SCRAPERBOARD, or SCRATCHBOARD is a particularly interesting medium for anything with fur, feathers or wings.
It involves a process of literally ‘scraping’ a layer of Indian ink off white card – something like ‘ etching’.
Extremely fine work  but ideal for such subjects. The Butterflies are in fact three separate pictures, joined. 
I also  draw and paint animals in pastels or colour pencils.

CLICK ON AN IMAGE, BELOW, RGE