A robin has been hard at work on a nest just outside--and below, which makes it ever so convenient to observe--my study window for the past two mornings. Three times, so far, a red-breasted nuthatch has come along to investigate. The nuthatch flits from one yew branch to another, ever closer to the nest. The robin watches her with increasing vigilance as the distance between them decreases, then makes a run at her if she comes too close. I would suspect "nest mining," but for the fact that the nuthatch doesn't come in for materials when the robin is out gathering new mud. The robin seems to be carrying mud, but it looks like worms. If I couldn't see right into the nest, I might conclude that she is feeding hatchlings, especially since the motion she uses to place the material looks so much like jamming worms down the maws of young. It appears that the "worms" are pieces of stringy vegetation coated with mud (the mud lining is slowly building up as I watch). That seems like an efficient way to carry more mud than she can fit in her mouth. So many questions. Is she using roots that are already muddy? Does she prepare fibers by taking them someplace muddy so she can get them all nice and gloppy? If only I didn't have to go to work!