Like HowStuffWorks on Facebook!

Orca Menopause May Be Related to Mother-Daughter Competition


A girl peers at a killer whale on display in SeaWorld's San Diego Park in 2006. The park announced in March that it will no longer breed the animals. Wolfgang Kaehler/LightRocket via Getty Images
A girl peers at a killer whale on display in SeaWorld's San Diego Park in 2006. The park announced in March that it will no longer breed the animals. Wolfgang Kaehler/LightRocket via Getty Images

As far as anyone can tell, we animals come here with a surprisingly few number of jobs. In order of importance, they are,

     1. Reproduce

     2. Stay alive long enough to reproduce

Reproduction is such a huge deal that biologists have long been confounded by the few animals that do the whole menopause thing. Wouldn't it make more sense to be able to have babies right up until the bitter end? The overwhelming majority of mammalian species do it this way — everybody, in fact, except humans and two whale species, killer whales being one.  

Female killer whales, or orcas, have a lifespan and lifecycle very similar to that of humans: they can become mothers starting in their early teens, and go through menopause in their 30s or 40s, although many females live into their 90s. Males, on the other hand, rarely make it past 50. A new study published in the journal Current Biology looks into the reasons behind why female orcas stop reproducing halfway through their lives — and finds it might have something to do with minimizing tension between mothers and daughters.

The team's previous research shows that in orca communities, older females are important leaders, helping their children find the best sources of food. But what's keeping these older ladies from having babies, just like their daughters and granddaughters? Earlier work by two of the study co-authors theorized that for humans, older women become more closely related to those around them as they age, and younger women tend to spend more effort competing to reproduce, and that because of this process older women end up investing more time in helping care for the children of the younger women rather than in competing with them.

In the most recent study, the researchers tested their hypothesis in killer whale communities, looking at 43 years' worth of demographic data for a group of wild resident orcas in the Pacific Northwest. They found that when older female orcas had babies at the same time as their daughters, their calves were 1.7 times more likely to die than those of their daughters.

"Our previous work shows how old females help, but not why they stop reproducing," says Dr. Darren Croft, a behavioral ecologist at the University of Exeter, in a press release. "Females of many species act as leaders in late life but continue to reproduce. Our new work provides a mechanism that can explain why old females stop [reproducing] — they lose out in reproductive competition with their daughters."

So, at least for killer whales, menopause seems to have evolved to serve an important social function: to maximize cooperation within groups while minimizing competition between generations of females.

Next the researchers want to use drones to examine the behavior of these whales:

"We want to understand how old and young females are behaving in ways that impact the survival of their calves," says Croft. "For example, who are individuals sharing food with and when are they sharing it? Who is doing the babysitting? By getting a bird's eye view, we will be able to transform our understanding of the social lives of these amazing animals."