The shipment arrived airfreight: 47 seabird carcasses collected by the Bering Strait villagers of Shishmaref.

Marine biologist Gay Sheffield drove to the airport on an August day to pick up the grisly cargo and bring it back to a laboratory just off the main street of this northwest Alaska town.

Inside a cardboard box, Sheffield found mostly shearwaters, slender birds with narrow wings — also kittiwakes, crested auklets, thick-billed murres, a cormorant and a horned puffin. Most were painfully skinny, bones protruding like knife-edged ridges.

“They starved to death,” Sheffield said. “Why?”

The birds should have been able to fatten on small fish, krill and other food that typically abound in the northern Bering Sea, a body of water so rich in marine life that gray whales, after they winter off Mexico, swim more than 5,000 miles north to feed here each summer.

But as climate change warms the die-offs of seabirds and marine mammals have been on the rise. The grim tally includes a nearly fivefold increase in ice-seal carcasses spotted on shore, strandings of emaciated gray whales, and near the St. Lawrence Island village of Savoonga, a discouraging spectacle: auklets abandoning seaside nests as their chicks succumb to hunger.

“I came upon a baby auklet on the beach. It was getting weak, dying slowly and suffering,” said David Akeya, a Savoonga resident. “I had to end its life.”

The animal die-offs offer the world a stark example of the perils of rising ocean temperatures, which already are upending parts of the Bering Sea ecosystem as climate change — driven by greenhouse-gas pollution from fossil fuels — unfolds in Alaska at a breakneck pace. For the past two years, the winter ice has largely disappeared, and this fall, ice formation in some of the northern waters has been at historic lows.

These are startling developments for those who live along the shores and for the Seattle-based fishermen whose fortunes are tied to the Bering Sea harvests that are some of the biggest on the planet.

Federal and university scientists are trying to better understand why some birds and marine mammals have been unable to find enough food, and whether toxic algae blooms — increasing as the water warms — could have contributed or caused some of the die-offs.

The pace of the research frustrates Sheffield, an Alaska Sea Grant biologist who has worked in the northern part of the state for more than a quarter century. As the warming takes hold — raising some summer sea-bottom temperatures by more than 12 degrees in less than a decade — Sheffield has emerged as a front-line scientist traveling around the region to document death tolls and gather specimens for analysis. Along the way, she’s heard from Yup’ik and Iñupiat villagers who eat the seabirds and marine mammals, and — disturbed by what they were finding — began to gather samples from dead animals and airfreight them to Sheffield in Nome.

“It’s not an academic issue out here,” Sheffield said. “If you live here, it’s a real-world problem. It’s an immediate, stop, get an answer problem. It’s a food security and health problem … and people are very brave in taking action.”

The struggles of Alaska’s seabirds grabbed scientists’ attention in 2015, when hundreds of thousands of dead and dying common murres washed ashore along state’s south-central coast during a period of unusually warm water temperatures.

That Alaska seabird die-off was thought to be the biggest on record and could be devastating if repeated, according to a National Park Service publication. It was followed by a series of other die-offs.

Scientists have sent more than 220 seabird carcasses found along different parts of Alaska’s shoreline to a U.S. Geological Survey (USGS) laboratory in Madison, Wisconsin, for necropsies.

More than 80% of the birds were found to have died from a lack of food, according to Robert Dusek, a government biologist in Madison.

Why can’t the seabirds find a meal?

In some areas, the answer may be simple: a food shortage.

Many of these seabirds eat tiny shrimplike creatures such as krill and copepods, whose numbers — according to federal marine surveys — have declined as the water off Alaska has warmed.

Others, such as the murres, dine on small fish such as smelt, which in the northern Bering Sea have suffered a 98% population drop in eight years, according to federal surveys. And as seabirds search for these fish, they may face increased competition for their prime food sources from Pacific cod and pollock that — as the winter ice has faded — migrated here from waters farther south.

In surveys this year, northern Bering Sea pollock populations surged more than 50-fold compared to 2010, and the Pacific cod increased more than 14-fold.

“Things are out of whack. When you throw in multiple species of these predatory fish, it’s no surprise that we are going to have problems,” Sheffield said.

The seabird’s difficulties finding food were on painful display this summer near Savoonga, a St. Lawrence Island village in the northern Bering Sea, where a poster on the wall in the local tribal building urges people to not eat birds found dead along the beaches, to handle them with gloves and to report those locations to scientists in Nome or Anchorage.

During a monthlong visit last summer, biologist Alexis Will observed auklets diving into the water in search of copepods. She examined their vomit for signs of this key food but found they did not have much success in their foraging.

Exhausted birds washed up on the beach and died. Meanwhile, in the more than 30 nests Will surveyed, none of the baby chicks survived past two weeks, prompting the adults — first the least auklets and later the crested — to abandon the colony.

“Usually, there are ‘cheeps’ (from chicks) coming out of every single crevice,” Will recalled. “But it was just silent. It was kind of like you show up at a dance party and no one is there.”

As the winter ice has faded — and waters have warmed — seal deaths also have been on the rise.

During the past two years, 282 seal carcasses have been spotted on the northern Alaska’s shoreline, and a lack of food appeared to play a role in one major die-off Sheffield investigated.

In June 2018, she tallied 45 carcasses of bearded, ringed and spotted seals on a half-mile stretch near the village of Wales, north of Nome on the Seward Peninsula.

These were all ice seals, which during the winter and spring months depend on the frozen sea to help them find food, bear their young and escape predators. They were mostly pups and young adults, and during this summer season they should have been foraging for small fish and other marine life in coastal waters.

But many of those found in Wales had only thin layers of blubber over their ribs. Checking their stomachs, Sheffield wrote in a report that she found “no recognizable prey items,” only “sand, plastic debris, a pebble and a wood fragment.”

“I had never seen such a die-off,” Sheffield said.

Toxic algae produced by the warming Bering Sea poses another risk for mammals and birds.

The cysts of these algae have been found in surprising amounts on the ocean bottom in northern Alaska waters, according to Don Anderson, a researcher at the Woods Hole Oceanographic Institution, whose team mapped the cysts during a trip on the Coast Guard cutter Healy.

As ice recedes and water temperatures climb, the cysts unleash blooms, which in the years ahead are expected to become more intense and more widespread.

“You could see die-offs of whole groups of animals. This is the unknown,” said Kathi Lefebvre, a Seattle-based federal biologist who studies the effects of toxic algae on animals and humans.

The two most common strains — saxitoxin and domoic acid — attack the nervous system. In low amounts, they appear to cause no harm but at higher levels can cause illness or death.

Lefebvre was the lead scientist of a 2016 study that detected one or both of these harmful algae in 13 species of marine mammals. Walruses were found to have the highest concentrations — roughly the same levels of domoic acid that had triggered seizures in California sea lions in Pacific waters much farther south.

Two years later, in the summer of 2017, saxitoxin emerged as a suspect in the strange behavior of a walrus that pulled out on the northern Bering Sea island of Little Diomede. The great, tusked creature was fatigued and hung its head. Surprisingly, it was not spooked by the presence of villagers nearby.

The hunters who killed the walrus after observing it for 45 minutes were wary that something was wrong. They opted not to eat it, and — after a phone call to Sheffield — opened the intestines, scooped out a fecal sample and shipped it to her, and she forwarded it to a federal lab in Seattle.

The analysis showed saxitoxin concentrations more than four times higher than federal standards allow in seafood eaten by humans. Toxin levels likely would have been much lower in the muscle and blubber — but that assumption still requires further investigation, according to Lefebvre.

This was disturbing news back in Little Diomede. There, walrus is a staple food, and people may eat all parts, including organs, though hunters have long keenly observed the body conditions of marine mammals and don’t eat those that are sick. But the potential for a toxic algae had not been a consideration.

“We were astounded, said Francis Ozenna, tribal coordinator for the village of Little Diomede.

Toxic algae may have played a role in the deaths of 39 walruses that in the summer of 2017 washed up on the shores of Northwest Alaska. Analysis found moderate levels of saxitoxin in samples taken from some decaying bodies.

“There is no doubt that the toxins are a suspect,” Lefebvre said.

Algae toxins may be involved in some of the bird die-offs.

During the August cruise of the Coast cutter Guard Healy, scientists spotted dead birds, including in an area where the Woods Hole team detected high levels of an algae that can produce saxitoxin.

They collected more than 100 deep-water samples of clams, worms and krill, all of which are food for marine life. Tests by Lefebvre in Seattle showed two of the clams had levels of saxitoxin above the federal seafood safety limit. The rest had moderate levels of saxitoxin, according to Lefebvre.

Scientists also retrieved a very skinny short-tailed shearwater for analysis at the U.S. Geological Survey laboratory in Wisconsin. So far, the USGS scientists have looked for traces of saxitoxin in more than 100 dead Alaska seabirds. More than 30% tested positive, including many that were determined to have died from starvation.

This finding raises the possibility that some birds are disoriented and weakened by ingesting the toxins to the point where they can’t forage for food.

“That’s certainly a hypothesis we are considering,” said Dusek, the USGS biologist who conducted the testing.

With so many unanswered questions, Sheffield has wrestled with how to assess — and communicate — the risks posed by the die-offs.

She helped put together an Alaska Sea Grant publication that summarized the findings of saxitoxin in walruses, and urged villagers to be vigilant for odd walrus behavior. She presented timelines, maps and test results at community meetings in Little Diomede and other villages. And this summer in Nome, she organized a workshop on algae toxins that helped alert local health officials to the potential for human illness.

So far, there have been no confirmed cases of algae toxin illness among the native people of Northwest, Alaska, according to a state epidemiology official. But Sheffield is concerned about a lack of monitoring, so it’s hard to know just what is happening.

This summer, Sheffield spent a lot of time documenting the die-offs. She spent a long afternoon, her hands clad in blue plastic gloves, examining birds that came out of the box from Shishmaref. Each was put in a plastic bag, then put in a freezer so they could be shipped south for further analysis.

“We have a crisis. We’ve got to get answers.”