Sinking into steamy hot springs, the giant rodents of Izu Shaboten Koen flick their ears and close their eyes against the camera clicks of fascinated onlookers, drifting into a hazy midday nap.

They might not know it, but the five capybaras are the star attraction at the zoo some two hours by train south of Tokyo.

Zookeepers are banking on the tourism appeal of the world's largest rodents to cash in on the fortuitous coincidence of Japan hosting the Olympics in the Chinese Zodiac's Year of the Rat.