Researchers at Cal Poly Humboldt have discovered that North American river otters at the Arcata Marsh and Wildlife Sanctuary shift to a nearly all-duck diet during the winter, using dense vegetation and underwater ambushes to hunt migratory waterfowl.
“We found that they actually were eating ducks almost exclusively during the winter months,” researcher Gina Culver said.
By analyzing otter scat — a process Culver jokingly called a “dirty job” — researchers identified prey species, including buffleheads and ruddy ducks, by comparing recovered feathers with museum specimens.
As thousands of migratory birds gather at the marsh each winter, otters use dense vegetation and underwater ambushes to hunt diving ducks before they can escape.
Jeff Black, a professor at Cal Poly Humboldt who leads the long-running research project, calls river otters the “wolves of the wetlands.”
Culver said the animals may appear “cute and adorable,” but they are also apex predators and an important keystone species.
For people hoping to witness the hunting behavior themselves, Culver offered a simple tip.
“Look for the ducks that are flying frantically off the ponds and then look there,” she said.
The research also relies heavily on citizen science. Local residents report sightings through QR codes, helping researchers track a population estimated at about 82 otters in North Coast wetlands.
Researchers say the otters’ continued success at the marsh reflects the health of one of the North Coast’s most important wetland ecosystems.
“River otters are known to have low tolerance to polluted water, so their presence is a really good indicator of a healthy ecosystem,” Culver said.
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- Gina Culver, researcher, Cal Poly Humboldt University
