in fights, so monkeys without them absorb more stress from rank. In some groups, top-ranking monkeys showed higher stress hormones, especially under prolonged strain.27PubMed Central. Relationship between Social Rank and Cortisol and Testosterone concentrations in Male Cynomolgus Monkeys (Macaca fascicularis)28PubMed Central. Social status predicts physiological and behavioral responses to chronic stress in rhesus monkeys
How Smart Monkeys Really Are
Monkeys share with humans an approximate sense of number, judging which pile is bigger without counting.29Primate Neuroethology. Behavioral Signatures of Numerical Cognition In tests, they’re shown two collections of food or objects and tend to choose the larger one. Like people, they find close quantities harder to tell apart than distant ones,30PubMed. Analog numerical representations in rhesus monkeys: evidence for parallel processing so a large difference is easy and a small one is hard.
Monkeys also seem to have at least a basic form of understanding what others know, though not the full human version.31Yale Daily News. Monkey business reveals theory of mind In practice, it means a monkey acts differently depending on whether another animal has seen or heard something. Wild geladas mating with a female’s non-partner were quieter and tended to mate when the main male was more than 20 meters away.32PubMed. Evidence for tactical concealment in a wild primate They seemed to adjust to what he could see or hear. Still, about 20% of these sneaky matings led to attacks from the cheated male.33PubMed. Evidence for tactical concealment in a wild primate
The limits show up at the mirror. Capuchins given a mirror did not remove a sticker placed on their own forehead.34PubMed. Revisiting the mark test for mirror self-recognition Most monkeys seem not to recognize themselves in mirrors, unlike great apes and young children. A monkey often treats the reflection as a stranger, threatening or ignoring it, and may use the mirror to look at things behind it without linking the image to itself.
Old World monkeys, such as macaques and baboons, score about as well as apes on many physical and social tests.35PubMed Central. Old World Monkeys Compare to Apes in the Primate Cognition Test Battery So claims that monkeys are “as smart as” something deserve care. Monkeys excel at tasks tied to their real lives, like food and social rivals, and a test designed for humans may not measure monkey ability fairly.
Why Monkeys Act Differently Around People
At a Malaysian tourist site, long-tailed macaques spent about half as much time interacting with each other when people were around, 8.6% versus 17.7%.36PubMed Central. Effect of Human Activity and Presence on the Behavior of Long-Tailed Macaques (Macaca fascicularis) in an Urban Tourism Site in Kuala Selangor, Malaysia They also fed on natural food less, 9.9% versus 12.8% of the time.37PubMed Central. Effect of Human Activity and Presence on the Behavior of Long-Tailed Macaques (Macaca fascicularis) in an Urban Tourism Site in Kuala Selangor, Malaysia Urban monkeys go further, developing new habits in where they live and what they eat to survive in cities.38The International Encyclopedia of Primatology. Primates in Urban Settings
Fed monkeys become bold because monkeys learn quickly from each other where food comes from. A few successful grabs can spread the habit through the group, and bold monkeys may lose natural foraging skills over time.
Even well-meant feeding is harmful. Human food is often high in sugar, salt, or fat compared with what monkeys naturally eat. Feeding also draws them into crowded areas near roads and people, where injuries and conflicts are more likely.
So don’t feed wild monkeys, keep food out of sight, and keep a few meters away. Avoid direct staring, which can read as a threat, and don’t carry visible food or plastic bags. If a monkey bares its teeth with a stare, back away calmly. Monkey bites can transmit infections, so get any bite checked.