1995, pp 61-74

Determinants of Nighttime Activity in “Diurnal” Lemurid Primates

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Abstract

Traditionally primates have been described as displaying either nocturnal (active only at night) or diurnal (active only during daylight hours) activity cycles. However, researchers investigating the behavior and ecology of Malagasy prosimian primates discovered that many species in the genus Eulemur traditionally labeled as diurnal also were active at night (E. f rufus: Sussman, 1974; E. mongoz: Sussman and Tattersall, 1976; Tattersall and Sussman, 1975; E. f. mayottensis: Tattersall, 1977; Tattersall, 1979; E. rubriventer: Overdorff, 1988; E. macaco: Colquhoun, 1993; E. coronatus and E. f. sanfordi: Freed, pers. comm.). While E. mongoz appears to seasonally switch from a diurnal activity cycle to a completely nocturnal activity pattern, other species such as E. fulvus and E. rubriventer have been observed to be active irregularly during both the day and night. These observations led Tattersall (1988) and Fleagle (1988) to propose and define the word “cathemeral” as a possible label for this unusual activity pattern. However, it has not yet been determined whether activity during the day and night is a seasonal phenomenon or a year-round pattern typical for Malagasy lemurids. There is evidence that some New World primates may be active day and night. For example, howling monkeys move and feed at night, although rarely (Dahl and Hemingway, 1988). In addition, Wright (1985, 1989) observed that the traditionally nocturnal night monkey (Aotus trivirgatus) was active during the day in Paraguay presumably due to the rarity of large diurnal raptors.