At eight stations in and around shrine forests in Kyushu and Tokyo metropolitan area, long-term use patterns of natural tree hollows and nest boxes by the Japanese giant flying squirrel, Petaurista leucogenys, was studied during 1972-1981, together with an experiment in captivity. The results obtained are summarized as follows: 1) The flying squirrel seemed to remember the locations of the tree hollows and nest boxes within its home range, and paid frequent visits to them at night. 2) Gnawed marks were often found at the entrance of tree hollows and nest boxes. Distribution of the marks had no relation to the use ratio of nest boxes, but this gnawing habit appeared effective in securing many refuges in the woods 3) The animal often rotated the primary nest among several nests within its home range. Duration of sttlement in a nest ranged from several days to several monthes. Occasionally, the animal mode one day\u27s lodging in one of the secondary nests which were rarely used ordinarily. 4) Nest materials were always found in both the tree hollow nests and the nest boxes in which the animal settled for several days, although an animal might lodge for only one day even in the nests devoid of the materials. 5) The same individual was never found in a given nest over two years. Thus, the home range seemed to shift within two years at the longest. 6) A given nest was used by several individuals one after the other except for a mother and her young. An animal which had returned to a nest befor others had priority and prevented an invader from entering it. 7) Captive individuals also refused to lodge with a stranger, but accepted it in daytime probably because of a decline of the activity. 8) Intra- or inter-specific competition for a nest and occurrence of external parasites in a nest seemed to be external factors causing the shift of nest. A rainfall in the nighttime made the animal take a secondary shelter nearby. 9) Even after becoming independent, young still lived together their mother with repeated separations for several months. 10) The use ratio of tree hollow nests which had been utilized for many years averaged 32% (7-64%) which showed roundly almost no regional difference. 11) The use patterns of nest boxes at Okawachi was similar to that of the tree hollow nests at other areas in that they were used as primary nests by a certain individual for lodging consecutively to some extent. On the other hand, at Hikosan Biological Laboratory (HBL), only adult males used boxes, and then mainly as secondary nest. These males had wider home ranges than females, and the males invaded the study area at the periphery of their ranges. 12) The mean use ratio of nest boxes was 0.7% at HBL (60 boxes) and 5.4% at Okawachi (24 boxes). At HBL big trees are fewer than at neighboring areas, and the flying squirrels appeared to use the site only as feeding sites at night and to move to adjoining areas to rest in daytime; accordingly, the boxes did not facilitate an increase of the number of individuals. 13) The use ratio of nest boxes at HBL became relatively high during the period of May to September. Frequent changes in nest by males sexually active, or the shift of home range owing to the seasonal change of food items seemed to be the main cause of such a fluctuation in use ratio.九州及び東京都の社寺林を主体にした8地点において，ムササビ Petaurista leucogenys の長期的な巣穴利用性を知るために，1972～1981年にかけて，天然巣穴の観察，新たに架設した本種誘致用巣箱の利用性に関する調査及び飼育実験を行った．結果は次のとおりである．1）ムササビは行動圏内にあるいくつもの樹洞や巣箱の位置を正確に認知しているようで，平常の夜間活動中にそれらを特定の「立ち寄り場所」として頻繁に訪れた．2）樹洞や巣箱の出入口にはしばしば齧り跡が認められた．巣箱の利用率と齧り痕の出現頻度との間には相関は認められなかった．この齧り行動は森林内に避難可能な場所を常に多数確保するのに有効な行動と考えられる．3）本種は行動圏内にある複数個の巣穴の間でしばしば定住場所を替え，1ヵ所に定住する期間は短い場合には数日，長い場合には数か月に及んだ．時には，平常あまり用いない場所に1日だけ臨時的に宿泊することもあった．4）定住場所として使われた巣箱では，例外なく巣材が認められたが，1日だけの宿泊は巣材のない場所でも行われた．5）同一個体が2年以上に亘って同じ巣穴で発見されたことはなかった．このことから本種の行動圏は長くても2ヵ年位で変化すると推測される．6）ある1つの巣穴は数頭の個体によって交互に共用されていた．すなわち，宿泊は母仔の場合を除いて，四季を通じて単独で行われることが多かった．この原因として，先に巣穴へ帰巣した個体が遅れてそこへ入ろうとする個体を攻撃し，同居を拒否することが挙げられた．この場合，先入個体が常に優位であった．7）飼育下においても本種は見知らぬ個体との同居を拒否した．しかし，昼間には活動が低下するためか，このような攻撃は起こらなかった．8）巣の変更をもたらす外的要因として，種内あるいは種間の巣穴をめぐる競合と巣内における外部寄生虫の発生などが挙げられた．夜間の降雨は本種を臨時の巣穴へ避難させた．9）母仔は巣立ち後も更に数ヵ月間の同居を続けるが，その間に頻繁に集合と離散が繰り返された．10）長年に亘って使用が確認されている樹洞巣穴の利用率は平均32％（7～64％）であった．樹洞巣穴利用率における地域差は小さかった．11）巣箱を架設した2地点のうち，大河内の巣箱は定住場所として利用されたという点において，他地域の樹洞巣穴利用パターンと類似していた．他方，実験所の巣箱では1日だけの宿泊が大部分を占め，しかも宿泊個体の殆どが雄成獣である点で特異的であった．この原因として，隣接の社叢に定住巣穴を有するムササビのうち，雄だけが調査方形区を包含する広い行動圏を持ち，巣箱を臨時の宿泊場所として用いていたことが考えられる．12）実験所に架設した巣箱（60個）の平均利用率は0.7％，大河内のそれ（24個）は5.4％であった．実験所では巣箱への定住例が少なく，ひいては巣箱設置による個体数増加は認められなかった．これはムササビが高木の多い森を好み，相対的に低木の多い実験所の敷地を夜間の採食場としてだけ利用したためと思われる．13）実験所の巣箱利用率は5月～9月に比較的高くなった．その理由として，発情期の雄は頻繁に臨時の巣穴へ宿泊すること，あるいは餌の存在場所の季節的変化に伴って本種が行動圏を変化させることなどが考えられる
