Fence Climbing Behaviour of Raccoon Dogs (nyctereutes Procyonoides): Assessing Their Risk at Highways

27 Mar Fence Climbing Behaviour of Raccoon Dogs (nyctereutes Procyonoides): Assessing Their Risk at Highways

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Abstract

タヌキ（Nyctereutes procyonoides）がフェンスを通過するために試みる行動を明らかにすることを目的として，2010年10月18日から2010年11月7日まで，捕獲したホンドタヌキ（N. p. viverrinus）3頭のフェンスに対する行動を実験装置において撮影および分析した．フェンスの素材として，高速道路において一般に設置されている菱形金網（高さ150 cm）を用い，上部には乗り越え防止装置を2種類（塩化ビニル板，トリカルネット）施した．掘削（成獣オス）や乗り越え（当年仔）により通過の成功が観察されたが，トリカルネットが張られているフェンスでは成功しなかった．トリカルネット，塩化ビニル板それぞれに対し，噛みつく，上方へ前肢を伸ばす，上方へ体を伸ばす行動がみられた．2011年10月から2012年10月の東京農工大学農学部キャンパスおよびFM多摩丘陵，東京都日の出町大久野付近の捕獲個体7頭の計測から，フェンスの網目の幅が前後肢の掌幅の最小値27 mmを下回ればフェンス上に留まることができないと考えられ，下顎の横幅12.4 mm以下であれば犬歯の位置まで顎を網目に入れられないためフェンスに噛みつくことができないと考えられた．前肢の前後方向への開きは最大53.6 cmであったことから，乗り越え防止装置の高さはそれ以上であれば前肢や体を伸ばしてもフェンス頂上に届かないと考えられた．

English Abstract

Between 18th October and 7th November 2010, three raccoon dogs were captured in Field Museum Tamakyuryo (FMT), and behaviour at fences was recorded by IP cameras at an enclosure. In this enclosure, fencing constructed of diamond-mesh wire netting, 150 cm in height, was used in conjunction with two types of mitigation commonly used in highway fences to prevent raccoon dogs from climbing (PVC board, Trical net). The raccoon dogs escaped successfully by both digging under (adult male) and climbing over the wire fence (yearling), but were not able to climb over the Trical net. Attempts to circumvent the mitigation treatments included biting, stretching the forelegs and/or stretching the nose upwards with standing on rear legs and pawing at the fence. Between October 2011 and October 2012, seven wild raccoon dogs were captured and measured at the TUAT campus, FMT, and Hinode town. These had a minimum paw width of 27 mm, indicating the largest fence mesh size capable of preventing them from climbing the fence. Their minimum lower jaw and canine width was, however, 12.4 mm, and therefore they were able to bite onto even this small Trical net mesh size of. Thus, maximum Trical net mesh size appears to be within 12.4 mm for purpose of bite-proof by raccoon dogs. The maximum gap between the forelegs was 53.6 cm, therefore PVC prevention board larger than this should not be scalable by raccoon dogs.