It is sometimes acceptable for a part of a bird or animal or other living creature to be out of focus or blurred. Movement (such as a birds wings) and depth-of-field are both potential reasons why it *might* be acceptable in a certain image for a part of our subject to be out of focus.
Generally though….what separates a potentially good photo from an automatic reject is the eyes. The eyes MUST be in focus. Generally the sharper the better.
Consider these two macro images. Both have sections that are blurred due to the depth of field. Both are generally pleasing, but the dragonfly loses points due to the eyes being out of focus. Depth of field is always an issue in macro photography. Often the depth of field for the focal length is shorter than the item being photographed. A future blog post is in the works on potential ways to deal with this issue.
Birds are especially important. This cardinal photo was taken from my kitchen looking out into the backyard. I was worried about its sharpness because it was captured through the glass window. I think that most of my attraction to this photo stems from the contrast between the sharpness of the feathers, eyes and steel cable and the bokeh of the background.
Of course, we’ve all taken the photo where our subject blinks, or has their eyes closed. Even birds, mammals, etc. Some birds, reptiles and even mammals have a “third-eyelid” or a Nictitating Membrane. Photos taken with the nictitating membrane partially or fully closed will generally be rejects.
When using auto-focus, make sure your focus selector is set on the eye. It may not be a “keeper” but without the eyes in focus….the rest of the image really won’t matter.