The wagtails form the passerine bird genus Motacilla. They are small birds with long tails which they wag frequently. Motacilla, the root of the family and genus name, means moving tail. The forest wagtail belongs to the monotypic genus Dendronanthus which is closely related to Motacilla and sometimes included herein.The willie wagtail (Rhipidura leucophrys) of Australia is an unrelated bird similar in coloration and shape to the Japanese wagtail. It belongs to the fantail flycatchers.