Volume 7 (2011) Pages A33-A44
Pericrocotus divaricatus tegimae is a subspecies of the Ashy Minivet in Japan. The recent distribution of P. d. tegimae in western Japan was estimated based on a literature survey and questionnaires conducted in 2010. In the 1970s, the distribution of P. d. tegimae was limited to southern Kyushu. Since 2010, P. d. tegimae has been recorded throughout the entire island of Kyushu, a part of Shikoku, and on Honshu at the Kii Peninsula. A part of P. d. tegimae population seems to move to warmer and/or lower altitude sites in winter than they inhabit during the summer. Most of them, however, stay as resident breeders in their particular locations.
The comparison of habitat factors associated with the two subspecies in Japan, P. d. tegimae and P. d. divaricatus, such as altitude, temperature and vegetation type, revealed the similarity of their habitat niches. The distribution of the two subspecies in Japan is complicated in that P. d. divaricatus breeds in a more northern region of Japan than P. d. tegimae, whereas P. d. tegimae stays in Japan's temperate regions during winter when P. d. divaricatus makes a long-distance migration to overwinter in tropical regions. This type of distribution is not explained by differences of physiological characteristics. The decline of the P. d. divaricatus population in the 1980s has probably created a niche vacancy for minivets, which provided an opportunity for P. d. tegimae to expand its range as a resident in southern to central Japan. An estimate of the potential distribution of minivets, limited by snowfall, temperature and vegetation, shows that the habitable area for P. d. tegimae reaches the Kanto region of Honshu.