Brown Creepers build their nests behind pieces of peeling bark. I found this nest building activity in a local park in the spring of 2021. Getting a good portrait of a Brown Creeper is challenging since they live in dense forests. I finally nailed one good portrait:  I was very lucky that the nest being built was in a very visible location and not too high in the tree. I spent two days watching them bring in material. Both males and females are involved in the construction, but one of them did not have a good sense of scale, bringing in pieces too large to fit into the opening.  The next try was far better: I returned a few weeks later hoping to get a glimpse of the Creepers again and to see a chick, but unfortunately the nest was not successful. It either fell out the bottom of the pealed bark, or it was attacked by a raccoon. At least it was fun watching them build the nest.