Know more than you Show
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.
Lightly block in the proportions of the bird. How big is the head relative to the body? What is the wing length? Tail length? Primary extension?
Once you check and approve your proportions, you can start blocking in feather groups, head-to-toe. It is a good ideas to start with the face. If the bird’s expression does not look right, no amount of wing detail can fix that. Face first. Once it is clear, move on to other areas.
Continue blocking in major feather groups. Avoid outlining every feather in the wing.
Add detail in focus areas (here the face).
Paint shadows with a dull purple-gray mixture.
Paint gray areas with watercolor, then let it dry.
Paint the yellow-green regions. Oh no- I did it again. Here is an example of one of my most common mistakes. I work and balance areas of color only to realize that the whole thing is too pale. This wan not done intentionally. I would love to get this done on the first coat but I will need to deepen the colors. I call this anemic watercolor.
Here I have added more layers of color to build up the values.The wing is dark with pale edges on the primary and secondary feathers. Here I paint the whole wing the edge color as an undercoat. See what happens to the wing in the next step.
Now I add the dark on the wing tip and draw thin lines of brown up the wing leaving the pale edges. Note that the pale edges do not extend to the wing tip.
I want more texture and slightly darker values so I add texture with a fine tip brush. I know it looks too strong but much of that dark will be covered with gouache.
Now I use a layer of semi-transparent gouache on the back and breast to unify the the colors and beat back the texture marks on the breast.
As a last step I strengthen some of the lines around the face and body edges. I avoid the temptation to outline the edges of the wing feathers.