Question

Why do farmers set up a scarecrow in their field​

Answer 1

To scare away the birds
And in order to protect their crops

Answer 2

Answer:

A scarecrow or hay-man is a decoy or mannequin in the shape of a human, Wikipedia explains. It is usually dressed in old clothes and placed in open fields to discourage birds such as crows or sparrows from disturbing and feeding on recently cast seed and growing crops.

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