It’s not uncommon for human parents to sacrifice for their children, but scientists have now observed orca doing the same thing.

A study in the journal Current Biology found it’s “reproductively costly” for female orcas who care for their adult sons.

One example is K35, a killer whale profiled by NPR. The whale gave birth to a son 20 years ago and still helps feed him.

(Video courtesy of BBC News)

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“These two have an extremely close social relationship,” Michael Weiss, the research director at the Center for Whale Research, told NPR.

Weiss said the close relationship appears to have stopped K35 from producing more offspring.

He noted that other whales around the same age have gone on to reproduce.

(Video courtesy of TED-Ed)

“They’ve produced three or four offspring,” Weiss told NPR.

There’s concern that the practice could impact the survival of the southern resident killer whale. The study notes that there are believed to be less than 70 alive today. Researchers worry that if more female orcas provide long-term care for sons and do not reproduce, the population will drop.