Bullying is not easy to define, namely because there is no one way to bully. It comes in many forms, from physical playground scuffles to verbal attacks. Even governments have a hard time defining it, often referred to as a repeated behaviour with the intent to hurt someone either physically or emotionally. By this definitions, there are many ape and monkey bullies, too. In fact, any hierarchical society is likely to have bullies in its midst.

An unfortunate monkey at the bottom of the hierarchy is repeatedly attacked and picked upon by those higher up in the group - they are sometimes beaten up every day. Bullying amongst rhesus macaques, for example, seems to release tensions among the higher-ups. Bullying seems to reinforce their bonds, a ...

Unlike most mammals, mature male orangutans exhibit different facial characteristics: some develop large 'cheek pads' on their faces (as shown above); other males do not. A team of researchers studied the difference in reproductive success between cheek-padded males and males without cheek pads. They found that those with cheek pads are significantly more successful in fathering offspring.

Source: http://link.springer.com/article/10.1007%2Fs00265-015-1991-0 ...

Proboscis monkeys have four-part stomachs, enabling it to regurgitate food so it can chew and swallow it again.

The two marmosets - small, New World monkeys - had been a closely bonded couple for more than three years. Then, one fateful day, the female had a terrible accident. Her partner left two of their infants alone in the tree and jumped down to apparently comfort and mourn her. Humans mourn their dead, of course, and some recent studies have strongly suggested that chimpanzees do as well. This new observation suggests that mourning is more widespread among primates than previously thought.

Zookeepers at Central Park Zoo in the US assumed their cotton-top tamarins were falling silent every time someone entered their enclosure, but spectrograms, which provide visual representations of sound, revealed what was really going on. These little monkeys were actually whispering their alarm calls instead of shouting them, which is the first evidence of whispering in a non-human primate species.

This is the pygmy marmoset (Cebuella pygmaea), the smallest known monkey in the world.

They are found in western Brazil, southeastern Colombia, eastern Ecuador, eastern Peru, and northern Bolivia and they typically live in the understory of the rain forest near rivers. Males weigh around 140 grams (4.9 oz), and females only 120 grams (4.2 oz).