Elephants are being pushed into smaller and smaller spaces. And increasingly, they're pushing back.

According to the National Geographic Channel documentary Elephant Rage, some 500 people are killed by elephant attacks each year. Such attacks are becoming increasingly common, researchers say.

"I do think that elephants are becoming more aggressive towards humans in very compressed areas where they are being shot at and harassed," said Caitlin O'Connell-Rodwell, a biologist at Stanford University in Palo Alto, California.

"It is a difficult dilemma in areas where elephant habitat is shrinking and the human population is increasing such that poor farmers have little choice but to expand their farms to make ends meet," she said in a telephone interview from a Namibian field camp.

Elephants are the