After analyzing thousands of documented sightings and aerial photographs collected from 1970 through 2017, the researchers found that the number of injuries sustained by young southern right whales in Península Valdés has increased around tenfold in the past two decades. Over that same time period, they have linked a decrease in calf survival with the severe injuries inflicted by the birds.

“The fact that gull harassment is causing population-level impacts on these whales is pretty surprising,” said Matthew Leslie, a conservation biologist with the U.S. Geological Survey who was not involved with the study.

Once on the brink of extinction, the southern right whale has recovered since hunting it was banned in 1935. However, as is the case for nearly all whales today, that recovery is threatened by declining food sources, regular entanglements in fishing gear and ship strikes.

“For these whales, it’s death by 1,000 cuts,” Dr. Leslie said, “and these gulls are adding one more cut.”

The scientists behind the study argue that humans are partially to blame for the Patagonian whales’ plight, pointing to poorly managed landfills and the waste created by fishing fleets, which increase the kelp gull population.

“By providing scientific evidence that gull attacks have an impact on whale survival, we hope that people can change attitudes and get more involved in improving waste management,” Dr. Sironi said.