Ed,
I usually draw them in with a pencil prior to carving or burning.
In addition to the feather layout, I draw in splits and shade in
the contours and any other details that I may want. This helps
me visualize more what I want. On my website, as part of a larger
demonstration, I have some photos and a discription of how I put
in feathers. If it would be helpful, here is a link to the page where
I start the feathers(it is about half way through the demonstration).
http://www.jaminmark.com/das/process8.html
On feather layout: All birds have the same feather groups no matter
what the species, varying only in size and shape of the individual
feathers. For instance, all birds have three tertial feathers.
You will have to look at reference for an individual bird to get the
specific feather size and shape, but here are a couple of sketches
I have done of the feather layout of a folded wing and an opened
wing.
Folded wing:
Open wing:
Notice that the middle secondary coverts are stacked in the oposite
direction from the greater secondary coverts.
Hope this helps,
David