Carolina tractor wrens?

A pair of Carolina wrens have built a nest in the same place in my tractor for the past five years. Each spring they raise a brood of baby wrens. When I need to use the tractor, I check to see if the nest is there. Before I start the tractor I remove the nest and set it aside close by.

Mr. and Mrs. Wren seem to understand what I am doing. If there are eggs in the nest or babies in the nest when I set the nest aside, the parents remain vigilant. When the tractor comes back, I park it in the same exact spot in the shed and put the nest back in its place.

I took this photo the morning of May 2, just after the fledglings flew the coop. I counted four. The parents will continue looking after their young for a few days after they leave the nest, bringing them insects to eat and fussing to keep predators' eyes off their offspring.