I too noticed the black outline on the top/back of the bird but not the front/bottom. A pencil line probably wouldn't stick as well to the underside if the embed was already hard and dry, whereas a sprinkle on the top wouldn't have gravity working against it. A thin black pour seems more problematic to me but that does not mean its not possible.
I think you're probably right about adding the beak -- and I'd say the eye too. I wondered if they were added after the bars were cut (i.e., just superficial), but when you blow up the pics they don't really look like they were painted on there.
Well, they are just the cutest things and they'll have me pondering -- and aspiring -- for a good long while!
maybe black mica and oil painted on edge of bird and left to dry