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.
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.
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
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