This was drawn in permanent ink on paper, using the shading techniques of hatching, cross-hatching and scribbling. I believe this bird is some kind of warbler.
"Canvas Stretcher Pliers and Car Keys"
A different technique is to sketch with water soluble ink and then go over the drawing with a wet, blotted brush to create the shading.
"Baby Otter and Cuppa Joe"
I like this technique better than the last one. First, you sketch an object's outline lightly in pencil. Next, a water soluble ink wash is applied to create the shading. Once dry, you then add specific textures and details in permanent ink. It produces a "crisper" finished product, it seems to me.
Right now, I'm taking yet another class: "Sketching in Pen and Ink and Watercolour." The same basic ideas but with the added difficulty of watercolours thrown in. I'll post some results from this class probably in August or so.
[Photos taken by My Rare One, July 2019]