Rhinoceroses vary in size depending on the species: The largest is the white rhino, which weighs between 4,000-6,000 pounds (1,800 – 2,700 kilograms). The Javan rhino is the smallest, weighing in at about 1,300 – 2,000 pounds. Because of their huge size, strength and aggressiveness when attacked, rhinoceroses are not often hunted by animals other than humans, although young or sick rhinos are occasionally killed by lions or crocodiles. Rhinoceros skin is very thick, up to 1.5 cm. It is tough but also quite sensitive to sunburn and insect bites. They often cover themselves in mud to protect their skin from insects and the sun. Rhinos eat grasses, leaves, and the shoots of bushes and trees. Exactly what rhinos eat can depend on the species and specialization of its lip shape. Rhinos have poor eyesight but excellent sense of smell and hearing. Female rhinos gestate their young for about 15-16 months and give birth to a calf every two to three years. Male rhinos tend to be solitary animals, while females and young rhinos are more social, depending on the species.