When the Wild Things Are

Children as young as five start learning about the diel movements of animals, that is, their behavior relative to the time of day. They learn that racoons and bats are active at night and giraffes and kangaroos like to romp around in the daytime. But apparently most animals haven’t been to kindergarten, because a new study that included work by University of Maryland researcher Travis Gallo found that more than half of mammals don’t adhere to their diel classification in accepted scientific literature, and many animals switch their behavior based on environment and nearby human activity.

The study, published in the journal Science Advances, was led by researchers from the University of Rhode Island who analyzed camera trap data on more than 400 mammal species from 20,080 camera sites across 38 countries in six continents.

In total, the researchers collected 8.9 million observations of animals ranging from American bison to African polecats, and in environments that varied from deserts and rainforests to savannas, the artic tundra and even cities. What they found was surprising.

Existing classifications for an animal’s diel activity were accurate for only 39% of all species studied. In addition, 74% of the animals observed switched traits, with some becoming more nocturnal and others more diurnal. Because the study looked at data from both urban and wild locales, the researchers were able to detect a global human footprint that impacted nearly a third of animal species. Some urban adapted animals, like the striped skunk, snowshoe hare, gray fox, and North American porcupine became more nocturnal with increasing human footprint.

Gallo was not surprised by that shift, because for years he has been helping answer questions about if and how animals adjust their daily rhythms to adapt to environmental change, especially in urban environments. The new findings track with a study he published in 2022 that characterized the diel behavior of 8 mammals in 10 U.S. cities, and found that some species adjust their activity to manage risks associated with urbanization. That data was included in the current study along with other data from Gallo and more than 200 authors.

Although light availability played a role in the animals adapting their diel behavior, the team found that increasing environmental change caused by people impacted mammals, primarily in North America. The study suggests that as environmental change encroaches on wild spaces, species that cannot shift or adjust their behavior may be negatively impacted.

Animals’ diel activity is important for better understanding changes in their distribution and abundance, which is critical for conservation initiatives and for determining a species endangerment and legal harvest levels.

For Gallo, it is also critical for understanding the potential for human wildlife interaction. Today, Gallo is focused on characterizing the interaction between urban mammals and humans, especially as it relates to disease transmission. One of his research projects includes monitoring the overlapping movements of white tailed deer and humans in and around Washington, D.C., to understand if and how they may be spreading diseases like COVID.

“A study like this is a testament to open data sharing and collaboration,” Gallo said. “No single research team would have been able to collect animal observations across every continent except Antarctica and discover these global trends in animal behavior. It was exciting for me to see data from my past and current studies have a new life and contribute to these interesting results.”

The study, When the Wild Things Are, was led by Brian Gerber, a University of Rhode Island research ecologist now with the U.S. Geological Survey at Colorado State University, and Kadambari Devarajan, URI research fellow and affiliate at the time of the study. It was published in the journal Science Advances.