When someone says portrait photography most people think of pictures of people not animals.The principles of good portrait photography also applies to good animal photography. In the case of this Bald Eagle I used a long lens 200mm and set the lens at a large lens opening f-2.8. The long lens helps you get close to the bird without disturbing him to the point of flight. With humans a long lens works in the same way by giving you and the person some comfortable space between you. The large opening of f-2.8 produces shallow depth of field to separate the eagle from the background which is the same thing you would do when photographing a person.