Today's Mystery Bird for you to identify

Mystery Bird photographed at Heritage Community Park, Blacksburg, Virginia, USA. [I will identify this bird for you in 48 hours]

Image: Audrey DeRose-Wilson, 2 October 2010 (look at this bird with binoculars).
Nikon D80, 70-300mm, f/5.6, 1/400, iso: 160

This neotropical migrant's blue plumage is not based on pigments at all. Instead, it uses another strategy to create blue feathers. Can you tell me about that?

Daily Mystery Bird Rules:

1. Please name at least one field mark that supports your identification, keeping in mind that more than one field mark is often necessary to distinguish between species. IDs without any supporting information are not valid and may be deleted by the moderators.
2. Expert and intermediate level birders: do NOT try to be the first to blurt out the mystery bird's ID. Instead, please provide helpful hints, such as descriptions, literary references, puns, personal anecdotes, and other forms of discussion and assistance for beginning birders and for those following on their iPhones without naming the species. Expert and intermediate birders are free to name the bird species 24 or more hours after it was first published.
3. Each mystery bird is usually accompanied by a question or two. These questions can be useful for identifying the pictured species, but may instead be used to illustrate an interesting aspect of avian biology, behaviour or evolution, or may be intended to generate conversation on other topics, such as conservation.
4. Each bird species will be demystified 48 hours after publication.

If you have bird images, video or mp3 files that you'd like to share with a large and appreciate audience, feel free to email them to me for consideration.