Namely Gerald Durrell's My Family and Other Animals and Charles Darwin's Voyage of the Beagle.

The result was a oneshot I wrote called Gallopagos. Discord tells Fluttershy a mostly non-fiction story of his time there. Mostly.

Any other classic nature/non-fiction literature you enjoy?

I once read a study on different species of sharks and venomous creatures but I don't remember how old it was nor the titles so I wouldn't be able to tell you whether it was considered classical or not.