A scarecrow is a device – traditionally a human figure or mannequin dressed in old clothes – placed in fields by farmers to discourage birds such as crows or sparrows from disturbing and feeding on recently cast seed and growing crops
In Kojiki, the oldest surviving book in Japan (compiled in the year 712), a scarecrow known as Kuebiko appears as a deity who cannot walk, yet knows everything about the world.
The 1881 Household Cyclopedia of General Information gives the following advice:
Machinery of various kinds, such as wind-mills in miniature, horse rattles, etc., to be put in motion by the wind, are often employed to frighten crows; but with all of these they soon become familiar, when they cease to be of any use whatever.The most effectual method of banishing them from a field, as far as experience goes, is to combine with one or other of the scarecrows in vogue the frequent use of the musket. Nothing strikes such terror into these sagacious animals as the sight of a fowling-piece and the explosion of gun powder, which they have known so often to be fatal to their race.
Such is their dread of a fowling-piece, that if one is placed upon a dyke or other eminence, it will for a long time prevent them from alighting on the adjacent grounds. Many persons now, however, believe that crows like most other birds, do more good by destroying insects and worms, etc., than harm by eating grain.—Henry Hartshorne, The Household Cyclopedia of General Information
Crows can be a substantial problem for gardens in the springtime: they can work down a row pulling up recently sprouted corn to eat the remaining seed/seedlings. In the southern Appalachians another common method of scaring off crows was use of a dead crow hung upside down from a pole.
Modern scarecrows seldom take a human shape. On California farmland, highly reflective aluminized PET film ribbons are tied to the plants to create shimmers from the sun. Another approach is automatic noise guns powered by propane gas.