An important element of Ottoman architecture in Turkey was the addition of birdhouses affixed to the outer walls of significant city structures, a safe space for regular avian guests to nest outside of mosques, inns, bridges, libraries, schools, and fountains. The birdhouses were not simple concrete structures, but rather elaborate feats of miniature architecture that ranged from one-story homes to multiple-story bird mansions. Each was designed with a similar design aesthetic to the country’s larger buildings, simultaneously providing shelter to sparrows, swallows, and pigeons while preventing bird droppings from corroding the walls of the surrounding architecture.

Source: The Ornate Bird Palaces of Ottoman-Era Turkey