Likely to be Utah's 10th accepted record of the Prothonotary Warbler.

The structure this individual is perched on is a hollow iron post used to (i think) support a volleyball net--there are two such posts, each attached to an automobile tire--in the area. The bird was poking his head in and out of the post. According to http://www.allaboutbirds.org/guide/prothonotary_warbler/lifehistory

"When courting, the male flies close to the female and both birds chip softly. The male shows off possible nest cavities, entering and exiting them. Once a pair forms, the male guards the female while she is building the nest and laying eggs."

The bird also flew off to visit a Yellow Warbler nest located about 20 yards away a few times. I posted a sighting of this nest as well.