Piracy on the Pacific: Bald eagle robs a sea lion of its lamprey lunch
BY Sarah Keartes FEBRUARY 09 2018The last time birds and lampreys shared a spot in one of our headlines, the primitive fish were being dropped from the sky by hungry gulls. Now, the two have converged in a very different but equally fascinating sighting: a photographer in California has captured the moment a bald eagle stole a lamprey lunch from a sea lion's jaws.
The incredible set of images was captured by photographer and eagle enthusiast Frank Coster in Jenner, California, a small coastal town in Sonoma County. Tucked away atop a bluff on North America's Pacific coast, Jenner is a known hotspot for interesting wildlife sightings. The water here is cold and rich in nutrients; the pristine coastline is flanked by a 5,630-acre swathe of protected redwood forest; and the Russian River forms a breathtaking estuary where it joins the sea.
Thousands of harbour seals use the Russian River estuary as a nursery each year, and with pupping season running from March through to August, the animals have begun to show up in droves in recent weeks. Other portly pinnipeds, like elephant seals, northern fur seals and California sea lions also take advantage of the estuary's shelter and abundance of food ... and the local eagles have noticed.
"I took these photos at the mouth of the river," says Coster. "It was not until the last several months that I personally have seen eagles actively stealing (or trying to steal) from sea lions and harbour seals."
Much to his amazement, Coster watched on as one of the daring birds swooped down to snatch a lamprey – an eel-like animal that slurps its food with a sucker-like rasping mouth structure – straight out of a sea lion's jaws.
Interestingly, Jenner isn't the only spot in California where this robbing strategy has been documented. Back in 2013, photographer Bradley Oliver witnessed similar behaviour off the coast of San Fransisco. During that encounter, the sea lion actually attempted to chase down the avian thief, but the eagle managed to escape unscathed, with its fishy spoils in tow.
"It's an absolute prize series of shots!" Cascades Raptor Center Executive Director Louise Shimmel says of Coster's photographs. "I haven't seen this behaviour before, but bald eagles are such kleptoparasites that it doesn't totally surprise me. They steal from each other constantly, and from osprey all the time."
Ospreys (also known as "sea hawks") have a unique "bait and tackle" set of adaptations that makes them incredibly successful at fishing. Spiked pads on their feet help with gripping slippery prey, and reversible outer toes lock cargo down during flight. And yet, they regularly lose their lunch to their white-headed cousins:
"Young osprey typically need to learn to just let go, or they get hurt," says Shimmel. "We get them in with talon punctures to the breast and shoulders from such interactions."
According to Coster, the sea lion didn't put up much of a stand either. It seems that even for a hulk of blubber and brawn weighting up to 350 kilograms, a full belly isn't worth the risk of potentially serious injury.
Despite their propensity for scavenging and stealing, bald eagles are apt hunters capable of taking down animals as large as deer, and their talons can reach five centimetres (2in) in length.
Jenner local Joan Bacci, who has been observing the town's eagle population for five years, has seen the impressive birds race seal lions for the same lamprey. "Sometimes the eagles win, and sometimes the sea lions win," she says. "But we rarely see them engage. The eagles generally pick a different spot on the beach than the hauled-out seals.
Stealing food might take far less energy, but there's another potential reason behind the bald eagle's act of piracy here.
Sea lions tend to shake lampreys above the water in order to dismember them before eating (we've seen the pinnipeds do this with sharks as well), and during all this thrashing activity, a sea lion's head may "stand" about a metre above the surface. Since bald eagles are unable to take off from the water (unlike ospreys, who regularly submerge themselves), this gives them a shot at landing an easy meal without getting wet.
It's still a risky tactic: one wrong move from the sea lion, and this eagle may have been forced to "swim" to shore.
Just how a defensive sea lion may have reacted to that turn of events is hard to say, but exhaustion would probably pose a bigger threat to a water-bound eagle in that scenario.
"To my knowledge no one has witnessed a sea lion or seal kill or eat an eagle," says Coster, who, along with Bacci, is a contributing member of the Jenner Bald Eagles Study Group.
On the other hand, a lengthy voyage towards shore has been known to cause bald eagles to drown.
One of the area's resident female bald eagles has recently gone missing, and it could be that a mishap during a theft of this nature had something to do with her disappearance, though it's impossible to know for sure.
"There are many possibilities as to why the adult female has not been seen for the past month," Coster says. "She was quickly replaced with a four-year-old sub-adult female. [That bird] was recently seen mating with the resident male."
Bacci adds that bald eagles will sometimes also steal placenta off newborn sea-lion pups, or scavenge the carcasses of any youngsters that don't make it. Even in those instances, she has not witnessed any kind of attack on the birds.
"A newborn pup that dies is valiantly guarded by its mom," she says. "Only after she finally gives up [and vacates the area], will an eagle move in along with the turkey vultures."
"I think the story goes that Benjamin Franklin questioned whether we should have a thief and bully as our national symbol," jokes Coster.
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