When the Wild Things Are: Groundbreaking Study Provides New Insights into Human Impacts on Wildlife Activity

The advent of wildlife camera traps on public lands and in backyards has fascinated the public with a wealth of imagery reflecting the antics of animals as they roam, hunt, wallow and care for young.  Now, a newly published study incorporating camera trap imagery from thousands of sites around the world is dramatically correcting the scientific understanding of the time of day wild mammals are active while also demonstrating how humans impact animal activity. Recently published in Science Advances, the groundbreaking work assembled a team of more than 200 researchers–including study co-leader Kadambari Devarajan, a former NE CASC fellow, and NE CASC Research Ecologist Toni Lyn Morelli–to collect data on 445 wildlife species ranging from American bison to gorillas.  

According to Devarajan, the study’s principal discovery is that much of what scientists thought they knew about animal activity is wrong. The team found that existing diel classifications, or official descriptions of when wildlife are active, were accurate for only 39% of all species studied. Out of the species studied, 74% switched phenotypes.

“Species are often classified as diurnal, nocturnal, or crepuscular and sometimes cathemeral, as if these are immutable phenotypic traits,” said  Devarajan. “When an animal is active is certainly impacted by the species’ evolution, but it’s also a behavioral response to its environment.”

As Devarajan explains, human activity has become increasingly influential on wildlife activity as the world population has grown and people push into wildlife habitats via construction or recreation activities. The study reveals that some animals have different diel activity depending on their location in urban or rural environments. The study data on elk capture this point perfectly. For example, when human activity near the animals was low, they were highly cathemeral, or active both day and night; as human activity increased, they became highly nocturnal.  Likewise, human activity had the effect of increasing nocturnality in the striped skunk, snowshoe hare, gray fox and North American porcupine.

“The most striking thing is that when you are taught an animal is diurnal or nocturnal, that is not always correct,” said Brian Gerber, study co-leader and a USGS researcher.  “Many terrestrial mammals will be diurnal sometimes and nocturnal or cathemeral other times. When you see a presumably nocturnal species during the day, this is perhaps not as unusual as you might think.” 

To complete the project, the research team created a camera trap dataset from 20,080 camera sites across 38 countries, six continents, and myriad environments such as arid desert, rainforests, arctic tundra, and savanna grasslands. Working together, team members leveraged 8.9 million observations to create an enormous, updated library of standardized activity estimates.

The study examined how the general “global human footprint” affects diel activity. Because the researchers were looking at data from both urban and wild locales, they saw some species become more diurnal and others more nocturnal. Overall, a third of species studied were affected by the human footprint measure.

Diel activity aids understanding of animal distribution and abundance, critical measures that are used to determine species endangerment and legal harvest levels. In addition, updating the classifications helps scientists understand how animals are adapting to climate change.

“Recognizing the fitness consequences of species’ diel phenotype plasticity and lack thereof is an important next step to understand the impacts of environmental change and can help direct conservation efforts that are more critical than ever,” Gerber said.

This article was adapted from a press release by the University of Rhode Island.