Animals Are Becoming Nocturnal
This time it's because of rising temperatures
Hiya!
Evolution is a peculiar phenomenon. Generally speaking, a trait evolves to help a species adapt to a changing environment. Our ancestors needed to live on the ground instead of in trees, so evolution changed the shape, size, and capabilities of hominin bodies and intelligence.
More recently, experts have noticed many animal species are evolving to become more nocturnal. What might entice a species to transition if they’re used to being active during the day? Researchers say there are two primary reasons: Us and climate change.
Human Activity
In a 2018 study published by the journal Science, scientists at the University of California, Berkeley, and Boise State University performed a meta-analysis of 76 studies that analyzed the Human (anthropogenic) impact on the behaviors of 62 mammal species from six continents — including boars, deer, tigers, and sun bears.
Take the sun bear, for instance. In its natural habitat, the sun bear spends over 80 percent of its 24-hour cycle awake and active during the day. But that changes dramatically when humans enter the picture. In areas where humans are spreading into the sun bear’s natural habitat, the bears switch to spending 90 percent of their time awake at night.
The authors point out that many animal species are being pushed to the geographical margins of their habitats because of us, leaving them few options to avoid us. The researchers write since we’re encroaching on their physical habitats, the animals are “separating themselves in time rather than in space.”
The team concluded that humans have a “strong effect” on the daily patterns of wildlife activity. In total, animals increased the time spent being active after dark in response to human activity by an average factor of 1.36. They explain in the study:
“For example, an animal that typically split its activity evenly between the day and night would increase its proportion of nocturnal activity to 68% of total activity near human disturbance. Of the 141 effect sizes, 83% corresponded to an increase in nocturnality in response to humans. This finding indicates a widespread increase in nocturnality among mammals living alongside people.”
It didn’t seem to matter what human activity occurred, either. Even nonlethal ones like hiking drove animals to hide out until the risk of running into us dropped, which is typically after dark. National Geographic has a great interactive graph showing the changes in animal behavior when avoiding humans using the data from this study.
Using time to avoid us humans is a pretty ingenious adaptation, but every change has ripples. So, while becoming more nocturnal may aid some animals, we have no idea how this might affect the broader ecosystem. While only time will tell, we may learn sooner than expected since scientists found that even more animals are becoming nocturnal for a different reason — climate change.
Climate Change
We aren’t the only reason a species increases its nocturnal tendencies. Rising daily temperatures are also driving animals to spend their waking time during the cooler night hours. This might seem like no big deal — if anything, it’s a rational solution — but this behavior change can tell us a lot about a species.
It’s one thing for animals to become more nocturnal to avoid us, but understanding the conditions in which an animal becomes nocturnal due to temperature fluctuations can help scientists better predict responses to climate change. It can also tell us more about different species’ vulnerabilities to heat.
Unfortunately, little research exists on the subject, though it’s not a completely barren field. Previous studies have found similar behavioral shifts in other animals, including cheetahs and giant anteaters. Now, doctoral candidate Michaela Peterson at Vanderbilt University is adding her study, published in October 2023 in Biotropica, to the pile of research.
Peterson and her team studied the white-lipped peccary, a native to Central and South America. The animal looks like a hairy pig with a white snout and typically forages vegetation during the day and sleeps at night.
From November 2021 to October 2022, the researchers set camera traps to record the white-lipped peccary’s activity and microclimate data loggers to measure air temperature on a fine spatiotemporal scale around their habitat in the Pantanal biome of Brazil.
After analyzing the data, they found the white-lipped peccaries were most active in the afternoon when daily temperatures averaged a balmy 80°F (26°C) or less. They shifted to become more active in the morning on days when the weather was slightly warmer, but once the average high reached 94°F (34°C), the peccaries became most active after sunset.
Another study, published on January 17, 2024, in the Proceedings of the Royal Society B, found that alpine goats can be added to the list of animals shifting toward nocturnal habits to beat the heat.
Now that this switch in animal behavior is becoming more well-known, I suspect more studies will follow. As global temperatures continue to rise, we’ll likely learn of even more animals making this shift, but scientists also hope to learn more about the knock-on effects this behavior change has.
Switching to a nocturnal schedule to avoid heat might seem like a simple solution, but there are drawbacks for some animals. For instance, alpine goats don’t see well at night, making foraging more challenging. Not to mention having to deal with a new range of nocturnal predators like pumas in the case of the white-lipped peccaries or wolves for the alpine goats.
Perspective Shift
How might this influence hunting methods and prey preferences? Will foraging animals find enough to eat in the dark? And, of course, I’m curious what physical adaptations species may form — like maybe the alpine goat will evolve eyes better suited to seeing in the dark. I guess we’ll just have to wait to find out, though.
Humans are just one of countless species sharing this planet, and we will all be forced to adapt to global warming. We humans are (mostly) using advanced technologies to help us adapt, but other species don’t have the luxury of ordering an air conditioner to be delivered.
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Fascinating