Planet Earth

Horrible Gulls Are Eating Baby Whales Alive

InkfishBy Elizabeth PrestonNov 20, 2015 7:45 PM

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Yes, it's important not to anthropomorphize other species or impose our values on them—but sometimes animals are just horrible. For example, kelp gulls. A few decades ago the birds in one part of Argentina realized that for a tasty snack, they could tear flesh from the backs of whales when they came up for air. Eventually the whales learned to protect themselves somewhat from the gulls. But now the gulls have shifted their attention to the whales' babies, and might be killing them. Kelp gulls (Larus dominicanus) first got a taste for whale flesh in the 1970s. They began pulling pieces of dried-out skin from the backs of southern right whales (Eubalaena australis) while the whales were relaxing at the water's surface at Península Valdés, Argentina. This is a calving ground, where mother whales travel to have their young. The pairs stay here for a few months, nursing and swimming together, before they migrate to their feeding grounds. The gull attacks have escalated over time. Birds now gash the whales over and over with their beaks, opening holes and then gouging deeper into their skin and blubber. They sometimes chase the whales while they swim, waiting for them to come up for air so they can attack again. Carina Marón, a scientist at the Instituto de Conservación de Ballenas in Buenos Aires, Argentina, and her colleagues recently studied aerial photographs of this whale population taken between 1974 and 2011. They also looked at pictures of dead calves that had stranded between 2003 and 2011. At least 626 calves have died here since 2003, and the researchers wanted to know whether they could blame the gulls. Photos from the 1970s showed almost no whales with wounds from the birds. By the 1980s, more than a third of mother-calf pairs had visible wounds. In the 1990s, that number rose to 84%. And in the 2000s, 99% of mother-calf pairs had gull wounds. These whales used to spend as much as an hour at a time resting at the ocean's surface. But since the gull attacks started, they changed their habits. Now when they come up for air, they may keep their backs underwater by angling their bodies or arching their spines (what one scientist called "crocodiling"). But calves, being less experienced with the bitey ways of the world—and possibly less agile—don't use these tricks as often. That may be why gulls are increasingly targeting baby whales. The researchers saw that wounds on the backs of calves had increased over the past decades, relative to the wounds on their mothers. A typical calf in the 2000s bore nine visible gouges from gulls. Plenty of dead whale calves had gull wounds too. Yet the scientists couldn't prove that gulls had killed them. Gull wounds on dead calves increased overall between 2003 and 2011, but there was no difference between wound frequency in years when only a few calves died and years with many calf deaths. Still, being literally eaten alive by birds is bad for whales. The wounds could cause dehydration, make it harder for whales to regulate their body temperature, and drain their energy while they're healing. Mother-calf pairs that are under attack from gulls spend less time nursing, as well as less time resting or playing. They have to spend more of their time and energy fleeing their attackers. The researchers think other factors may be involved in the high numbers of baby whale deaths they've seen here lately. But the gulls are probably contributing. And, though it wouldn't be scientific to say so, the gulls are jerks.

Image: by Sandi (via Flickr). This is a right whale in Patagonia; as far as I know the birds are not attacking it.

Marón CF, Beltramino L, Di Martino M, Chirife A, Seger J, Uhart M, Sironi M, & Rowntree VJ (2015). Increased Wounding of Southern Right Whale (Eubalaena australis) Calves by Kelp Gulls (Larus dominicanus) at Península Valdés, Argentina. PloS one, 10 (10) PMID: 26488493

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