科学美国人60秒:Baby Whales Pecked to Death by Gulls

Gulls. You may have noticed that gulls can be pretty aggressive when it comes to grabbing food. But that behavior is more intense than you may know. Some kelp gulls snack on baby whales. Live baby whales.

In the early 1970s, only a handful of southern right whales were fed upon by kelp gulls off the coast of Argentina’s Peninsula Valdez. Back then just two percent of calves every year had to suffer at the beaks of the gulls, along with some of their mothers.

But now, 99% of the calves have to contend with hungry gulls driving their hooked beaks deep into their backs, ripping out chunks of skin and flesh and blubber, and gobbling it up. The finding is in the journal PLOS ONE. [Carina F. Marón et al, Increased Wounding of Southern Right Whale (Eubalaena australis) Calves by Kelp Gulls (Larus dominicanus) at Península Valdés, Argentina]

“Each gull has its own whale and it protects it.” University of Utah Biologist Victoria Rowntree. “Or maybe two gulls will have its own whale, and they’ll chase off any gulls that come in. And they just sit in the water waiting for the whale to surface again…They’re relentless.”

Adult whales have learned to arch their backs when they surface to breathe, keeping most of their body away from the hungry gulls. But the newborns can’t do that.

“You can see the mothers getting so annoyed…when finally she’s been able to sleep, and she hasn’t arched her back, and she is isn’t horizontal to the surface, and her calf is sleeping next to her and then a gull comes along and BAMMO…I think the study I did in 1998 showed it took 30 minutes for them to return to normal behavior and not do this avoidance behavior.”

More than 600 calves died between 2003 and 2014. Some years at least a fifth of all newborns perished. Researchers wonder if the gulls might be, if not responsible, then at least contributing to the pattern. Rowntree looked at whether the dead calves had more gull-inflicted lesions than those that survived, but she found that all of the youngsters get harassed.

It’s not that the gulls are evil, of course. They eat to survive. The challenge for these researchers is to come up with ways of protecting the whales, without simply wiping out the gulls.

—Jason Goldman