Biologists have long been trying to figure out why certain species go through menopause while others do not, but a recent study on killer whales sheds light into why orcas undergo menopause.

Earlier studies had hinted that whales, in particular, may undergo menopause so they remain focused on the survival of their existing offspring rather than giving birth to more baby whales. The same group that made this bold assessment are now claiming that they may have figured another important reason why killer whales menopause.

Published in the journal Current Biology, the study conducted by behavioral ecologist Darren Croft from the University of Exeter and his fellow researchers analyzed the data on the killer whales in the Pacific Northwest.

The data, collected over 43 years, included the births of 525 calves. The researchers noticed that when older females and their daughter who live with them deliver new calves simultaneously, the calves of the older females are 200% more likely to die in their first 15-years. However, the survival rate of the calves is much more higher if there was no other reproducing daughter.

“When mothers and daughters co-breed, the mortality hazard of calves from older-generation females is 1.7 times that of calves from younger-generation females,” the researchers wrote.

The researchers noted that the findings certainly do not indicate that older whales are less capable of raising their calves compared to the younger mothers. Instead, the competition between older and younger females over resources may have a lot to do with the phenomenon.

Croft and his colleagues noted that in any conflict over resources, older mothers were more likely to lose against their young, reproducing daughters. According to them, that could explain why the offspring of the younger females fared better comparatively. They further explained that the competition may mostly involve food as older females are probably required to share their food more with others around them, essentially meaning that younger females end up having more food that they can give to their own offspring.

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