A scarecrow is a device posted on cultivated ground to deter birds or other animals from eating or otherwise disturbing seeds, shoots, and fruit; its name derives from its use against the crow. The scarecrow of popular tradition is a mannequin stuffed with straw; free-hanging, often reflective parts movable by the wind are commonly attached to increase effectiveness. A scarecrow outfitted in clothes previously worn by a hunter who has fired on the flock is regarded by some as especially efficacious. A common variant is the effigy of a predator (e.g., an owl or a snake).

Source: Britannica