Seagulls have developed a hunting strategy never before seen in the animal world—eating the eyeballs of live seal pups, a new study says.
During the past 15 years, scientists have logged around 500 instances of kelp gulls (Larus dominicanus) attacking and attempting to eat the eyeballs of newborn Cape fur seals (Arctocephalus pusillus pusillus) in Namibia’s coastal Dorob National Park (map).
Since blinded seals can't find help from other seals and easily succumb to more attacks, the birds have discovered removing eyeballs is an especially efficient way to get a meal.
The behavior seems to be entirely new to science—if a little tough to stomach, says study lead author Austin Gallagher, a postdoctoral researcher at Carleton University in Ottawa, Canada. (Also see "Gulls Be Gone: 10 Ways to Get Rid of Pesky Birds.")
“It is not a pleasant behavior to observe, as the seals completely freak out and make a lot of noise,” says Gallagher, whose study was published August 14 in the African Journal of Marine Science.
"Cruel Way to Go"
Life for a Cape fur seal pup is pretty tough to begin with.
For one, the babies can’t swim and have to rely on their mother’s milk, says Michelle Jewell, a behavioral ecologist at the Royal Netherlands Institute for Sea Research who wasn't involved in the new research.
To supply that milk, the mother seals must occasionally go hunt fish, leaving the pups alone at the colony for several days. The unprotected pups might then fall prey to land predators such as lions and hyenas—and now, seagulls.
In the study, kelp gulls were successful in plucking out eyeballs in roughly 50 percent of observed attacks.
“A blind seal cannot forage, cannot find mom, and will get attacked by other gulls,” says Gallagher. (Also see "Baby Harp Seals Being Drowned, Crushed Amid Melting Ice.")
In many cases, once a gull pecks out the eyeballs, other kelp gulls join in and begin to eat the seal’s exposed areas, such as its underbelly and genitals, the scientists observed.
“It’s a cruel way to go,” says Gallagher. But from the gull’s point of view, it’s a “beautifully strategic attack.”
But why are gulls just now targeting seal eyeballs?
Gallagher believes it's likely a result of an increase in Cape fur seal populations—essentially, the birds are taking advantage of a newly abundant food source.
In the winter months, between 20,000 and 80,000 of the pinnipeds flock to Namibia’s coasts to mate and raise young. This dramatic population increase from just around a hundred seals in 1998 is due to the species' natural boom-and-bust cycles, the study says.
Seagulls are also very quick learners.
“Once one gull figures out a fast food meal like Cape fur seal eyeballs, other gulls observe and quickly learn the new feeding behavior,” Jewell says. (Also see "Cute Killers? Gray Seals Maul, Suffocate Seals and Porpoises, Studies Say.")
Not to mention "the eyes are soft targets, and a good source of both fluid and protein,” adds Craig Harms, a veterinary medicine expert at North Carolina State University who wasn't involved in the new research.
As a responder for the U.S. Marine Mammal Health and Stranding Response Program, Harms has seen firsthand the damage gulls can do.
“Gulls particularly like to peck at and eat the jaw fats of beached harbor porpoises, dead or alive,” says Harms.
“It's not surprising," he says, "that they would find a similar source of fresh food that is not good at defending itself."