Dominant Female Mongooses Bully to the Max

THE GIST:

• Female bullying is extreme among female banded mongooses.
• Mongoose bullies torture pregnant relatives until victims are forced to leave.
• Physical eviction of subordinate females can benefit the offspring of dominant females.

Female bullies are common throughout the animal kingdom, but few are as brutal as female banded mongooses that, according to a new study, torture pregnant relatives until these victims are often traumatized enough to self-abort their litters.

The findings, published in the latest Proceedings of the Royal Society B, suggest that female bullying may frequently be tied to reproductive cycles and can benefit the aggressors if they take physical action.

Women in groups often enter estrus at around the same time, which in mongooses and our closest living animal relatives, chimpanzees, is an evolved phenomenon that helps to prevent infanticide "because females may risk inadvertently killing their own young if they attempt to kill the offspring of other females," according to lead author Michael Cant and his team.

But peaceful group living among female banded mongooses falls apart when dominant, older females decide to kick subordinates out.

"Eviction events start suddenly when older dominant females turn on other females and start to repeatedly chase, scratch and bite them," Cant told Discovery News. "Other group members, including males and subadults also join in, chasing and attacking the victims."

The process continues for one to two days, with victims attempting to return home, only to be attacked more.

WATCH VIDEO: Animal Planet: An adorable litter of banded mongoose pups takes its first look at the outside world.

Related Links:

• Monkeys Display Verbal Skills
• Animal Mating Secrets Revealed
• HowStuffWorks.com: Mongoose
• Termites Eavesdrop to Avoid Bullies

"Evictees can suffer quite nasty injuries and are often bleeding and limping by the end of the eviction," said Cant, a research fellow at the Center for Ecology and Conservation, University of Exeter in Cornwall.

He added, "The process of being evicted is probably extremely stressful and we think that this physiological stress may be the mechanism that triggers spontaneous abortion."

He and his team documented the behavior while studying 1400 banded mongooses living in 20 groups in and around Mweya Peninsula, Uganda.

Bullying breaks up the family home, but is a maintained behavior because it benefits the pups of dominant females, the scientists believe. These older dominant individuals tend to leave very young females alone, but often target "middle-aged" females between the ages of 2 and 5.

"We have shown that the survival rate of dominant females' pups between the ages of 1 month and 3 months declines with the number of subordinate breeders," Cant said. "This is likely due to competition for limited resources and access to good helpers -- 'escorts.'"

He explained that escorts "are adult helpers that form exclusive one-on-one relationships with particular pups, and protect and provision pups until they become nutritionally independent at 3 months of age."

As for the kicked-out middle-aged females, those that abort their litters are sometimes accepted back into the group. Mongooses that cannot rejoin sometimes form new groups with other bullied females and subordinate males that have left their own groups voluntarily.

Such intense competition among females could even help to explain why women cease reproduction midway through life, which isn't always the case for other animals. Female elephants, for example, breed into their 60's, while baleen whales can reproduce into their 90's.

In a separate study, Cant and co-author Rufus Johnstone found that "the rapid [aging] of the female reproductive system coincides with the age at which, in natural fertility populations, women are expected to encounter reproductive overlap between generations."

Menopause may then help to prevent mating competitiveness that could lead to harmful fights among women.