A scarecrow was a person who used to be employed to scare away birds from the fields that were newly planted with seeds. They would sing songs like this one…

The Scarecrow - English Children's Songs - England - Mama Lisa's World: Children's Songs and Rhymes from Around the World  - Intro Image
The Scarecrow - English Children's Songs - England - Mama Lisa's World: Children's Songs and Rhymes from Around the World  - Comment After Song Image

Thanks and Acknowledgements

The illustration is from The Baby's Bouquet, A Fresh Bunch of Rhymes and Tunes by Walter Crane (1878).