Though entirely unrelated to birds, pegasi have been known to exhibit behaviours and habits that would be familiar to ornithologists.
Though it would not always be apparent, and indeed would often be shown in the most oblique of ways, Big Macintosh would find that his relationship with Rainbow Dash would provide good case studies to demonstrate this.
Blame Captain Unstoppable. For it is always his fault. Enjoy the MacDash fluff that is his fault.