Researchers spotted Tahlequah the killer whale swimming with her new calf, J61, on Dec. 20. The baby whale died a little over a week later

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.

Tahlequah, an orca that carried her dead calf for 17 days and more than 1,000 miles in 2018, lost another calf recently and is grieving the death in a similar way.