All these variables require knowledge of biology and field ethics. Be sure you know what the rules are when you're in a state or national park.
Guidelines are available at ranger stations and visitor information centers.
For other locations, it may be helpful to consult a professional photography association to get an idea of what's considered ethical. There are also a number of excellent seminars both in the field and in a classroom setting that will help you in this area while fine-tuning your technical abilities and aesthetic sense. Knowing the animals you're photographing is also critical. There are many good resources for this information both on the net and at your local bookstore. A related issue is knowing about other animals in the vicinity that you may potentially see while looking for your subject.