I can offer no argument against knowing a subject's anatomy, this is especially true with hairless or shorthaired life forms, where sub-derma structure of bone and mass are visible at the surface.
That said, birds offer the artist, relatively smooth uninterrupted visual forms. The feathers provide an envelope covering musculature and simplify the surface into balls and triangles for an initial sketch. This is where the challenge begins. Proportion and detail, the former being the more important quality from my perspective, must be addressed. How accurate do you want to be?
Study your chosen subject and place the anatomical features, like eyes, beak, and, feather placement in their correct location and proportion and you should produce a satisfying image.
I personally have two architectural scales and one engineering to help accurately position features onto the surface. You could also consider projecting the image. Measure, sketch or, project, you choose but, from experience, I've found accurate anatomical placement will go far toward giving you a realistic drawing and is more important than detail.
I try to think like an impressionist when I'm burdened by the desire to add detail.