An extensive network of wildlife cameras took over 2 million photos to follow when tropical mammals are active and why, according to a study published in Nature Communications.
What wild animals do during the day is still a mystery. Researchers know they spend time eating, sleeping, and moving, but how and why they choose what to do is poorly understood. However, this information may be crucial to help conservation efforts. When they’re active, animals can be exposed to risks like hunting or other conflicts with humans.
To find an answer to these questions, a team of international researchers looked at more than 2 million photos of tropical mammals to find remarkable patterns of daily activities in many regions around the world. This work covers 166 species from 17 protected areas, including wild pig, gorilla, buffalo, jaguar, and tiger. Many captured species are listed as endangered, and many others we know very little about.
“The main determining factors of daily activity were body size and diet,” says Andrea F. Vallejo-Vargas, from the Norwegian University of Life Sciences and lead author of the study. “We suppose that there is a link between body size and so-called thermoregulation constraints.” The photos showed that large carnivores and omnivores were more likely to be active during the day than smaller species, even if they had the same diets. By contrast, larger herbivores were more likely nocturnal than smaller herbivores.
The larger the animal’s body, the more energy is needed to keep optimal body temperature in a warm climate. As a result, larger herbivores are active at night to save energy (which means they need less food). Animals that rely on insects were the only exception, and their pattern differed greatly across continents: larger species were more active during the day in America but not in Africa or Asia.
Not surprisingly, carnivores have activity patterns to match their prey. Curiously, small prey species tried to avoid top predators and were active at slightly different times. These choices may have cascading impacts further down the food chain. “For instance, we do not know whether the disappearance of top-predators in some protected areas affects the behaviour of prey, or whether the decreased abundance of prey affects the activity of predators and the possible cascading effects on the ecosystem, added Vallejo-Vargas.
What surprised the authors the most was the remarkable consistency across continents. “You would think there would be some variation between ecosystems as far apart as Africa and South America,” concluded Varllejo-Vargas. “There are large differences in species, particularly endemic ones. For example, there are no elephants or gorillas in the Amazon, nor armadillos in Malaysia.” However, there was very little difference in activity patterns. The authors believe these daily activity patterns may not involve the same animals but are shaped by similar processes and constraints among different regions. “Think of it as parallel evolutionary or ecological processes happening across the world at the same time, yielding the same results over and over.”
Vallejo-Vargas, A.F., Sheil, D., Semper-Pascual, A. et al. Consistent diel activity patterns of forest mammals among tropical regions. Nat Commun 13, 7102 (2022). https://doi.org/10.1038/s41467-022-34825-1