The evidence: Shreds of cocoa fiber from the hanging strawberry basket found on the deck.
The culprit: A female goldfinch (Carduelis tristis) plucking fibers for her nest. What a cute mugshot! She was so intent on gathering materials that she didn't mind me shooting this photo.
This (mid-July) is prime nesting time for goldfinches. For a couple of weeks, the males have been zooming after each other. Their bright color and lively squeaky voices make them one of my favorite backyard visitors. Hear them at: http://www.allaboutbirds.org/guide/American_Goldfinch/sounds