It's barely larger than my thumb! I didn't realize that we had these coming though the Chicago area. They don't nest here, but pass through in Spring and Fall. They're cute, tiny, tough little birds that have extraordinary vocalizations. Several years ago, I was fortunate enought to be back country camping in the Olympic Rain Forest in the Pacific Northwest. My husband and I moved along the thickly ferned trails, and at one point could have sworn we were being followed by a mouse. We stayed still for a bit, and the culprit revealed itself to be a Winter Wren flitting about in some brush. Their song is a complex series of very high tinkling trills (like the tiniest wind chimes you can imagine), and thin buzzing.