I have watched Tree Swallows for a long time and this is the first time that I have seen them collecting the feathers of other birds. Certainly, in some places the Tree Swallow’s nests are lined with feathers, but this depends on local availability. In some places grass is used to soften the rougher surface of the nest. So while feathers are sometimes used, there is a question as to why feathers are being brought in on the day the chicks fledged. This would seem to make them irrelevant.
The feathers were always from other species, were all about the same size, and either white or grey. A number were seen on this final day before fledging, but only one of each colour is shown.
Apparently, such feathers have also been used in what appears to be a Tree Swallow game of catch, but this was not seen.
This feather being brought to the nest cavity was white.
This grey feather seemed stuck to the bird’s bill. It went to the nest, and away again.