The long list of non-human species where females reign supreme when it comes to choosing a mate is getting a new entry: the capybara. Scientists have just discovered prevailing female choice in what was once thought to be a male-dominated mating system. 

The capybara, Hydrochoerus hydrochaeris, is a semiaquatic rodent that can weigh up to 200 lbs. It has long been known for its mating system that prioritizes male access to large groups of females (like a harem, of sorts) over female preference. This new finding upends what scientists previously thought.  

To figure this out, three researchers, led by biologist Miguel A Bedoya-Pérez, packed their bags and set out for Venezuela during the mating season. The three observed capybaras at Hato El Cedral, a massive cattle ranch found in the country's Llanos (huge grasslands that experience intermittent flooding). 

Due to the previously mentioned semiaquatic ecology of the capybara, the researchers couldn’t use traditional methods of capture to collect data on the capybaras. Instead, they chose the next best thing, riding horseback and lassoing the giant rodents.  

After tagging 26 individual capybaras, the team observed the groups. They watched female behavior very carefully over several months, noting when they were cooperative to mating advances and when they avoided them.

They found that females rejected dominant male capybaras' sexual advances just 1.8% of the time,  but rejected subordinate males 41.7% of the time. This discovery has shed the first rays of light on cryptic female choice in the capybara world.