Define "densely populated wild bird area".
What you see on YouTube is mostly preserve "hunting" (using the term loosely), & they're shooting mostly flare nares (pen reared pseudo roosters). It's important to remember that whereas SD does have far more wild pheasants than any other state, they're not just spread out all over the place. At any given time, a localized population of pheasants (for the most part) uses relatively small, specific pieces of habitat, & they use them for specific reasons. If you don't hunt the right spot at the right time, you'll see very few birds (with some exceptions, where you might just get lucky). That's the hardest part, but it gets easier with experience. What makes it harder in SD is that there are so many options (some just a tad bit better than others; therefore holding more birds), whereas in other states, there's just way less habitat, making any birds in an area much easier to find.
If you end up on public land with no dog, then VERY small groups, like 1 or 2; 3 at most. So be prepared to split up your larger group. It can be done though. Absolute silence before hunting (getting out & loading up & stuff) & while hunting. Use hand signals. Hunt into the wind as much as possible. Hunt small pieces of cover where escape routes are minimized &/or you can pinch birds (which can include 2 hunters hunting right toward one another). Try to hunt a spot in a direction somehow different than the last 20 people/groups that hunted it. Try to anticipate escape routes, & silently position a blocker there. Hunt slowly, in an irregular pattern (like zig-zaggy), & stop often (like for up to a minute or 2). If a pheasant is nearby & you stop (still maintaining silence), this is when he's likely to get nervous & flush, or when you take the 1st step again. Hunt the lightest cover possible that pheasants might be likely to use, given a particular time of day & weather conditions. You have to be the dog, so you have to kick through as many square inches as cover as possible, while still covering ground. It's a learned balance. All in all, it's much like hunting SD public land with a dog, but you have to be even more vigilant about the details if you want to see/shoot a few pheasants. Hunting ditches would be another good option, hunted in a similar fashion. Leap frog. One guy gets out to hunt, while the other drives up the road a distance & blocks (yes, pheasant will sometimes escape simply by running down a ditch). Alternate walking & driving/blocking.