New in Wildlife Science: Cardinal Gut Health, Killer Squirrels
The fittest cardinals have the most gut microbial diversity; why squirrels are killing voles; global insect activity increases nearly a third at night
- By Laura Tangley
- Wildlife Science
- Jun 25, 2025
Clues to Cardinal Fitness Found in the Gut
For those who routinely knock back yogurt, kombucha and other microbe-packed foods, the link between good health and a diversity of “good bugs” in the gut is well accepted. But despite a few lab studies, scientists know little about whether such correlations hold true among wild animals, especially birds. To explore the question, biologists at Florida Atlantic University (FAU) took an in-depth look at the (above), a striking and abundant backyard songbird. Over five years, the researchers sampled the cloacal microbiomes of 74 wild male and female cardinals then assessed several traits associated with fitness, including weight and the vividness of red on a bird’s beak and feathers. Publishing their in Oikos, the biologists found that the cardinals they assessed to be most fit also hosted the highest levels of gut microbial diversity. Among other applications, the finding could boost the success of captive breeding of bird species that are endangered. Because they live in different habitats and eat different diets than wild birds, “captivity changes the bacterial communities of birds,” says lead author and FAU biologist Morgan Slevin. “By showing how the gut microbiome relates to host fitness, we hope our research leads to ways to improve animal health in captivity.”
Attack of the Killer Squirrels?
Think of ground squirrels, and you’ll likely picture these familiar rodents with cheek pouches stuffed full of seeds, nuts, grains and other typical vegetarian fare. But a recent , published in the Journal of Ethology, reveals that the also has a carnivorous side—hunting, killing and consuming in the wild (above). Lead author and University of Wisconsin–Eau Claire biologist called the scientists’ observations “shocking … we had never seen this behavior before.” In summer 2024, however, they saw it frequently: Of 74 observed interactions between the two species, 42 percent involved squirrels actively hunting the smaller rodents. Smith and her colleagues suggest the squirrels’ switch to carnivory was triggered by a local and temporary vole population explosion at their study site in California’s Briones Regional Park. The findings suggest that ground squirrels are more opportunistic than previously believed. Co-author and University of California, Davis, biologist says that such behavioral flexibility “might help them persist in environments rapidly changing due to the presence of humans.”
Things That Go Buzz in the Night
Summer picnickers battling flies, ants and yellow jackets that compete for alfresco feasts may be surprised by this news: According to the first global review of insect-activity patterns throughout the day–night cycle, nearly a third more insects are active after dark. Compiling results of 99 studies published from 1959 to 2022, researchers from the University of Western Australia in Nature Communications that global insect activity increases on average 31.4 percent at night. Nocturnal insects range from familiar fireflies and moths to mayflies, caddisflies and katydids (leaf-mimic katydid, above). The authors suggest many reasons for greater nocturnal activity, including avoidance of diurnal predators such as birds and fishes. With many insect populations declining, they also say the results highlight the threats of artificial lighting, which biologist and lead author calls “detrimental to nocturnal insects, disrupting their natural behaviors.”
Microscope
Freshwater Extinctions
In a global assessment of more than 23,000 species, an international team of scientists in Nature that about a quarter of freshwater animal species—including fishes, crabs, shrimps and crayfishes (pictured)—are threatened with extinction.
More from National Wildlife magazine and the National Wildlife Federation:
Moths Work the Night Shift »
How Light Pollution Impacts Wildlife & How You Can Help »
Lakes on the Line »
