Animals Gone Rogue After Dark

Wildlife doesn’t follow the rulebook when it comes to daily schedules. New research reveals that many mammals don’t stick to being strictly day or night creatures, especially in areas with increasing human presence.

A groundbreaking global study analyzing nearly 9 million camera trap images across 38 countries found that long-held scientific assumptions about when animals are active may need significant revision.

The research, published in Science Advances, compiled data on 445 species and discovered that fewer than half matched their traditional classifications as day-active (diurnal), night-active (nocturnal), twilight-active (crepuscular), or irregularly active throughout the 24-hour cycle (cathemeral).

“Our argument was largely based on anecdotal evidence, but this research project truly quantifies that wildlife species don’t fit specifically within these parameters, and our changing environment influences their activity,” said Humberto Perotto, associate professor in the Texas A&M Department of Rangeland, Wildlife and Fisheries Management.

Perotto contributed data from his research in the Edwards Plateau region, where camera traps originally set to study Rio Grande wild turkeys captured a wealth of information about other wildlife passing through the area.

The international research team found that of 445 species documented, only 39% matched their established activity patterns in scientific literature. Many regularly switched between different activity periods.

“The most striking thing is that when you are taught an animal is diurnal or is nocturnal, that is not always correct,” said Brian Gerber, former University of Rhode Island research ecologist and project co-author. “Many terrestrial mammals will be diurnal sometimes and nocturnal or cathemeral other times. When you see a nocturnal species during the day, this is perhaps not as unusual as you might think.”

Several factors influence when animals are active, including body size, geographic location, and notably, human presence. The researchers observed that mammals in North America became more nocturnal in areas with higher human development.

“As we humans develop land and encroach into wildlife habitat, this land-use change causes new behaviors in wildlife,” Perotto explained.

These behavioral shifts aren’t without consequences. Animals forced to change their active hours may struggle to find food, avoid predators, or reproduce successfully.

The study found that smaller mammals were more likely to be nocturnal worldwide. Species with larger geographic ranges showed more flexibility in their activity patterns, switching between day and night depending on local conditions.

Available daylight had the strongest influence on activity timing, with many species adjusting their schedules seasonally as daylight hours changed. However, human footprint and distance from the equator also prompted significant shifts in behavior.

The research team used data from 200 camera trap projects across six continents, representing more than 10,000 years of combined camera monitoring. The Texas A&M contribution came from approximately 56 camera traps that were originally set to study wild turkeys but captured data on numerous other species.

This extensive collection of standardized data allowed scientists to create the first global comparative analysis of mammal daily rhythms, revealing nuances that smaller, localized studies couldn’t detect.

“Further research is needed to better understand these implications and identify ways to mitigate potentially negative impacts,” Perotto said. “Studies like this are advancing science and helping us understand how our changing world affects the rhythms of the natural world.”

The findings suggest that wildlife management and conservation efforts need to consider the flexibility of animal behavior rather than relying on rigid categories of when animals are expected to be active.