The line four calling birds is an Americanization of the traditional English wording four colly birds, and in some places, such as Australia, the variation calling is supplanting the original. Colly is a dialect word meaning black and refers to the European blackbird Turdus merula.
The line four calling birds in some versions is four coiled birds.
Religiously, The 'four calling birds' are the Evangelists: Matthew, Mark, Luke, and John; or their Gospels.
