Night monkeys

The night monkeys, also known as the owl monkeys or douroucoulis, are the members of the genus Aotus of New World monkeys (monotypic in family Aotidae). The lifespan of a wild night monkey is unknown; however, they have a lifespan of 20 years in captivity. The total population of night monkeys is similarly unknown, as the monkeys live near the canopies of deciduous forests, making counting the monkeys very difficult. Night monkeys constitute one of the few monkey species that are affected by the often deadly human malaria protozoan Plasmodium falciparum, making them useful as non-human primate experimental models in malaria research.

Ecology
Night monkeys can be found in Panama, Colombia, Ecuador, Peru, Brazil, Paraguay, Argentina, and Bolivia. The species that live at higher elevations tend to have thicker fur than the monkeys at sea level. The night monkey can live in forests undisturbed by humans (primary forest) as well as forests that are recovering from human logging efforts (secondary forest).

Physical Characteristics
Night monkeys have big brown eyes and therefore have increased ability to be active at night. Their ears are rather difficult to see, and their genus name, “Aotus,” means “earless” because of this. Both male and female night monkeys weigh virtually the same amount. Night monkeys can weight anywhere from 1.76 lbs to 2.76 pounds. The male is slightly taller than the female, measuring 1.14 feet and 1.12 feet, respectively.

Behavior and Intelligence
The name “night monkey” comes from the fact that all species are active at night and are in fact the only truly nocturnal monkeys (an exception is the subspecies Aotus azarae azarae, which is cathemeral). Night monkeys make a notably wide variety of vocal sounds, with up to eight categories of distinct calls (gruff grunts, resonant grunts, screams, low trills, moans, gulps, sneeze grunts and hoots), and a frequency range of 190-1,950 Hz. Unusual among the New World monkeys, they are monochromats, that is, they have no colour vision, presumably because it is of no advantage given their nocturnal habits. They have a better spatial resolution at low light levels than other primates which contributes to their ability to capture insects and move at night. Night monkeys live in family groups of the mated pair with their immature offspring. Family groups defend territories by vocal calls and scent marking. The night monkey is socially monogamous, and all night monkeys form pair bonds. Only one infant is born each year. The male is the primary caregiver, and the mother only carries the infant for the first week or so of its life. This is believed to have developed because it increases the survival of the infant and reduces the metabolic costs on the female. It is not uncommon, however, for a female night monkey to “evict” a male night monkey and find another mate.

Taxonomy
Until 1983, all night monkeys were placed into only one (A. lemurimus) or two species (A. lemurinus and A. azarae). Some authors still believe there are only two or three true species, the remaining taxa being subspecies of these. An often-used distinction is an even split of eight species between a northern, gray-necked group (A. lemurinus, A. hershkovitzi, A. trivirgatus and A. vociferans) and a southern, red-necked group (A. miconax, A. nancymaae, A. nigriceps and A. azarae). Arguably, the taxa otherwise considered subspecies of A. lemurinus – brumbacki, griseimembra and zonalis – actually should be considered separate species, whereas A. hershkovitzi arguably is a junior synonym of A. lemurinus. A new species from the gray-necked group was recently described as A. jorgehernandezi. As is the case with some other splits in this genus, an essential part of the argument for recognizing this new species was differences in the chromosomes. Chromosome evidence has also been used as an argument for merging "species", as was the case for considering infulatus a subspecies of A. azarae rather than a separate species. Fossil species have (correctly or incorrectly) been assigned to this genus, but only extant species are listed below.

Classification
Family Aotidae
 * Aotus lemurinus (gray-necked) group:
 * Gray-bellied night monkey, Aotus lemurinus
 * Panamanian night monkey, Aotus zonalis
 * Gray-handed night monkey, Aotus griseimembra
 * Hernández-Camacho's night monkey, Aotus jorgehernandezi
 * Brumback's night monkey, Aotus brumbacki
 * Three-striped night monkey, Aotus trivirgatus
 * Spix's night monkey, Aotus vociferans
 * Aotus azarae (red-necked) group:
 * Azara's night monkey, Aotus azarae
 * Peruvian night monkey, Aotus miconax
 * Nancy Ma's night monkey, Aotus nancymaae
 * Black-headed night monkey, Aotus nigriceps