One of the secrets to a successful bird illustration its to understand bird anatomy, and then suggest detail without noodling in every feather location. To accurately draw feathers, you must understand feather groups and wing structure. I think the best book on the subject is Birding Basics by David Sibley (also available in a spanish edition). Once you have mastered the anatomy and structure, back off and imply feather detail instead of showing everything you know. Many feather edges are soft an do not show obvious edges when observed from a few meters away.
In this step-by-step I try to imply feather detail and structure instead of harshly outlining every feather. Linework is done with a ball- point pen. If you like your linework but are frustrated when you loose much of it with applications of watercolor or gouache, try sketching with a ball point pen. Your lines will remain strong and crisp, even under layers of paint. Color added with watercolor and gouache. Click on the first illustration to start a step-by-step slideshow.