Once upon a time, we had a peaceful backyard. (Cue the Disney fairy meadow music.)
The Eastern Bluebirds had a successful brood in our Bluebird Nest Box and started on a second family; but, Evil European House Sparrows attacked the second nest, destroyed the eggs and chased out the Bluebirds (cue sound track from Psycho).
In the US, Evil European House Sparrows are not native, are very destructive, and considered a pest. They are one bird species not protected by the Migratory Bird Treaty Act, so we Nest Watchers are allowed to interfere with their nest building and allowed to trap them, but responsibly. Once the Evil House Sparrows were gone, the box was available. (Cue Disney music again.)
A little House Wren (illegal to harm them, but still a threat to Bluebirds) started to build a nest (out of twigs) in the fresh Bluebird's box.
But then the Bluebirds came back (cue music from Jaws), and started to build a nest of grasses on top of the Wren's twigs.
Then the Wren came back and threw out the Bluebird's grasses.
The Bluebird came back and said, "Hey, where's my stuff and what the h#ll are YOU doing in my house?" and chased the Wren away.
The battle for occupancy continues to wage. All I can do is watch and hope the Evil House Sparrows don't ruin the plot.
Who knew that bird watching could be this exciting?