This year we built a birdhouse out of a flowerpot and placed it on a fence in our courtyard. It was ultimately occupied by a wren. The wren built its nest and raised its brood before abandoning it several weeks later.
Out of curiosity as to how a wren builds its nest, I opened up the pot and carefully removed the nest. I observed something milky and translucent in the bottom of the cup of nest and thought it might be albumen. After carefully dissecting the nest, I realized that the translucent material was plastic. Some of it was from food wrap and was crisp similar to cellophane. Other pieces were softer and in the polyethylene category similar to the plastic used by dry cleaners or on produce bags in grocery stores. One piece still had printing on it. Most of the pieces were roundish and about the size of a quarter or half dollar. There was one strand of rigid plastic similar to that used in electric ties that had been woven into the structure of the nest in much the same manner as the long pine needles and sticks had been used. However, the sheet plastic was positioned in overlapping layers at the very bottom of the cup of the nest where the eggs would have been. Under this was very fine material…possibly squirrel or cat fur, down, or finely shredded wood.
The placement of the plastic sheets appeared to be deliberate to accomplish some specific purpose. I drew this conclusion because it was carefully structured at the bottom of the nest and no place else. It did not appear any place except at the bottom of the next cup. It was not interwoven into any other place in the nest structure nor did it appear higher in the cup. Also, the size and shape of the plastic suggested that it had been cut by the bird as opposed to having just been found.
Do you have any ideas as to what was on the wren’s mind when she built her nest that way? Was she applying a common technique that she might have used with some natural material or was she adapting a strange new building material in some novel way?