Black-throated Loon

Black-throated Loon Gavia arctica

Common, mainly winter visitor around Hokkaido, Honshu, Shikoku and Kyushu. 
Perhaps the Pacific side population fewer than Sea of Japan side.

Fig. 1. Adult. Molting summer plumage.
Fig. 2. Adult. Same bird as Fig. 1.
Fig. 3. Presumed Adult winter.
Fig. 4. Juvenile.
Fig. 5. 1st winter to summer. This bird has pale feather fringes on upper coverts.
Fig. 6. 1st winter to summer. Same bird as Fig. 5.
Fig. 7. 1st winter.
Fig. 8. Juvenile.