Anyone who’s had their chips 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.
For gulls in Chilean Patagonia, seal pup poop laced with parasitic hookworms is a tasty treat. But the eager birds are snapping up their meals just a little too near to the pups, to the detriment of the seals' tender rear ends, scientists reported in a recent edition of Royal Society Open Science.
Gulls “are very opportunistic,” explains Mauricio Seguel. He’s a veterinary pathologist at the University of Georgia in Athens. During routine exams of the South American fur seal pups (Arctocephalus australis) living on Guafo Island, researchers were puzzled by unusual wounds they found in the young animals' perineal area — around the anus.
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.
Initially, the scientists wondered if the lesions on the pups' rears were caused by a viral or bacterial disease. However observations later revealed that gulls feeding on the pups' poo approached too close for comfort, jabbing their sharp beaks into the seals' bottoms, and creating gouges that sometimes led to serious infections, according to a new study.
Guafo Island Research Group - This is a presentation on the Guafo Island Research Group and the critical importance of preserving this unique research site. Guafo Island is a remote island in Northern Chilean Patagonia which is home to the largest fur seal rookery in the pacific. Guafo Island provides
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.
Kelp gulls (Larus dominicanus) and dolphin gulls (Leucophaeus scoresbii) live alongside the seals on Guafo Island, and feed on seal feces produced by both adults and pups. The seal population in this area is known to be infested with hookworms, a common parasite in fur seals, and while adult seals mostly harbor hookworm larvae, the pups play host to hookworms in their adult forms, which they often expel in their feces.
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.
Source: Royal Society Open Science