I spent a few hours on Saturday in the desert of Arizona and witnessed something interesting. I observed an encounter between a wren couple and a lizard. The birds were agitated, flying around a rock some 50 meters up the slope. I began approaching them cautiously. The birds did not pay attention to me and I came fairly close. They were flying around a gap in the rock and peeking inside with the feathers bristled. Suddenly a lizard stuck his big head out of the rock. It became apparent that the lizard had entered the nest of the birds. The birds were trying to drive the intruder away. The lizard poked his head annoyed several times more while the wrens were circling around at a distance. Eventually the poor birds flew away.
I felt for them.