December 11, 2023

The matriarchal structure of orca society is known, with female orcas living up to 90 years and playing a vital role in passing knowledge to young animals. previous studies Why these females lived so long after they stopped reproducing – an average of 22 years – suggests that they were meant to play an “older” role in society, passing on culture, language, etc. to the youngest group members.

Now, new insights show that postmenopausal southern resident killer whales (killer whale) play a key role in preventing brawling among young male calves in the herd.

Lead author Charlie Grimes, from the Animal Behavior Research Center at the University of Exeter, said: “We were fascinated to discover this specific benefit for males and post-fertile mothers.”

Researchers analyzed nearly 7,000 images of orcas living off the U.S. Pacific coast and found that males with postmenopausal mothers or grandmothers cared for them had significantly fewer tooth rake marks, the “battle scars” other orcas leave in battle.

“Tooth rake marks are an indicator of physical social interaction in killer whales, often acquired through fighting or rough play,” Grimes said. “These males had 35 percent fewer tooth marks than other males.”

Men without mothers had 45 percent more tooth rake marks.

While scientists aren’t sure how female orcas intervene in juvenile conflict—perhaps through complex vocalizations—the intervention is unlikely to be physical, since older orcas don’t have a higher rate of scarring than younger ones.

Furthermore, mother orca mothers who were still breeding did not exhibit this protective helicopter parenting style, suggesting that this is a specific behavior that belongs to the life stage of postmenopausal orcas.

“We can’t be sure why this changes after menopause, but one possibility is that stopping reproduction frees up the time and energy for mothers to protect their sons,” Grimes said.

As for the daughters? Don’t worry. Because males “inbreed” with several females in other pods, there is an evolutionary need to ensure that genes are passed on, the researchers note. Older bodyguards are useful as there is more competition among younger males. Injuries from rakes can lead to infection or something more serious.

“Older female whales may use their experience to help their sons cope with social encounters with other whales,” said Darren Croft, a professor at the University of Exeter. “They have previous experience with individuals in other groups and understand their behaviour, so they can steer their sons away from potentially dangerous interactions.

“When fights are likely to occur, mothers may also step in,” he added.

The study was published in the journal modern biology.

source: University of Exeter