武蔵学園に生息するタヌキの外食率を探る―東京都区部の狭い孤立林内の二つのため糞から出現した種子と人工物に注目して―

Abstract

東京都練馬区の狭い孤立林である武蔵学園(7.8ha)に生息するホンドタヌキの食性を糞分析で調べた。糞分析の結果，6種類の種子(エノキ，マメガキ，センダン，ムクノキ，カキノキ，ウリ科)と，布製の紐やイヤホン，布片，人工芝などの人工物が出現した。糞から出てきた種子のほとんどは学園構内で結実している樹木であったが，カキノキは構内には生えていなかった。このことは，武蔵学園のタヌキが明らかに構外に出て採食していることを示している。ただし，糞から出てきた種子の中でカキノキの割合は4%と低かった。従って，ため糞場を利用したとされる秋から冬にかけては，狭い孤立林であっても武蔵学園内で採食のほとんどを賄うことが可能だと考えられた。また，一般にタヌキが好むとされるイチョウは構内に群生しているものの糞からは見つからなかった。

We investigated the food habits of raccoon dogs living on the Musashi Academy Campus (7.8 ha), which has a small isolated forest, in Nerima Ward, Tokyo, by analyzing seeds and artificial materials found in the fecal piles of two different latrine sites on campus. The fecal analyses found six kinds of seeds (Celtis sinensis, Diospyros lotus, Melia azedarach, Aphananthe aspera, Diospyros kaki and Cucurbitaceae) and artificial materials such as shoe straps, an earphone, a piece of cloth and artificial grass. Based on the fecal analyses, we also estimated the behavioral pattern of the raccoon dogs by identifying the location, in and around the study area, of the trees bearing the seeds under investigation. Most of the fruit trees bearing the seeds are within the campus, while Diospyros kaki is not. This indicates that the raccoon dogs go in and out of the campus, and also that they get some food outside the campus. However, the proportion of seeds of fruits eaten outside the campus was as low as 4%. This means that most of the fruits that the raccoon dogs ate were from the trees on campus, suggesting that, from autumn to winter, the campus can provide the raccoon dogs with most of their diet even though it only has a small isolated forest. In addition, although there are a number of ginkgo trees (Ginkgo biloba) planted on campus, ginkgo seeds, which are generally considered to be raccoon dogs' favorite, were not found from the feces.