Parental Protectiveness

Last spring, Mom and I were driving in the refuge and came upon two American Avocets with their baby. They were on the far left side of the road, which is wide enough to easily have two cars pass.

But when I slowly started to drive by them, the parents were not about to let that happen!
First, one came on my left side with his wings open - and he was right at the side of the truck!  I felt that if I continued on he would run into the truck.

So we cruised quietly along with them and the three of them walked down the road - no hurry at all.  The little one scampered along the side of the road, sometimes venturing into the first track, and then back to the side.
When it appeared that all three were far enough on the left side, I went to pull forward, again, quietly.  This time the parent came in front of the truck and I do believe it would have remained there if I had driven on! (this is through the front window and that is the hood of my truck).

So, we had fun just watching these guys, idling slowly along at an Avocet's pace, which isn't very fast when it is very young.  Short legs!  After a while they seemed to ignore us so I slowly idled past them and they ignored me.

What the difference was between them stopping me and ignoring me, I could not figure out.  Fascinating, aren't they, these wild beings that we share the earth with!