Persistent marine heat waves lead to massive seabird die-offs months later, research finds.

New study uses data collected by coastal residents along beaches from central California to Alaska to understand how seabirds have fared in recent decades. The paper appears in the journal Marine Ecology Progress Series.

“This is truly a global data set that asked a global-sized question: Does a warming world significantly impact marine birds, among the top predators in the nearshore marine environment?” says coauthor Julia Parrish, a professor of aquatic and fishery sciences at the University of Washington and executive director of the Coastal Observation and Seabird Survey Team, known as COASST.

“We find a dramatic delayed effect,” she says. “A warmer ocean, and certainly a suddenly warmer ocean as happens during an El Niño or a marine heat wave, will result in the death of hundreds of thousands to millions of marine birds within one to six months of the temperature increase.”

Marine heat waves have only recently gained attention. They include the unusually warm ocean surface off the Pacific Northwest nicknamed “the blob” that persisted from 2014-2016, as well as prolonged El Niño events and warmer oceans in Alaska associated with retreating sea ice.

The team’s previous research linked recent ocean warming to individual die-offs among seabirds, including common murres, Cassin’s auklets, and tufted puffins. This study takes a broader approach.

“Rather than track the specific numbers of any one species, this study measures the magnitude of mortality events, regardless of seabird species, above long-term normal,” Parrish says. “We asked: What rate are carcasses washing in, over what portion of coastline, and for how many months? Larger-magnitude events are those that push up all these measures.”

The study used surveys of beach-cast birds from 1993 to 2021 between central California and Alaska. Truly massive mortality events, with death tolls most likely exceeding a quarter million birds, occurred roughly once per decade. But between 2014 and 2019, five events met this mortality threshold.

“This is unprecedented. This type of massive die-off can be compared to a catastrophic storm that we would usually expect once per decade; they happen, causing massive damage, but usually there is enough time for areas to recover,” says lead author Timothy Jones, a research scientist in aquatic and fishery sciences. “From 2014 to 2019, the die-offs were not only some of the largest ever documented, but they kept happening year after year—like a catastrophic storm hitting without fail every year.”

Analysis shows that these extraordinary die-offs were statistically linked to persistently warmer conditions in the Northeast Pacific in the preceding months. Some birds, including murres, puffins, auklets, and shearwaters, suffered much more than others.

Read the full article about marine heat waves by Hannah Hickey at Futurity.