How do they know how to do that?
I use to photograph a local Deer herd or herds (I could never determine if it was a huge herd or several on the same property) with a Canon 300mm 4L and occasionally, with telecoverter, giving about 600mm.
This was a large preserve by a Duke Power coal fired electrical power plant, mainly for Geese, Ducks and other migrating and residential waterfowl.
What I found was, without a blind, it was a matter of setting up, tripod, ect., while the herd was making the rounds on the property and simply settling in, not trying to put the sneak on them or appear to be hiding, but calmly, quietly waiting there, motor drive off, and at first focusing my attention elsewhere, the nearby pond usually had birds enjoying its being there.
Keep in mind, these were corn fed waterfowl and deer, so they did not spook easily and go off and hide during the day.
After awhile, the main part of the herd would often wander much closer to me and even in the rut, mostly ignoring me, my camera and usually a friend that would accompany me on these shoots.
There's no stopping quick, jerky motions in a herd, but there was over the day, ample opportunities to get decent shots, including some close in head shots with that basic setup and no place to be that was not where I was.
Man fed herds usually tolerate the presence of a few people, especially when they grow use to seeing you and your kit, but not everyone has the patience or, no longer possess the ability to limit their movements, but if you want the shots, you can get them, with this technique or others used by real wildlife photograph professionals.
In my, old, limited experience.