I'm also with you on this point-the keeper rate of shooting my 400L from a tripod, vs. handheld is definitely higher. I was VERY interested in the 100-400 Sig when it was first announced, especially when I learned it was compatible with the 1.4TC (for the 150-600)that I already owned-the lack of tripod support has dampened my enthusiasm for the lens considerably. Guess at this point, I'll wait until the GSM Photo Summit in November, where I can borrow one from the Sigma rep to try, before making the decision to buy. Who knows, Sigma may realize they've stepped on their d*%k with the their golf cleats, and develop a solution by then.

Jim, I am hardly an exceptional photographer, but thanks for the thought.

What I am is a pretty average photographer of 50 yrs, with decent skills, and a never ending thirst for knowledge and how to improve what I do. Seriously. Not being falsely modest. I do meet truly exceptional photographers all the time, and love the opportunity to learn at least one thing (hopefully more), from each of them. And as generous with their knowledge at they can be, I try to do the same here and in other areas. I teach and mentor beginners and working pros alike, and doing that helps me pay for new equipment without involving our household budget and "permission" from the wife.

What I do with a long lens is far from magic or exceptionally skillful. I just stand like a person on a rifle range, with my body aligned to the direction I am shooting (not facing front, but with my left shoulder pointed at my target), my left elbow is dug into my ribs, my left had supporting the lens from below, right finger pressing the shutter, and like Imagemeister says - using head and face to further stabilize the camera. If the subject is a perched bird, I breathe normally and wait until I exhale, pressing the shutter at the end of the exhale. If I am panning for a moving subject, I rotate at my hip to follow, not upsetting the equilibrium of my upper body. The quieter your upper body is, the better your "keeper rate" will be. A quiet upper body is something I taught intermediate and expert skiers to get them to stop crashing and make cleaner turns. It also works well for photography.

I recognize I am using the wrong camera for this - a D800 is hardly a "go to camera" for shooting active subjects. But I do get what I set out to get, most of the time, anyway. I'd say my keeper rate ranges between 10% and 30% or higher, depending on what I am shooting and where I am. With perched birds I can hit as high as 70% in good light, or as little as 10% in poor light, where the camera has trouble acquiring focus. The first image, the cowbird, was one of those - ISO 1000, but the best I could do was 1/30 sec. I totally relied on the bird not moving and the OS on the lens doing it's thing. I fired off 8 shots - I got 4 without movement from my camera, but in the other 4 the bird moved. Of the 4, the best composition was the one I posted, I have already deleted the others - so for this particular bird my "keeper rate" was 1 in 8, though 3 where technically ok, just not aesthetically to my liking. It varies like this all the time. Recently I was out west, and spent some time at Yolo Bypass nature reserve, and shot 75 pics of burrowing owls. All of them were in focus. But I only really liked about 6. Technically, my keeper rate was 100% - but from an aesthetic point of view, less than 10% were shots I was totally happy with.

I shoot the Nikon D500 with the Nikon 200-500 f5.6 lens hand held for birds in flight. I generally shoot in Group Auto Focus using the center spot on my camera, Nikon then puts 4 spots around that one for a total of 5. I shoot at 1/1600 sec. minimum but usually higher around 1/2500 sec at f6.3. I have NEVER used a tripod cause it gets in the way and I can track a bird easier hand held without a tripod. My keep rate is almost 98%. The only time I use a tripod collar is to reverse it so I can use it as a handle to carry around. I shoot over 10,000 images a month without a problem. Tripods just do not make it for birds in flight.