By Allie Wilkinson
Rather than avoiding water that washes up the beach like other foraging shorebirds, the mallards allow themselves to be lifted by the water and deposited down the beach. (Also see “Inside the Curl: Surfing’s Surprising History.”)
After catching a wave, the ducks will then stick their bills in the sand and sweep them from side to side to catch the quick burrowing Pacific sand crab.
Scientists first witnessed this surf-feeding on the sandy beaches at the Coal Oil Point Reserve near Santa Barbara (map) in May 2011, but their Internet search found people reporting observations of the behavior dating back to November 2010.
What’s more, people have observed the behavior in various West Coast locations spanning as much as 800 miles (1,300 kilometers), from San Diego County up to Coos Bay, Oregon—suggesting that it is not just a local phenomenon, according to the study in the latest issue of The Wilson Journal of Ornithology. The birds have been seen “surfing” alone, in pairs, and in flocks.
“I had been surfing the same beach for 30 years when one day I started seeing ducks wading around” where the water washes up the beach, study leader Kevin Lafferty of the USGS Western Ecological Research Center said by email.
“It was comical and took me by surprise. We were also doing research on the sandy beach food web and thought, ‘Here’s a player we hadn’t thought of,'” he said.
Duck See, Duck Do
The only other ducks known to feed on sand crabs are called surf scoters: Specialized sea divers that usually plunge into the surf zone in search of food, but will sometimes feed in the area where waves wash ashore. Another type of bird called the black brant will also sometimes feed on sand crabs in the surf zone. (See National Geographic’s backyard bird identifier.)
Pacific sand crabs are an important part of the sandy beach food web and account for 80 to 90 percent of the total mass of invertebrates in the intertidal zone, making them an abundant, easy to find protein source.
Lafferty and team suspects that the behavior is a result of mallards relative comfort around people.
The ducks thrive in the wetlands and parks near California’s sandy beaches, and as their numbers rise, more birds are setting off in search of new habitats—including the beach. Once there, it’s possible the mallards have witnessed the other birds feeding in the surf and are mimicking them in a case of “duck see, duck do,” the scientists say.
Eating sand crabs carries risks to the ducks, though. The crabs carry acanthocephalan and trematode parasites, which can infect the mallards and have unknown health consequences. Other risks include exposure to surf, stress from exposure to people or dogs, and high salt intake.
So the next time you’re in California, don’t be surprised if you see mallards catching some waves. It just may inspire you to grab a board and give it a try for yourself.