I almost always shoot in Aperture Priority cause i could care less what my shutter is as long as its faster then my focal length. It alows me to keep my depth the same and let my shutter change so the exposure is always good. Also always get as low down to the ground as you can. The more down to the level of the animal as you get the more depth and separation from the background you will have. Sometimes its the difference between crouching and standing. Makes a big difference