CompositionComposing a shot aesthetically so the components of the image--the foreground, subject and background appear to the viewer in a balanced and pleasing manner is an inherently artistic concept. Unfortunately this means I am not well equipped to say much about it. I highly encourage you to seek composition instruction from some other source. The next page ( Composition links.htm ) might be a good place to start.
I do tend to know a good photograph when I see it. But discussing why it's a good photograph isn't one of my strong points. There are some obvious rules like "don't chop the subject's head off." In other words for all animal shots, human piscatorial avian or otherwise, if the subject's head is included in the shot, the viewer usually wants to see all of it. Usually doesn't mean always however.
If you want to make a photograph that has visual depth, perhaps with majestic mountains in the background, it often helps to have an interesting and sharply focused foreground. To do that you need maximum depth of field. Wide angle lenses have greater depth of field then telephotos. So a wide angle lens set to a small F-stop might be the photographer's best choice (read the depth of field page under the Exposure section). Keep in mind however, that wide angle lenses do tend to reduce the apparent height of background mountains or trees. Another easy rule is the photographer's infamous "Rule of Thirds" law. If you make a photograph of an American Robin with no visible foreground and nothing particularly interesting in the background, that photograph will like seem awkward if the Robin is placed dead center in the final image. That same Robin will likely produce a far more pleasing image if it is placed somewhere near one of the intersections of a tic-tac-toe like grid that divides the vertical and horizontal view-frame axes into thirds.
If you want to make a photograph that enhances or even exaggerates the apparent height of background mountains or trees, then use a long telephoto lens. But you do pay a depth perception price for those taller mountains. Everything in the photograph will seem far away.
Perhaps the most difficult aspects of bird photography involve finding an interesting bird, getting close enough and focusing the camera before the bird flies. In order to snap a shot quickly the bird photographer often has to position the subject dead center in the frame, get the camera focused and snap the shot quickly. In that sense composition has to happen later, during a software post-processing stage when the image can be cropped so the main subject is adjusted away from dead center in the final image.
Rules are never universal. Rules can always be broken. That's what makes it interesting.