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.
aggressive (n. aggressiveness) Quick to fight or argue, or forceful in making efforts to succeed or win.
anus The opening at the end of an animal's digestive system through which solid waste leaves the body.
behavior The way something, often a person or other organism, acts towards others, or conducts itself.
biology The study of living things. The scientists who study them are known as biologists.
blubber The thick layer of fat under a marine mammal’s skin that helps it stay warm even in cold waters. In the past, whalers would boil whale blubber to extract oil, which had many industrial uses.
colleague Someone who works with another; a co-worker or team member.
diarrhea (adj. diarrheal) Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
feces A body's solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.
gull A family of long-winged and relatively thick-bodied shoreline birds. Most are gray and white with webbed feet. They tend to be very vocal.
hookworm A type of bloodsucking nematode (small worm) that lives within the intestines of people and other animals. With hooklike mouthparts, it attaches to the wall of the gut. This parasite punctures blood vessels there to reach the blood it seeks.
infection A disease that can spread from one organism to another. It’s usually caused by some type of germ.
kelp A type of large seaweed that is usually a type of brown algae. They grow underwater and form large forests, providing habitat for many organisms. Some kelp forests are so large they can be seen from space.
marine Having to do with the ocean world or environment.
parasite An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.
pathologist Someone who studies disease and how it affects people or other infected organisms.
placenta A sac that connects the embryo to the uterus in most mammals. The placenta supplies oxygen and nutrients to the developing embryo. It also takes away waste.
population (in biology) A group of individuals from the same species that lives in the same area.
pup A term given to the young of many animals, from dogs and mice to seals.
sea An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
urban Of or related to cities, especially densely populated ones or regions where lots of traffic and industrial activity occurs. The development or buildup of urban areas is a phenomenon known as urbanization.
urchin Small, spine-covered sea animals without eyes or limbs which are related to sand dollars and starfish.
veterinary Having to do with animal medicine or health care.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
whale A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.
Journal: M. Seguel et al. Kelp and dolphin gulls cause perineal wounds in South American fur seal pups (Arctocephalus australis) at Guafo Island, Chilean Patagonia. Royal Society Open Science. Published online July 26, 2017. doi: 10.1098/rsos.170638.
Journal: C. F. Marón et al. Increased wounding of southern right whale (Eubalaena australis) calves by kelp gulls (Larus dominicanus) at Península Valdés, Argentina. PLOS ONE. Published online October 21, 2015. doi:10.1371/journal.pone.0139291.