Lunar Philia in a Nocturnal Primate

Abstract

The influence of moonlight on behavior has been well documented for many nocturnal mammals, including rodents, lagomorphs, badgers and bats. These studies have consistently shown that nocturnal mammals respond to bright moonlight by reducing their foraging activity, restricting their movement, and reducing their vocalizations. Lunar phobia among nocturnal mammals is generally believed to be a form of predator avoidance: numerous studies indicate that predation increases during moonlit nights. A study I conducted at Tangkoko Nature Reserve in Sulawesi, Indonesia, demonstrates that spectral tarsiers, (Tarsius spectrum), are not lunar phobic, but are lunar philic; they become more active during full moons. During full moons, spectral tarsiers increased foraging, decreased resting, increased travel (distance traveled per unit time, nightly path length, and home range size), increased the frequency of group travel and decreased the frequency of olfactory communication. I explore several potential hypotheses to account for the lack of lunar phobia and potential increased risk of predation resulting from this unusual behavior. Two hypotheses that may account for the behavior are that: 1) foraging efficiency increases during full moons and outweighs the increased risk of predation, and 2) predation risk is not greater during full moons. Instead, predation risk increases during new moons.