From the fantastic resources blog "2 Teaching Mommies" this is part of a whole scarecrow unit available for download here.
Click on the image on their blog post to download all the resources in one zip file. The size sort is one single pdf - the first page is the scarecrow and birds, the second is a sorting mat for "small" "medium" and "big". If yours is a littler tot (B falls into this category for some tasks!) there is a related tot pack to download further down the same post. Great for a farm or autumn theme as well.