Here is an American Tree Sparrow:
While the Tree Sparrow is quite visible in this shot, it is easy to see how well it is also camouflaged in this environment. American Tree Sparrows can be seen later in the spring when there is little snow on the ground, but perhaps this camouflage indicates that it needs protection most during the harsh winter when the branches are bare.
In person, it looks even more blended in with its environment. Due to the nature of long lenses having a thin depth of field, the bird is more isolated here, and of course we can also see its face and eye, whereas when it is moving around rapidly or its face is not visible, it is even harder to see.