Several folks have written to ask about the strip of black material in the nest. It is hard to tell exactly what the material is from--it is several feet long and flexible. The female does rearrange it on a pretty regular basis. She can't seem to decide how exactly to incorporate it into the nest. hawks and other birds will incorporate all kinds of materials, both natural and man-made, into their nests. If you see the red-tail's nest up close it is actually loaded with all kinds of garbage. I have watched songbirds pull the soft filter material out of cigarette buts for their nests. A lot of the time the man-made materials just become part of the nest structure.....but some materials are problematic. One material that birds are particularly prone to picking up is strings, lines and flagging material. Nestlings can easily get tangled up in this material. The picture below is of a barn own nestling dangling from a nest on a bridge over the Tualatin River that we had to rescue last year. Another good reason to pick-up our garbage!