Using a flat brush dampen the background area with clean water.
Do one area at a time, so the forward painting edge stays damp to prevent a hard edge.
It seems to work the best to not pre-wet right up to the edge of the bird or flower.
Paint right next to the bird and flower when you are painting on the background color.
If you pre-wet right up next to them, it makes the color pool up against their dry edge.
Make some marks behind the bird to simulate flight movement.