著者

鈴木 和博 中村 俊夫 南 雅代 池田 晃子 Suzuki Kazuhiro Nakamura Toshio Minami Masayo Ikeda Akiko

出版者

名古屋大学年代測定資料研究センター

雑誌

名古屋大学加速器質量分析計業績報告書

巻号頁・発行日

vol.22, pp.121-134, 2011-03

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Japanese Red foxes (Vulpes vulpes japonica) establish stable home ranges within particular areas or are itinerant with no fixed abode around human habitations. They are popular wild animals and feature prominently in the folklore of human culture. The population, however, was decreased until the beginning of the 1970's, and no fox has been seen since about 1975 in Kodenosawa, a small habitation about 17km NE from the urban area of Toyota City. A fox remains was found from the under floor of the Jizo-temple together with a ragged package of Nissin Chicken-Ramen which was used from 1971 to 1983. The fox's remains is c. 50 cm in body length. The left half of the remains exhibits soft tissues including skin and dried muscle, but the right half facing to the ground is completely decayed. To determine when the fox died, we measured 14C concentration in collagen extracted from a tooth and a rib of the remains. The δ13C (-18±1 ‰) normalized 14C concentrations are 129.2±0.4 pMC for the tooth and 129.0±0.4 pMC for the bone. Although the values intersect the calibration curve at 1962 and 1979, the 1979 age only agrees with the time span supported by the envelope of Chicken-Ramen. Drying of muscle tissue without rotting was likely to take place in cold winter. Thus, the fox's death is reasonably definable in the period from late November 1979 to early January 1980. The δ13C (-18±1‰) values suggest a diet containing a significant amounts of C4 food or protein with higher isotopic values. There is little C4 plants in Kodanosawa, but sizable amounts of cone were constantly brought from outside for cow's and chicken's food. A possible protein source is the herbivore and the omnivorous feeder within the area. An alternative may be marine fish and the derivatives including dog- and cat-food. To test whether the fox took food brought from outside or not, we analyzed the 87Sr/86Sr isotopic ratio of the remains. The 87Sr/86Sr isotopic ratios, 0.709439±0.000016 for the tooth and O.749464±0.000014 for the bone, are distinctly lower than those of wild boar's bone (0.709944±0.000016 and 0.709912±0.000012), river water (0.710079±0.000016) and the granite (0.710218±0.00016) that underlies the wide area of Toyota City. The initial 87Sr/86Sr ratio of 0.7096±0.0001 constrains the lowest isotopic ratio of water, plants and animals within the area. The distinctly lower 87Sr/86Sr values documents that the fox took sizable external food with higher δ13C values. After the disappearance of foxes from Kodenosawa around 1980, wild boars swelled in population. Voracious scavengers dug slope of hills side and paddy fields as they foraged for bulbs, yams, earthworms and grubs, and eventually ate voraciously paddy, sweet potatoes and beans in the field. This triggered the abandonment of cultivation of fields that face mountains. It is likely presumed that foxes were preventing wild boars from invading the human habitation through attacking Uribou, young wild boars. 愛知県豊田市小手沢町にある地蔵堂を建替えるために旧堂を取壊したとき,床下から乾潤びたキ ツネの遺骸が見つかった.遺骸の横に1971年から1983年まで使用されたデザインのチキンラーメ ンの袋があった. 口先から骨盤までの長さが約50cmの成獣である.遺骸の地面に接した右側半分 と尾は骨まで溶けて失われていた.左側半分には耳や皮膚も腐敗することなく保存されていたが, 体毛は全く残っていなかった.骨は白骨化し,前足の付け根の皮膚にのみ黒色の筋組織様のものが 付着していた. キツネの歯と骨から抽出したゼラチンコラーゲンの14C濃度(δ13C=-25‰に規格化)は129.2±0.4 pMCと129.0土0.4pMCである.この較正年代(1962年と1979 -1980) 年)とチキンラーメン袋の 使用期間および腐敗の無いことを総合して,キツネの死亡時期を1979年11月下旬~1989年1月上 旬と特定した.キツネのδ13Cは=-18±1‰である.小手沢地内にはC4植物が殆ど栽培されていない ので, 地域内の植物や小動物のみを食べていたと仮定すると,ほぼ完全な肉食をしない限りδ13C=-18‰にならない.一方,キツネの87Sr/86Sr比は0.70745 であり,分析誤差を超えて小手沢のイノシ シ(0.70993) ・川の水(0.71008) ・花崗閃緑岩の初生値(0.7096)より小さい. δ13C値と87Sr/86Sr比か ら,キツネは外来の餌(残飯を含む人間の食料やトウモロコシ主体の家畜飼料)を相当量摂取して いたと結論した. 地蔵堂の床下から見つかったキツネの死亡時期(1979年)は,小手沢地内でキツネが減少した時期 より約10年後で,イノシシの食害が顕在化する1980年代半ばに近い.人家に近い里山を縄張りと するキツネが,イノシシの人里進出を阻止していた可能性を考察した.