Baltimore Orioles have nested in this linden tree for at least two previous breeding seasons. Do they ever recycle their old nests? Or the materials contained in them? There’s a lot of human-made material incorporated in their woven bag nests, including ribbon (many bunches of flowers in a cemetery…) and string. This stuff doesn’t break down as easily as the more traditional nesting material of grasses and plant fibers.
Backyard and Beyond 
That the ribbons and string degrade more slowly than grasses and vines has to be part of why the orioles use them. I think there is also an aesthetic reason. The nest decoration, while not complex like a bower bird, still shows an element of style and an awareness of color. We are not the only beings on the planet with a sense of aesthetics.