An endangered Pacific Northwest orca that made global headlines in 2018 for carrying her dead calf for over two weeks is doing so once again following the death of her new calf, in another sign of grief over lost offspring, researchers said.

The mother orca, known as Tahlequah or J35, has been seen carrying the body of the deceased female calf since Wednesday, the Washington state-based Center for Whale Research said in a Facebook post.

“The entire team at the Center for Whale Research is deeply saddened by this news and we will continue to provide updates when we can,” the post said.

In 2018, researchers observed J35 pushing her dead calf along for 17 days, propping it up for more than 1,000 miles (1,600 kilometers). The calf had died shortly after it was born, and the mother and her closely knit pod of whales were seen taking turns carrying the dead body.

The research center said roughly two weeks ago that it had been made aware of the new calf. But on Christmas Eve, it said it was concerned about the calf’s health based on its behavior and that of its mother.

By New Year’s Day, officials with the National Oceanic and Atmospheric Administration were able to confirm that J35 was carrying her calf’s dead body, said Brad Hanson, a research scientist with the federal agency.

Hanson, who was able to observe her behavior from a boat on Wednesday, said J35 was draping the dead calf across her snout or on top of her head, and that she appeared to dive for it when it sank from the surface. He said the calf was only alive for a “handful of days.”

“I think it’s fair to say that she is grieving or mourning,” Joe Gaydos, science director of SeaDoc at the University of California, Davis, said of J35. Similar behavior can also be seen in other socially cohesive animals with relatively long life spans, such as primates and dolphins, he added.

Calf mortality is high: Only about 1 in 5 orca pregnancies result in a calf that lives to its first birthday, according to the Center for Whale Research. The center’s research director, Michael Weiss, estimated that only 50% of orca calves survive their first year.

The center described the death of J35’s calf as particularly devastating — not only because she could have eventually grown to give birth and bolster the struggling population, but because J35 has now lost two out of four documented calves.

The population of southern resident killer whales — three pods of fish-eating orcas that frequent the waters between Washington state and British Columbia — has struggled for decades, with only 73 remaining. They must contend with a dearth of their preferred prey, Chinook salmon, as well as pollution and vessel noise, which hinders their hunting. Researchers have warned they are on the brink of extinction.

Other southern resident orcas have been observed carrying dead calves, Weiss said, “but certainly not for as long as J35 carried her calf in 2018.”

There was some good news for the J pod, however: another new calf, J62, was observed alive by officials and scientists.

Southern resident orcas are endangered, and distinct from other killer whales because they eat salmon rather than marine mammals. Individual whales are identified by unique markings or variations in their fin shapes, and each whale is given a number and name.

Traveling together in matrilineal groups, the orcas at times can be seen breaching around Puget Sound, even against the backdrop of the downtown Seattle skyline.