The animal on the cover of Programming Social Applications is a Diana monkey (Cercopithecus diana), an endangered monkey found in areas of West Africa, including Liberia, Sierra Leone, Ghana, and Côte d’Ivoire. Its name comes from the characteristic white stripe (or browband) across its forehead, which was thought to resemble the bow of Diana, the Roman goddess of the hunt. Its dark, sleek fur is contrasted by this telltale browband, as well as a white throat, underarms, and stripes on the thighs. It is considered one of the most beautiful of the Old World monkeys.

Diana monkeys dwell in primeval forests. They do not make nests, though they retreat to higher levels of the trees at night. They’re rarely found on the ground, as they’re able to sustain their diet of insects, fruit, invertebrates, young leaves, and flowers at all levels of the canopy. The monkeys’ main predators include leopards, crowned hawk-eagles and other birds of prey, chimpanzees, and humans. To protect themselves from predators, Diana monkeys dwell in groups, usually consisting of one male and around 10 reproducing females and their offspring. In addition to alerting their fellow group members to danger, Diana monkeys sound distinct alarm calls for different predators. Their reproductive biology isn’t very well understood, but it is known that their mating system is polygynous, breeding takes place year round, and females generally produce one offspring at a time.

Diana monkeys are classified as vulnerable ...

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