I thought a similar thing when I started thinking seriously about HD shotgun loads. The birdshot tends to blow-up things like melons and such in dramatic fashion, but after doing some penetration tests on many different targets, I quickly came to realize the birdshot just doesn't penetrate well. It does massive superficial damage, but each tiny pellet just does not have the mass to carry itself through. Buckshot and slugs do. Personally, I keep my 12ga. loaded first with two 27 pellet #4 buckshot rounds because I use the shotgun regularly to dispatch critters around the farm, and the balance is loaded with 00 buck for HD. I imagine at close range birdshot would probably give most intruders and attitude adjustment in a hurry, but why use something that is marginal at best when there are much better options available? I wouldn't even load #8 shotshells to dispatch a racoon or a coyote if I had something heavier available (such as the #4 buck), so I surely wouldn't choose it to defend my home from a 200lb. person. Besides, birdshot severely limits your effective range when you're talking about penetrating a heavy target.
Cool video though, and that looks like some beautiful country you've got there.