Skull is great! For true depth, I would recommend very soft charcoal pencils for the bird. The shadows become so deep with soft charcoal. Even matte graphite at 10b, 12b or 14b would sink your darks even darker.
not sure if it's the photo but adding a highlight tone would make this look more dimensional and less flat. Right now it is giving old sepia photo with low contrast. good composition, rendering skills and mark making though. going through with a kneaded eraser made to have a point, and then hitting the parts of the piece that would have a highlight would make your darks look darker and add a layer to the molding of the shapes. if the paper is toned, adding a tone lighter than the paper drawing in the highlights on the points of surfaces, would also work.
Looks really good.
Maybe you could darken a bit of the shadows under the raven wings to increase the contrast with the skulls, but it's already a really good image.
The skull looks great but the lack of dark range on the bird flattens the whole picture for me. Carrion crows are pure black so while yes there are highlights It's a little odd that the biggest dark area is under the skulls chin and not the pure black bird.
Skull is great! For true depth, I would recommend very soft charcoal pencils for the bird. The shadows become so deep with soft charcoal. Even matte graphite at 10b, 12b or 14b would sink your darks even darker.