Contrary to popular urban myth, the more manual control over the camera, the better our results are likely to be. Most birds are small objects, some are quite tiny. We either get real close, get a telephoto lens or both. Cameras don't come equipped from the factory with a lens suitable for wildlife, so we must purchase one. Fixed focal length lenses with good optics historically produce sharper photographs.
Zoom lenses are versatile and optical quality is improving.
Mirror lenses are built something like a telescope, and comparatively inexpensive. We can't get a small bird to occupy a major portion of the frame with any less magnification. There are many good choices in that range. A word about f-stop and your lens. F-stop refers to the amount of light coming through the lens.