Grass is one of the most expensive things to draw on a big island, so it is handled in 16 metre cells. The world remembers where every clump goes, and only what the camera can actually see gets drawn.
Close grass uses a detailed model, and further grass swaps to cheaper ones. The swap is a 14 metre crossfade, so you do not see it happen. New grass fades in over about two seconds with a small random delay per clump, which avoids square patches popping in. The outermost band blends into the colour of the ground and the distant meadows.
The camera can zoom out far enough to scan a field for animals. Zooming does not change what the animals can sense. They still react to you through sight lines, sound, scent and how well you are hidden in the grass, so a wide view is not protection if you are already close.
Moving the camera alone makes no noise and does not move the player.