When taking pictures of wildlife, a high optical zoom lens is necessary to capture many animals in the wild. You will want to be able to stand far away to keep from startling your subject and to protect yourself from aggressive animals as well as to capture those you can not get near like a bird sitting high in a tree.
Digital zoom is different from optical zoom. Optical actually zooms in on the subject, like a telephoto lens on a SLR camera. Digital basically crops and enlarges a portion of the picture to bring the subject in closer, causing the image to lose quality. This is the same kind of effect you would have if you were to enlarge a picture beyond its normal size on a photo editing program like Paint Shop Pro.
A camera with a high megapixel can also allow you to get close ups of wildlife. The higher the megapixel, the larger your image will be without losing quality. Therefore, you can crop your picture to focus on your subject without having to enlarge it afterwards to get a decent size photo.
This feature allows you to stand just inches away from your subject to get a close up. Without it, you would have to stand about a couple of feet or more away to capture a clear shot. This feature is especially handy when taking pictures of small subjects like bugs.
Below Pictures: butterfly (using optical zoom), owl (using digital zoom), cicada (using macro) - click on images to enlarge