Earth

Some tropical mammals shy away from the full moon

Full moon rising over a misty rainforest. Some tropical mammals, like those in the Indonesian rainforest, avoid the moonlight.
View at EarthSky Community Photos. | Roosevelt Silva captured this setting full moon over a misty rainforest in Brazil on May 26, 2021. Thank you, Roosevelt! Scientists recently discovered that some tropical mammals, like those in Brazilian tropical forests, avoid the moonlight.
  • Many mammals in tropical forests adjust their behavior based on moon phases, with some species becoming less active during the full moon.
  • Using wildlife cameras, researchers observed that about 30% of mammals in these habitats are less active when the moon is full, while 20% are drawn to the moonlight.
  • The study highlights concerns about how increasing artificial light and forest canopy loss may disrupt animal behavior and interactions in tropical ecosystems.
  • The 2025 EarthSky Lunar Calendar is now available! A unique and beautiful poster-sized calendar. Keep up with all phases of the moon every night of the year.

    Some tropical mammals avoid the full moon

    On a night like tonight – when there’s a full moon in the sky – the landscape is lit by bright moonlight. And you might think mammals living on the floor of tropical forests would welcome the moonlight. After all, it helps them see better. But scientists at the Norwegian University of Life Sciences studied the behavior of animals in the tropics under varying conditions of moonlight. They said on October 15, 2024, that – while some tropical mammals do appear more active under bright moonlight – an even larger percentage is less active when the moon is full.

    The researchers published their findings in the peer-reviewed Proceedings of the Royal Society B on October 16, 2024.

    Nighttime lighting affects tropical mammals

    Scientists don’t know a lot about how tropical mammals behave under different levels of moonlight. Their habitat – the floors of tropical forests under a thick canopy of leaves – are some of the darkest places on the planet at night.

    So scientists used automatic wildlife cameras to observe how mammals behaved during the night under different phases of the moon. They found at least half of the mammal species altered their activity around the full moon. Some became less active, in an effort to be inconspicuous and avoid predators.

    Richard Bischof of the Norwegian University of Life Sciences said:

    Imagine playing hide-and-seek in a dark room, and then somebody lights a candle. The light, even if it is weak, may make it easier for you to find your way around the room. But if you are the one hiding, you suddenly become a lot easier to detect.

    A large rodent with body stripes on the forest floor in a black and white image.
    Some tropical mammals, such as this paca, avoid the full moon and are less active when there is more moonlight. This image is from a wildlife camera. Image via Tropical Ecology Assessment and Monitoring Network/ Norwegian University of Life Sciences.

    Studying wild mammals in the dark

    The researchers studied 2.1 million wildlife camera images collected by the Tropical Ecology Assessment and Monitoring Network. The data came from 17 protected forests in Asia, Central America, South America and Africa.

    Of the 86 tropical mammal species they observed, the scientists found 12 of them strongly avoided moonlight at night. Just three species were drawn to moonlight.

    Bischof commented:

    These were the species with the most pronounced reactions. However, half of all the species responded to lunar phases. Either by changing their nocturnal habits, altering their overall activity levels, or both.

    Of the mammals that changed their behavior, the scientists discovered about 30% of them kept a low profile during the full moon. This was especially the case for nocturnal rodents. And about 20% of mammal species were drawn to the full moon.

    A dark image showing an armadillo on the forest floor.
    A nine-banded armadillo captured on a wildlife camera in the Caxiuana National Forest, Brazil. These armadillos are not fans of the full moon and are less active when there is more moonlight. This image is from a wildlife camera. Image via Tropical Ecology Assessment and Monitoring Network/ Norwegian University of Life Sciences.

    Why does this study matter?

    Tropical forests hold a significant portion of Earth’s biological diversity. These wild places are being increasingly fragmented and cleared. Logging reduces the forest canopy, allowing more light through. Artificial light from streetlamps and buildings can also influence animal activity.

    Bischof explained:

    The key takeaway from our research is that light affects animal behavior. It raises further questions about how changes in illumination affect species activity.

    The effect of increasing light on wild tropical mammals

    About 30% of tropical mammal species avoid the full moon, in part by becoming less active. A degraded tropical forest that lets in more light does not bode well for these species and could upset a delicate ecological balance.

    Bischof said:

    If these results extend to artificial light, loss of dark nights could curtail the amount of time animals invest into foraging and other important activities.

    There is a risk that we are fundamentally altering both species composition and species interactions in tropical forest communities through light conditions alone.

    Bottom line: Scientists have found that half of all mammal species in tropical forests change their behavior based on phases of the moon. About 1/3 of them avoid the full moon.

    Source: The moon’s influence on the activity of tropical forest mammals

    Via Norwegian University of Life Sciences

    Read more: Light pollution causes insects to lose track of the sky

    Posted 
    November 15, 2024
     in 
    Earth

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