In no case is access on the beach above the high water line legal unless you have some specific easement or permission. But if you enter elsewhere, you can be anywhere below the high water mark, as long as you are fishing, fowling, or boating. Case law says birdwatching counts as fowling.
On a practical basis, most beachfront homeowners aren't going to get riled up over someone walking on the sand above high tide to get on through to some other place.
I pick my battles on easement carefully, no matter which side I'm on. It's not a case of being a wimp, but more like showing a little tolerance and respect. About an hour ago I looked out my window and saw two women and about 5 kids playing on the rocks in front of my house, chasing little hermit crabs, inspecting the periwinkles, etc. They were having a good time while not bothering us. Technically I could kick the out, but for what purpose?
Similarly, I generally ignore people transiting down the beach, and if it is high tide generally ignore it even when they climb up the rocks and walk across my grass.
Where I do draw the line is people setting up to fish from my seawall, or to sunbath on the grass in my yard. Yes. People really will do that, generally after walking underneath my house (it's on 10' high pilings) to get to the waterfront. Luckily, that sort of stuff is typically just a couple of times each summer. It wouldn't take too many yahoos like that to get me sensitized and reacting more quickly to people wandering through or playing on the beach and rocks in front of my house.
Charlie Allen