Can anyone tell me what this is on the tail of this Barn swallow?

http://www.flickr.com/photos/25348030 at N07/2476112252/

I took this photo in May of this year. I noticed a posting a few days ago where someone else had seen a strange Barn Swallow tail and it made me think of this photo.

Take care,
Dea
Steilacoom,WA