One morning while my little Miss Abby was perched atop the back of an overstuffed chair which happens to be up against a sliding glass door...there was all of a sudden a huge BANG!
I came running into the family room thinking it sounded like my son might have walked through the sliding glass door (that's how loud it was!) but, soon discovered that a Hawk had been sitting up on our neighbors roof spying on poor lil' Miss Abby.
My son was actually observing this Hawk when he said it just swooped in for the kill...but, the dumb Hawk didn't realize there was a sliding glass door between them!
Miss Abby weighs about 9 lbs but, with the wing span on that Hawk it could have probably easily snatched her up if she'd been lying on the lawn sunbathing herself.
From then on...all our Yorkies are supervised while in the yard. They really hate it too... especially, when they need to do their #2 business (hahaha) and all eyes are on them
So, from our experience...I'd say NEVER leave your Yorkie unattended outside even on a balcony (covered or not).

are an easy snack for a Bird of Prey!