Bird droppings, also known as guano, are the excrement of birds. They are composed of a mixture of feces and undigested food. The term 'bird dropping' is often used to refer to the white, powdery substance that is left behind after a bird has defecated. The crossword solution for this term is 'FEATHER, ' which refers to the small, light, and fluffy structures that are found on the bodies of birds. Feathers are made up of a protein called keratin and are used by birds for insulation, flight, and protection.