There is one simple statement that comes to mind when it comes to wildlife photography.
“The well-being of the subject must come before the photograph”
In this digital age it has become relatively easy to fund high quality telephoto lenses, and camera bodies for wildlife photography. However with this comes a responsibility to understand nature, the biology and the behaviour of wild animals. Unfortunately this side is often neglected. Below is a list of resources designed to help steer photographers in the right direction with regards to ethical wildlife photography.
I firmly believe that spending time researching your subject will not only allow you to take photographs without disturbing the animals, but also allow you to ultimately produce a better body of work.