1. I love the opportunity to sketch warblers; they seems like such rare glimpses when I spot one.
I felt like I had the body proportions ok, but it was challenging for me to illustrate the fluffiness of some of the wings, and also present the bird as not from a full side angle (though I won't know that next time I look at my representation ;-) ).
2. I wouldn't have noticed the details of the beak, or the type of branch (which I didn't even draw clearly, as I focused more on the bird itself); or the variety and differences of feathers. It really helped me look for details and notice them.