Both of the shots above were captured with a Canon 1D Mk IV and a Canon EF 800mm f/5.6L. The image of the mountain goats used a shutter speed of 1/500 and the bear was even slower at 1/320. I could have easily increased the shutter speeds by increasing my ISO but I was trying for the cleanest image I could possibly get.
Such shutter speeds are definitely possible but when on a moving boat and compared with an effective focal length of 1040mm, the results are impressive. I used the image stabilizer in Mode 1 which helped significantly but the real reason I could shoot with certainty at lower shutter speeds is my support setup.
I used a Really Right Stuff camera support setup including TVC-33 tripod, PG-02 gimbal head, and a long lens support package as depicted in the images below.
If you are a long lens shooter give yourself the advantage of perfect support. I often say there is not a gear/technology solution to every problem but in this case I could not have made the same shot without it. When combined with a good foundation in exposure and camera/lens functionality, the support system makes a nice trifecta!