MISSOULA — This edition of A Wilder View takes a look at how the brightness of the moon can change the behavior of animals. A hunter’s moon illuminates the forest floor and while animals are out and about utilizing the extra light, predators are fast asleep.
Approximately 44% of mammals are classified as nocturnal, while 26% are primarily active during the day and 29% are either active during twilight hours such as early mornings and evenings or active during irregular times of the day based on when food is acquired.
A recent study looked at the effects a full moon can have on mammals as the extra light enhances their vision.
Bright moonlight is widely believed to increase predation risk for nocturnal mammals by increasing the ability of predators to see their prey. But the moonlight actually increases the chances for a predator to be seen by their prey.
The full moon's brightness increases the activity of prey animals that use eyesight as their primary sensory system and suppresses the activity of species like bats, rodents, and rabbits that primarily use other senses like smell and sounds.
Those animals that rely primarily on vision may be more efficient at locating their food with a bright moon, and they may also experience a lower risk of being eaten because their ability to detect predators should increase.
Since predators are more likely to be seen during a full moon, they’re much less active as compared to a night with no moonlight. This is especially true in more open areas like a field.
Although mammalian predators in this study were less active with moonlight, they found that nocturnal bird predators such as owls may be more active.
Many mammalian predators rely on stealth and ambush to capture prey, whereas birds may rely more on speed, and this difference could lead to opposite effects of moonlight on mammalian and bird predators.
Overall, the study found that the magnitude of moonlight effects on activity level was large enough to indicate that moon phases likely have a major impact on the feeding rates and habitat use of many species.