A new Harvard study published in the Journal of Animal Ecology reveals that predator animals are less active on most moonlit nights, while prey animals that exhibit visual acuity and have more habitual cover, such as lemurs, are more active.

Many nocturnal prey animals perform activities under the cover of darkness to protect themselves from predators. Scientists traditionally suspected that these prey animals are less active on bright nights when increased moonlight enhances predators’ ability to detect them.

However, the new study conducted by Harvard research associate Christopher D. Golden ’05 and University of Alaska-Fairbanks professor Laura R. Prugh found that moonlight does not necessarily increase predation risk—the extra light also gives prey increased ability to detect predators.

“What we found was that if predators were benefited by moonlight, then the prey may also benefit,” Golden said.

The study examined the effects of moonlight on the activity of 59 nocturnal mammal species. The researchers investigated factors such as habitat cover preference, visual acuity, taxonomy and trophic level—an animal’s position on the food chain.

“Our results were unanticipated because we had thought that the effect of moonlight would be moderated by the influence of a species’ trophic level,” Golden said.

Golden and Prugh said that they were surprised to discover that trophic level did not play a huge role in predation risk in animals. Instead, the scientists found that prey species with vision as their primary sensory system were more active in the moonlight, whereas prey species with other primary senses were less active.