Wrens are notorious of many things... stealing nestboxes from bluebirds and tree swallows, destroying eggs or the hatched young of the birds in the nest, and dummy nests. About a month ago as I lifted the lid to one of my three nestboxes, I was happy to see a few small twigs in the bottom of the box. I quickly decided that a wren was planning to move in, and my suspicion was quickly confirmed by a wren call from a hedgerow a short distance away. I immeadiately wen inside and plucked my field guide off of the bookshelf. Flipping to the house wren page, I read the species notes and learned that male house wrens often place a few small twigs in the bottom of all prospective nesting cavities, and then the female chooses the box she wishes to use and then finishes the nest building process. I placed my book back on the shelf and then went to investigate my other nestboxes. Box two: nothing. Box three: a few small twigs in the bottom.
The next day I went back out to check both of the boxes. Sure enough, the nest in the first box near the hedgerow had been built a little bit bigger. This trend continued over the next few days. I was looking forward to the nest full of little wrens that would surely be in the box in a few more days. Normally I would have ousted the wrens upon discovering their nest, but since the bluebirds and tree swallows were done nesting for the year, I decided to let them go. However, soon after the nest was completed I realized that the wrens had no intention of raising a brood in that box. They had built a dummy nest.
So what exactly is a dummy nest? A dummy nest, mainly built by wrens, but also by a few other select species, is most easily described as a "fake" nest. The nest is built just to keep other birds from using the box. When another bird sees the nest in the box, they believe that the box is in use when it really is not. Sometimes instead of building a nest, wrens will jsut fill the box with a jumble of basically anything that they can find. On the extreme side, wrens sometimes just stuff a nestbox entrance hole with nesting materials so that other birds cannot even enter the box.
This is just one example of an interesting behavior that characterizes one type of bird. If you look closely, msot birds have a certrain trait that distinguishes them from all other species. Wrens build dummy nests, flick their tails, sing nearly al day long, etc, etc.