River Otters Killing Brown Pelicans in California: A Rare Predation Study

Wildlife researchers at Abbotts Lagoon in California’s Point Reyes peninsula discovered 73 dead brown pelicans killed by river otters over 19 visits. Recent observations suggest the pelicans may be learning to fly away when otters approach.

The study, led by Terence Carroll and Megan Isadore of the River Otter Ecology Project and published in the IUCN Otter Specialist Group Bulletin, highlights a rare predator-prey relationship between two recovering species in Northern California.

Researchers walked the shoreline every 7-10 days from June to November 2023, mapping and marking dead pelican locations to avoid double-counting. They found fresh dead birds on 17 out of 19 visits, with a maximum of 11 dead pelicans in one trip. The true death toll is likely higher due to scavenger activity and inaccessible shore areas.

Otters characteristically bite off pelicans’ heads and necks to access the chest meat, leaving distinctive marks that helped confirm otter kills. Data from eBird showed increased dead bird numbers during weeks with larger pelican gatherings, exposing lone birds at the flock’s edges.

Despite otters primarily eating fish and smaller birds, the high energy demands of swimming in cold water make large, slow-moving pelicans an attractive, energy-rich meal. Pelicans, weighing 3-4 kilograms, provide substantial food that otters can drag onto land.

Both species are conservation successes: brown pelicans were delisted from the US endangered species list in 2009, and river otters are recolonizing Northern California habitats.

Initial surveys showed pelicans did not avoid dangerous areas, but 2024 visits indicated a possible behavioral shift, with pelicans flying away as otters approached. This change was also observed at Rodeo Lagoon.

The study details the ecological impact, including otters transferring marine nutrients to land through leftover carcasses, which are consumed by coyotes. Pelican deaths peak during late summer and autumn, coinciding with migration patterns.

Although 73 deaths were recorded in 2023, the overall brown pelican population at Point Reyes remains stable, with the interactions representing a rare case of adapting species in shared habitats.