In Kathleen's wonderful book-length essay "Living Color: The Interactive Arts of Sylvia Plath" there is a reference to a book, An Ear for Uncle Emil by E. R. Gaggin, Plath read that wasn't - but now is - listed in her library on LibraryThing. Plath presumably read this book circa 1944 and was inspired to copy one of the many illustrations drawn by Kate Seredy in the book, which was first published in 1939.
Plath of course learned some of her drawing skills by copying, and it is analogous to suggest she learned to write poetry in the same way: by copying. Of course there were innate skills that she brought to each art form: I'm not suggesting otherwise.
In considering the drawing reproduced in Eye Rhymes, on page 12, I thought: would it not be interesting to see what the original looked like? Fortunately a local college library holds the book so I went over there yesterday to find the source. Below is the original, and beneath, courtesy of Google Books, Plath's drawing.
Update: 17 November 2015:
Today, reading Plath's diary, I learned that this drawing was completed on Wednesday, 19 July 1944.