Many times when I am out looking for bird photo subjects, I am usually using a 400mm lens with a 1.4x teleconverter. Sometimes I will also carry an Olympus m43 Camera with a 14-140mm lens for landscapes or views that I like that need a wider view, giving me a FOV equivalent to a full frame SLR of 28mm to 280mm. But if I am walking around a big area, I just carry the Canon body with the 400mm & 1.4x teleconverter. So when I come across a cooperative close bird or other interesting subject, I then shoot a series of images as quickly as I can, handheld. Using a tripod slows down the quick shooting process and I let Photoshop align them. Usually I try for at least 4 or 5, but have had some success with 2 or 3. Depends how cooperative my subject is. This immature Little Blue Heron was an example of one overly cooperative subject. I was at Ding Darling NWR and I was photographing birds that were out on a sand dune and this one kept coming up to me. There had been a few fishermen there before me and were feeding him fish. So I guess he thought I would do the same. After a while he just caught a lizard and wandered off. Then he kept wandering around the area behind me on the other side of the Wildlife Drive. He was looking for a meal so I shot a few quick series of different images for some panorama series. Some vertical, some horizontal. The trick to this is a series of images as quick as possible because the subjects usually are moving. Handheld images are then aligned in Photoshop and then retouched to add either a missing area of background or just fine tuning here and there. The featured image is a 2 image pano of the walking Egret. Below is a series of panorama images shot at 560mm, then assembled in Photoshop. Then blank areas outside the assembled image were filled in by Photoshop. Once you get used to using this technique, they seem to come out more consistently. This also gives you large files if you really want to print them large.
Selecting images for the panorama in Adobe Bridge to import and assemble in Photoshop