Certhia americana

As the days pass and spring progresses, more and more migratory birds are appearing in Yosemite Valley; and they, along with the year-round residents, are making the necessary preparations for breeding.

The Brown Creeper, a small, tree-climbing creature, spends its whole year here; it's tinkling twitter can be heard at times of the year when very little else is stirring. This morning I came upon a pair cooperatively building a nest behind a mossy flake of bark still clinging to a dead tree. Creepers are known to almost exclusively select nest cavities of this sort, using twigs and strips of bark to line the nest.

In this picture I caught the female bringing in a bit of bark (she's on the right side of the tree). This is the first creeper nesting behavior I've witnessed and it was just great. It was a real treat to watch, and to capture with the camera.