Photo/Illutration“Tanuki” raccoon dogs inhabit Fukiage Garden, part of the Imperial Palace (Provided by the Imperial Household Agency)

Emperor Akihito collected "tanuki" raccoon dog feces from the Imperial Palace grounds over a five-year period for a research project, it has been revealed.

He studied them under a microscope, and his sheets have been compiled into a research paper titled "Long-term Trends in Food Habits of the Raccoon Dog in the Imperial Palace," which the Bulletin of the National Museum of Nature and Science published on Aug. 22.

The emperor made it a rule to visit what was branded the “toilet for raccoons” in Fukiage Garden at the Imperial Palace at 2 p.m. on Sundays from January 2009 to December 2013.

The emperor's fixed-point observation of the Japanese raccoon dogs defecation area over a five-year period is unprecedented research.

One hundred and sixty-four stool samples were collected during 261 visits to the site.

The emperor's research, in collaboration with the National Museum of Nature and Science, revealed the seasonal dietary habits of the raccoon.

It revealed that plants in eight taxonomic groups, including flowering plants such as the “muku” tree, wild berries and Chinese hackberries, are mainly eaten by the mammals.

When he was away from the palace on official duties, staff members collected samples on the emperor's behalf.

In cities it is rare to see raccoon dogs. About a thousand are believed to inhabit the 23 wards in Tokyo.

Dozens of the wild mammals inhabit the Imperial Palace site, according to the Imperial Household Agency.

The emperor is not new to studying raccoon dog feces as he published a research paper on the same subject in 2008.

(The article was written by Yasuhiko Shima and Akiko Tada.)