Like your pet kitty relaxing at home, cheetahs and mountain lions exert as little energy as possible and rest up for bursts of activity, two new studies reveal Thursday.

Perhaps more surprising, though, cheetahs spend only about as much energy in a day as a person does, the scientists found.

The studies are the first to calculate the actual, minute-by-minute costs of being a big, wild carnivore—information sorely needed by scientists working to save big cats, says ecologist Terrie Williams of the University of California, Santa Cruz, who led the mountain lion study. (Read "Cheetahs on the Edge" in National Geographic magazine.)

As people alter wild habitats, they may throw this delicate balance off-kilter and make it harder