It is Illegal, and it's B.S.
YEP!

I waited untill late april last year to go to one of my favorite reserves (after the animals were on there way out) only to find four wheeler tracks every where and no sheds

It depends on where your going, there are some areas you can't enter untill may and some declared reserves. I did some research last year and found a couple of reserves you can enter as long as you don't harass the wintering animals, but thats a grey area, so i try to wait untill the snow is gone and the herd is disspursed. Looks like I waited to long last year

Just make sure and understand the laws in the area where you want to go.