Ottoman Birdhouses

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The Ottomans had a tradition of adding birdhouses to their public buildings. From Colossal Art's The Ornate Bird Palaces of Ottoman-Era Turkey:

"... providing shelter to sparrows, swallows, and pigeons while preventing bird droppings from corroding the walls of the surrounding architecture. In addition to providing shelter, the birdhouses fulfilled a religious vision. They were thought to grant good deeds to those that built the tiny homes."

You read mead more about them, as well as see a few more pictures, at the Colossal link.