The subspecies fujiyamae
of Northern Goshawk Accipiter gentilis
breeds in Japan, Sakhalin, and Southern Kurile Islands as an endemic subspecies (OSJ 2000). This paper shows the measurements from 64 individuals of A. g. fujiyamae
caught in central Saitama and southeastern Tochigi Prefectures, Honshu, along with the identification criteria of sex and age based upon measurements (Table 1), plumage features (Fig.1), and iris colour (Table 2). Adult males were significantly smaller than adult females for all measurements (Table 1). Tails of juveniles were significantly longer than adult tails for males (t
<0.05) and probably also for females (Table 1). We could distinguish the age as juvenile, first winter, and adult plumages based on the plumages combined with iris colour (Fig.1). A few juvenile feathers of upper and under wing-coverts remained in first winter plumage until about two years old, which was the bird's third year. Measurements from live birds tended to be larger than the data reported in the literature, which were mostly taken from specimens. The difference was as large as 10 mm in the case of tarsus length. The iris was pale yellow (sulfur yellow) in juvenile plumage and tended to acquire an orange tinge as the bird aged, mainly spectrum yellow or orange yellow in first winter plumage, and orange yellow or orange in adult plumage after in the second winter plumage. We show for the first time that the iris may turn red for old males of Japanese Northern Goshawks A. g. fujiyamae
(Table 2 and Fig. 1).