Any guesses?

A couple of weeks of ago we discovered a small irregular shape/smudge on the outside of one of the glass doors facing the pond in our living room. Giving no thought to what it might be, my wife cleaned the doors and the 'blemish' was gone.

This morning, I noticed a similar shape and went for the camera. On closer inspection, the shape is made up of extremely small, perfectly round little clear dots. It measures about 1" in width by 1/2" in height. It shows up as dark dots in the picture. I was in auto macro mode explaining exposure and the out-of-focus trees/sky in the background.

WHAT, PRAY TELL, COULD THIS BE? Insect or bird deposit? It is a puzzlement!