NEW PRINCESS ATTACKS GRIFFONSTAN IMPORTS

The Equestria Daily can exclusively report that newly crowned Princess Twilight Sparkle became embroiled in an argument with the Griffonstani trade minister about the inferior quality of griffon quills, alleging that "they just don't hold ink as well as pegasus quills". Import markets tumbled overnight, threatening the solvency of numerous Equestrian quill merchants. Princess Sparkle could not be reached for comment.

(When you're done, bookplayer has a fun "Let's Read" commentary version!)
(Also, GhostOfHeraclitus wrote a prequel from the perspective of Dr. Spinning Top!)
(Also also, now available in Spanish thanks to Spaniard-Kiwi!)

Mood Wings - Observations on Pegasus Body Language.

When Twilight Sparkle finds this book, she discovers an entirely new field of research. The secrets of pegasus wings lie before her, and she insists on making her own observations on the matter.

How?

Field research, of course.

This story is a sequel to Petriculture

It's been several months since Pinkie Pie made a stunning admission about her past that permanently changed her relationship with her friends, particularly Twilight Sparkle, but life seems to have settled back to normal (well, normal by Pinkie Pie's standards, at least). However, when an old nemesis returns and ensnares Twilight in her influence, it's up to Pinkie to make things right.

This is the second story in The Petriculture Cycle. There is a TV Tropes Page for the entire Cycle here.

Cover image by Page Turner; "Princess Twilight" vector by Nianara.