A mysterious howling marked the start of Hiroshi Yagi's 40-year search for an animal that has not been seen in Japan for more than a century.

He has switched jobs, set up sophisticated monitoring equipment, climbed mountains and trekked through forests all in hopes of finding the Japanese wolf.

The Japanese wolf, described as having a sharp face and a curled tail tip, is an extinct species on the Japanese Red List of the Environment Ministry. It was hunted mercilessly by humans, fell victim to infectious diseases and saw its habitat wiped out by development.

The Japanese wolf is still worshipped as a guardian god in some regions of Japan because they attacked deer and wild boars that were ruining farmland.

Until the Meiji Era (1868-1912), the Japanese wolf inhabited wide areas of Japan's mainland, as well as the Shikoku and Kyushu regions.

But the Meiji government regarded the Japanese wolf as a threat to livestock, and ordered its extermination, according to experts.

The last time a Japanese wolf was caught was in 1905 in Higashi-Yoshino, Nara Prefecture. There have been no confirmed sightings since then.