According to Wikipedia,
Wildlife photography is a genre of photography concerned with documenting various form of wildlife in their natural habitat. It is one of the more challenging forms of photography. As well as requiring sound technical skills, such as being able to expose correctly, wildlife photographers generally need good fields craft skills. For example, some animals are difficult to approach and thus a knowledge of the animal’s behavior is needed in order to be able to predict its actions. Photographing some species may require stalking skills or the use of a hide/blind for concealment.
While wildlife photographers can be taken using basic equipment, successful photography of some types of wildlife requires specialist equipment, such as macro lenses for insects, long focal length lenses for birds and underwater cameras for marine life. However, a great wildlife photographer can also be the result of being in the right place at the right time.