The colony is close to the water at high water mark and people walking do disturb the birds, don't know if they just get used to people or just get upset !!
This particular day we were there it was low tide and plenty of room to the water, birds were flying from someone walking close to the colony disturbing them. With us photographing one or two will take to the air and make passes but not in mass. There are some volunteers that check on the area regularly and will tell people to back off even if you are not close to the ropes. They educate the public on the dangers of harassing the birds when they are on eggs, do a great job !!
Skimmers and Terns can get quite defensive. I've seen a skimmer that 'attacked' a backpack that someone left on the beach while photographing and it was not even close to the colony.