Mr. Hanson said on Thursday that he did not know why the female calf, who lived for a few days during the last weeks of December, had died. The mother, one of only a few dozen of its type of orca, was seen carrying the dead female calf on Wednesday, though might have been doing so for longer.

The calf was born Dec. 24. Observing researchers noted unusual unspecified behaviors by mother and calf that led them to worry for the young whale's health.

Tahlequah, an orca whale who carried her dead calf for 17 days in 2018, is grieving another loss. On Jan. 3, researchers confirmed that Tahlequah lost another calf and is once again carrying her baby's body through the ocean,