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Crepuscular, a classification of animals that are active primarily during twilight, making them similar to nocturnal animals. Diurnality, plant or animal behavior characterized by activity during the day and sleeping at night. Cathemeral, a classification of organisms with sporadic and random intervals of activity during the day or night.
Night monkeys have large brown eyes; the size improves their nocturnal vision increasing their ability to be active at night. They are sometimes said to lack a tapetum lucidum, the reflective layer behind the retina possessed by many nocturnal animals. [8] Other sources say they have a tapetum lucidum composed of collagen fibrils. [9]
Many nocturnal creatures including tarsiers and some owls have large eyes in comparison with their body size to compensate for the lower light levels at night. More specifically, they have been found to have a larger cornea relative to their eye size than diurnal creatures to increase their visual sensitivity: in the low-light conditions. [2]
Like other night monkeys, the Panamanian night monkey has large eyes, befitting its nocturnal lifestyle. But unlike many nocturnal animal species, its eyes do not have a tapetum lucidum. Also like other night monkeys, it has a short tail relative to the body size. [7] The Panamanian night monkey is arboreal and nocturnal. [6]
The eyes are large, even larger than those of nightjars. As in many species of nocturnal birds , they reflect the light of flashlights. [ 14 ] Their eyes, which could be conspicuous to potential predators during the day, have unusual slits in the lids , [ 15 ] which allow potoos to sense movement even when their eyes are closed.
Their eyes are disproportionately large, having the largest eye-to-body weight ratio of all mammals. [12] These huge eyes provide this nocturnal animal with excellent night vision. [13] In bright light, the tarsier's eyes can constrict until the pupil appears to be only a thin spot.
The aye-aye is a nocturnal and arboreal animal meaning that it spends most of its life high in the trees. Although they are known to come down to the ground on occasion, aye-ayes sleep, eat, travel and mate in the trees and are most commonly found close to the canopy where there is plenty of cover from the dense foliage.
The most noticeable feature of the pygmy tarsier are its large eyes, which are about 16 mm (0.63 in) in diameter. Unlike other nocturnal species, tarsiers lack a tapetum lucidum due to the diurnal evolutionary history of primates. [8] To make up for this, tarsiers have evolved their large eyes to maximize available light. [8]