Anyone who’s had a sandwich stolen out of their hands by a gull at the beach knows firsthand how bold and aggressive these birds can be in their quest for food. But there are gulls that do far worse than steal a sandwich. Consider the kelp gulls and dolphin gulls on Guafo Island in the Patagonian region of Chile. They actually can wound South American fur seal pups as these birds dive to get the pups’ feces — straight from the source. That’s the finding of a new study.
Gulls “are very opportunistic,” explains Mauricio Seguel. He’s a veterinary pathologist at the University of Georgia in Athens. “That’s one of the things that is so amazing about these birds. They can adapt so easily to so many different environments.”
Kelp and dolphin gulls on Guafo Island eat a varied diet, Sequel says. They dine on shellfish plucked from the ocean at low tide. They crack into sea urchins by dropping them from heights onto the rocks. They’ll steal fish or crabs out of the claws of marine otters. But a big portion of their diet comes from cleaning up after the island’s fur seal colony. The gulls eat placentas left behind after pups are born. If newborns die, they eat them as well.
Researchers have been trying to learn more about the seals’ biology and how changes in the ocean might affect them. To do that, they’ve monitored one fur seal colony since 2003. Five years into this study, the scientists started finding wounds in the perineal area — near the anus — of some pups they had marked for study. It wasn’t many pups. Just 5 to 9 percent of those they sampled each year from 2012 to 2017. And some of the wounds were infected.
Researchers caught the culprits in 2015 and 2017. That’s when they spotted kelp gulls and dolphin gulls picking at the butts of young seals. Each pup was around two-months old. The birds were swooping in to eat their feces.
Hookworms often infect fur-seal pups in this colony. These parasites infect the gut, causing bloody diarrhea. They also are responsible for killing about a fifth of the pups each year, Seguel notes. The poop of infected pups is full of the expelled hookworms. And this was what drew the gulls. The gulls only went after the poop of infected pups. In fact, when the researchers treated 30 pups with a drug to kill the parasites, the gulls left all but one of them alone.
The gulls don’t mean to harm the pups. Yet Seguel and his colleagues found signs that some pups had developed whole-body infections, likely due to wounds caused by the butt-pecking gulls. They reported this July 26 in Royal Society Open Science.
The researchers don’t think that the gulls are having a big impact on the fur seal population. But that could change, Seguel warns.
An example comes from gulls that attack a different species. Some kelp gulls are known to pick at skin and blubber on the backs of Southern right whales swimming off the coast of Argentina. Scientists suspect that these wounds kill many calves of this species. The birds weren’t a big problem for the whales, Seguel notes, until an increase in fishing and urban wastes drove an increase in the gull population.
Gulls are very adaptable and easily affected by human activities. It’s another reason, Seguel says, that people should be careful. Our activities can have long-lasting, unforeseen impacts on nature.