Singer Sewing Machine 1920's Advertising Cards - American Song Birds

This is a set of advertising cards put out by The Singer Sewing Machine Company, dated 1926, '27, '28, '29. They are each 4 1/2" x 6" and printed on fairly thin stock. Each one has a lovely bird illustration by J. L. Ridgway, a well known science and ornithological artist. The back of the card has information about the particular bird and an ad for some aspect of the Singer Sewing Machine empire.
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