From Science is Awesome
A recent study found that African elephants are less stressed inside Serengeti National Park. The study tested the amount of the stress hormone gluccorticoid in the elephants dung, and found that elephants inside the protected park had were significantly less stressed.
This may seem obvious, but Serengeti National Park has no fences and the elephants are free to come and go as they please. There were far more elephants inside the park than outside, which suggests that they are aware of which areas are safe and which are not and that they actively avoid human interaction by not leaving the park.
More info: http://bbc.in/UHVtDh