We know in Brittany the great debate that agitates the breton speakers of neighboring communes concerning the difference of their speeches to the point of affirming that they do not understand each other. It is to ignore how fruitful the popular imagination has been, creating here and there terms specific to one place or another. Some of them have often spread over large spaces according to oral transmissions. Others, on the contrary, took place only on smaller perimeters. This article, both linguistic and ethnographic, shows precisely the mechanisms of popular creation about ornithonymes with comparisons in Celtic countries.