I love water colors and started with them very early on. Problem now is I have two kids running around and cannot focus long enough to 'plan'.
Love your hummingbird! Now you mentioned painting the background in. Rule #1 with water colors, WORK IN REVERSE!! LOL! What I do to preserve my whites and to get a nice flowy background that doesn't seemed 'painted around' my central focus (in your case the hummingbird) is I use masking fluid which is a liquid latex that I paint on dry watercolor paper on my whites and anything I wish to paint in after the background is in. So I lightly pencil my image on, paint the masking fluid on what I want to preserve, wash in my background, allow it to dry thoroughly then peel off the masking fluid and I have perfectly preserved whites etc.
Note - use an old brush as the masking will ruin it unless you dip it in a little water and make it damp before using the masking, then you should be able to just peel the masking of your brush