Barn Swallow (Hirundo rustica) nest with Barn Owl (Tyto alba) feathers
Barn Swallows build their nest out of mud and fibers readily in protected areas of man-made structures, like the rafters of barns, or underneath awnings. Inside the nest is a softer medium such as grass or feathers if they're available to cushion the eggs and growing chicks. Here is a magnificent example, coming from a very active Barn Owl breeding building. You can clearly see how the two species are coexisting.