What is attacking the sunflower?

Twice now, the sunflower has started a blossom and something has snapped it off in the night. This time the flower had opened and the whatever-it-was tore it apart. I did not plant the sunflower, it sprouted from a seed off the feeder. I've noticed that another flower head is partially cut and hanging. That suggests something small. Several more are ready to bloom, so we'll see if they survive the night.

The bunny came by and nibbled on some plantings between making mad dashes for shelter. I couldn't detect anything to startle it, maybe it was just practicing?

The hummingbird also visited the rosemary again but so quickly that even with the camera ready to go, all I got was rosemary. A dove sat on the feeder lid which is odd since they are ground feeders. Other than that, the usual birds - cardinals, house finches, titmice, and chickadees squabbled over a place at the feeder.

A very tiny brown bird, most likely a wren, hopped around under the azalea. I saw it again in late afternoon under the hibiscus. I can't see an eye stripe and its tail isn't cocked, but both the dark back and the light chest are unmarked so I cannot think what else it could be.