Like I said before I shoot about 99.9 % handheld and do not use back focus. I got my hands slapped a little by a friend who has a Canon 500mm f/4 with an teleconverter. He uses back focus and uses either a mono pod or tripod most of the time. I have also watched a two day seminar online from a world noun wildlife photographer who uses Nikon's bigger lenses with teleconverters and shoots with tripods and uses back focus. But I did notice when using the Nikon 80-400 he went hand held.
Anyways maybe I shoot back wards compared to the pros but like I told my friend the method I use works for me. Also to note the more expensive bigger Nikon and Canon lens 500mm and up are quite a bit bigger and would require a mono pod or tripod. They also retail between 10,000 -12,000 $ But I have been told my wildlife photos are just as good or better then the guys I know personally that have and use 500mm f/4 lens lenses but, I think my photos are sharper.
I shoot single point with AF-C, I like single point because when I frame up the wildlife I can pick my focus point fast with my thumb while viewing the animal through my view finder.
This is the first example from the very first time I had used the Tamron 150-600mm and literally maybe 2 hours or less after purchasing the lens. I was so excited after purchasing the lens that I drove straight out of the city and hit the grid roads looking for something to test it on. This hawk was my first subject. The quality has been down graded from a 46.7 Tiff file to a 3.18 MB jpeg to accommodate posting online.
Alos shot handheld, when I saw the hawk I pulled over past him and grabbed my camera from the passenger seat and approached him from the shoulder of the road slowly with camera ready.
Exif f/9 1/5000/ ISO 2000 @ 600mm
2nd photo shot example from a very cloudy gloomy day with poor lighting and handheld.
Exif: f/9 1/4000 ISO 2500 @ 600mm
The 3rd shot was handheld again and a challenge because it was evening and the sun was hitting the coyote from behind and so the coyote was between the sun and me.
Exif: f/10 1/3200sec ISO 3200 @ 600mm
4th Shot was handheld using the Nikon D7100. All other shots were with the D800E.
Exif f/9 ONLY 1/320sec and ISO 640
OSPREY shot was handheld and the subject moving fast past me along the river.
Exif: f/10 1/4000 ISO 2500 @ 600mm
First Duck I think I used a a tripod.
Exif f/9 1/2500sec ISO 2000 @ 600mm
Second Duck photo the same Exif as the first duck but at focal point 400mm
The picture quality in my opinion is slightly not as good as my Nikon 80-400 and the only fault I find in my opinion with the lens is that it doesn't focus as fast the Nikon 80-400 but then again the Nikon retails at 2800 and doesn't have the focal length and the Tamron I paid 1299.
Will give examples of shooting with lower shutter speeds verses higher later
Last pic is for fun. My setup when using a tripod but after the first use I don't think I used it again. I just find tripods and mono pods to restricting with me and for these lighter lenses I prefer going handheld being able to shoot on the fly and have fun while doing it.