Linguist Geoffrey Pullum coined the term that is defined as the mistaken substitution of one word or phrase for another word or phrase that sounds similar or identical. The speaker or writer of an eggcorn is generally not aware of the blunder.
From what I can tell, other than the St. Julian wine, there is no such thing as a red heron.
Eggcorn image via Boston.com
Red herring image via Politichicks.tv
Red heron image via redheronlampeter.blogspot.com