One of the best ways to approach the fauna is with a boat. Mainly in the Pantanal, where most animals are concentrated along the banks of rivers or rivers themselves. On my last trip to the Pantanal we tried, without much success, to approach a family of giant otters. Unfortunately they were extremely skittish due to the fact of being with a cub. It's amazing how fast they swim literally in a matter of a few seconds can travel a hundred meters under water.
However we find an otter allowed a little more approach. We were following her down the river with the silent electric motor. Gradually she was getting used to our presence and returned to hunt. He caught a fish and went room to eat it. Our chance to get closer to take some photos. We managed to get very close and I and my clients did great photos that usually skittish species.
On the boat I shoot with 600mm, well positioned with the tripod, so that I can shoot on both sides of the boat. Of course, who stands at the bow has the advantage of shooting power forward as well. By positioning the tripod on the boat it is important to make sure that it is level and also your legs occupy much space as possible (beyond the normal opening), ensuring better stability and more security.
As the boat normally is in motion, the taste of the current, it is difficult to achieve focus with the traditional mode of AF (single, from Nikon), because when you focus and recompose the subject may have already left the focus distance. The solution is to use continuous focus and change the location of the focal point to can avoid that centralized composition. Thus even with the boat moving the focus is always updated.
The same technique is used to photograph many other inhabitants of the riverbanks:
Tapicuru-de-cara-pelada (Phimosus infuscatus)