I saw this in the paper birch tree at the town hall.
It probably is a hummingbird nest.
My camera extends from 4 to 180 mm.
Without extending the lens, the nest seems like some debris caught in the branches.
Hummingbirds generally do not reuse nests, but recycle them.
(Thank you, Google.)
The windows behind are in a room that is locked unless rented for an event,
but I'll try and keep an eye on the nest from the lower level, where I am. Until it disappears into the leaves.