Humans apparently aren't the only animals with a feminist movement. Female elephant seals from the South African sub-Antarctic Marion Island colony are protesting the system of hierarchy in their world the only way they know how — by taking to the water.

Normally, female southern elephant seals (Mirounga leonina) mate only when they are part of a dominant male's harem. The massive seals congregate on beaches, and males stake a claim to sometimes hundreds of females, in a system known as polygyny.

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Elephant seal bulls make Stanley from A Streetcar Named Desire seem like a nice guy. The big males bellow and battle for territory. Only the biggest and fiercest males can defend their harems. During the fights, however, males often kill females and their pups as they throw their weight around.

Males can grow up to 16 feet long (about 5 meters) and weigh 6,000 pounds (2,800 kilograms), but females are generally much smaller, tipping the scales at 1,650 pounds (750 kilograms) and measuring 10 to 12 feet (3 to 3.6 meters). That size difference means male elephant seals can easily overpower females.

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But Nico de Bruyn, a marine mammal ecologist at the University of Pretoria working with other South African and Australian researchers, has found that as many as half the females from the Marion Island colony are avoiding the harem system and the male bullying on the beaches. The message seems to be: If the males want to mate, they will have to do it in the water, where the females are on more equal terms.

"For a male, even if he is huge in comparison to the female — which they are — coercing a female is so much more difficult in the water because she has more options," de Bruyn said in an article in Inside Science.

The behavior has not been observed in other elephant seal populations.

"We have no evidence that it occurs in northern elephant seals. I'm not even sure how prevalent the observation is for southern elephant seals," said ecologist Daniel Costa of the University of California, Santa Cruz, who leads a tagging program for northern elephant seals in the Pacific.

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Elephant seals were nearly extinct at the end of the 19th century. Humans hunted them for their blubber until both species, the northern and southern elephant seals, were down to perhaps 100 individuals.

But humans stopped hunting the seals and their numbers recovered. Over the past 25 years, researchers have been tracking the Marion Island elephants seals. By studying where the creatures spend their time, de Bruyn and colleagues noticed that some females skipped mating seasons on the beach but still ended up pregnant.

The researchers believe that the females may have developed an alternative mating strategy that gives them more control over their mating choices. In their study, "Sex at sea: alternative mating system in an extremely polygynous mammal," published in the journal Animal Behavior, they suggest that female alternative mating strategies should be examined in other polygynous species.

"Traditional concentration on male strategies has hampered our understanding of mating systems, in assuming that females capitulate to these strategies," they write. "We suggest similar misinterpretations could occur in other polygynous species."

Indeed, there may be other feminist revolutions going on in the animal kingdom.

IMAGES 1 and 2: Two northern male elephant seals fight for dominance. (Wikimedia Commons)

IMAGE 3: Elephant seals mating. (Wikimedia Commons)