Compute what your max aperture would be with the TC on (I think about f/9), then set the lens to that aperture and set the camera to preview/stop down, Then see if the camera will AF at that aperture. If not, see if you can manually focus the lens. If the wildlife will be in shade, you NEED to test the AF in shade as well as full sun. If you cannot AF nor manually focus, problem solved, you cannot use that combination. If you are reaching out that far, you may consider switching from a LONG zoom to a small astronomical telescope that can be used on a tripod, like a Celestron.