These birds start breeding in late February and some of the males were already singing. Unlike the more common White Wagtail, this species keeps the same plumage year-round. The sexes are similar with the male being solid black on its back and the female with a slight grayish tinge as seen here. This distinctive species is endemic to Japan but some migrate to South Korea. White Wagtails have been expanding their range in Japan in recent decades, but their expansion has not impacted the Japanese Wagtails which seem to prefer wetter habitats. Canon PowerShot SX60
References:
Alström, P. & Mild, K. (2003) Pipits & Wagtails of Europe, Asia and North America. Identification and Systematics. Christopher Helm, London.
Tyler, S. (2019). Japanese Wagtail (Motacilla grandis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/57823 on 29 March 2019).