Merle

I do not think that Merle is a form of Merrill or Muriel. I think it is instead transferred from the French surname Merle, which did mean "blackbird" and may have been a nickname in medieval France for someone who often whistled, or for some other characteristic attributed to blackbirds. According to Hanks & Hodges, at different times and places in medieval Europe blackbirds were thought to be either foolish, or the opposite, very shrewd. The first examples of the use of Merle as a given name in the United States are found in the 1850 census in New Orleans, a city where many residents had French ancestry, reinforcing the idea that it's from the French surname. Merle was almost never a girls’ name before 1880. That year, Henry James published his most popular novel, “The Portrait of a Lady.” One of its main characters was Madame Merle, the American-born widow of a Frenchman. Though her first name is Serena, that’s mentioned only once in 767 pages. In any event, its use as a girl's given name is probably from this novel and so is also from the French surname. [noted -ed]