Early one morning in 2018, Megan Isadore was observing wildlife at Abbotts Lagoon, along the northwestern edge of Point Reyes National Seashore, when she noticed something splashing in the water. At first, the co-founder of the River Otter Ecology Project thought it could have been anything — the area is home to a wide variety of species including thousands of waterfowl and shorebirds, as well as mammals such as weasels and bobcats. 

Isadore saw it was a brown pelican, which wasn’t unusual. The diving waterbirds liked to spend the nonbreeding season resting at the site. But this one’s wings were flapping in a way that struck her as abnormal. “I could see it struggling, but I couldn’t figure out why,” she told SFGATE over the phone.

The movement all but stopped as the bird’s head was pulled underwater by an unseen force. Then, the head of a river otter popped to the surface, chewing.

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“I realized the otter had grabbed the pelican, killed it by drowning it, and was starting to eat it,” Isadore said. “I was with a couple of other people who were somewhat horrified.” 

She had never observed the hunting behavior herself before. Over the next couple of years, Isadore regularly checked her camera traps, which she had been previously using to monitor river otters in the area as part of her nonprofit’s mission to preserve the health of local watersheds. She found an increasing number of pelican carcasses littering the shoreline, and it fascinated her. 

A view of Abbotts Lagoon.

Typically, river otters seek out prey closer to their own size: cormorants, surf scoters, gulls and ducks, or smaller creatures like crustaceans and amphibians. “They’re very fierce and hungry little animals,” Isadore said. “They’ll get whatever’s plentiful and easiest to catch.” 

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But she learned it was the first time in decades that a river otter had been observed drowning a brown pelican, a species Isadore said otherwise has few known predators. The last reported instance of the behavior was in 2006, at Rodeo Lagoon in the Marin Headlands, with another one-off instance in 1998 at Lake Tolowa in Del Norte County. It has never been documented outside of California. 

Questions raced through Isadore’s mind. Both river otters and brown pelicans are recovering species that have rebounded from low numbers historically caused by pollution, habitat loss and lack of hunting regulations. Were the otters killing enough pelicans to cause a problem for the population at large? Would the pelicans begin to leave the area in response to their peers’ killer instincts? And how did the behavior........

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