An interesting behavior we saw multiple times on Isla Isabella is that while boobies would hold their ground as you approached them, their anxiety level would clearly increase as you got closer. When you got to within about 6' of them, they would start "walking in place", alternatively raising their left and right feet. If you persisted, when you got to about 3'-4' of them, they would sometimes pick up some grass, reach out toward you and drop it on the ground as though offering you a bribe if you would just please go away.

Here's an image of one in the process of doing that (sorry the focus isn't as tight as it cold be).