The Douroucouli monkey or Aotes is unique among the New World monkeys in being the only one that is truly nocturnal—night living. Uniqueness in nature is not a matter of chance or caprice, as it may sometimes seem to man, but is the result of selection and specialization for survival. In the douroucouli it is the eyes that are specialized: too sensitive to be exposed for long to the full light of day, but so sensitive that even in full darkness it can see such tiny objects as insects, one of its sources of food.
This determines the douroucouli on a night course in life. When the squirrel monkey is just contentedly snuggling its furry tail around itself and going to sleep, the douroucouli is emerging from the hollow tree trunk where it has spent the day sleeping. It is starting out to look for the insect and animal fare upon which its life depends. The sleep of the douroucouli is not profound by day, however, for there are many dangers abroad then. It must sleep half- alerted to them, so that when danger threatens, it can retreat to a safer spot.
In size the douroucouli is a little smaller than an ordinary cat. It is coloured a neutral shade of brownish-grey, which blends in perfectly with the twilight and night colours of the forest in which it moves, and with the shadows among which it catches its hours of half-sleep by day. The name Aotes, by which it is also known, comes from a Greek word meaning “earless,” which is at least the impression one gets from its face, the ears being small and covered with hair and lying close to the head.
The douroucouli’s face is dominated by a pair of large, round orange-yellow eyes, which give the animal a strangely soft and gentle expression. And, indeed, it is said to make a good pet, friendly though placid. It is prized in some areas of South America for its thoroughness in tracking down roaches and other insects in homes. The douroucouli, when it hunts in woods at night, calls in a wide variety of voices. It can twitter and squeak like many other monkeys, and it can sound a gong-like booming noise that is loud and far-carrying and is like that of no other monkey.
Like the squirrel monkey, to which it is related, the douroucouli is not one of those monkeys that can use its long, bushy tail for grasping. It is, however, extremely able with the hands it does have, which possess, as do man’s, thumbs that can be placed opposite to the fingers. Holding its food in one hand, the douroucouli can tear it apart easily with the other hand. The douroucouli, in common with certain others of the platyrrhini, often bears twins. Many other monkeys have only one offspring at a time.
Another New World monkey that often bears twins is the mannoset, which also is not a “true monkey.” However, in many respects it conforms more to what monkeys are thought to be than do some of the true monkeys themselves.