Notice the identical eyes, blacks heads, brown arms, and similar feet. These are clearly a series. They are also all stamped "Japan" in green with identical 5 and 3 pour hole pattern. Circa 1950s-60s. This appears to be a complete series with only 4 pairs of shakers.
Originally referenced in The Big Book of Salt & Pepper Shaker Series by Irene Thornburg on pages 85-86 in 1999.