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Population dynamics and individual life of the colony-breeding Grey Heron Ardea cinerea in suburban Tokyo
http://hdl.handle.net/10748/6226
http://hdl.handle.net/10748/622638500360-4c75-4e30-b2bf-30a46dab884b
| 名前 / ファイル | ライセンス | アクション |
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T00037-001.pdf (14.3 MB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||||
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| 公開日 | 2014-03-19 | |||||||
| タイトル | ||||||||
| タイトル | Population dynamics and individual life of the colony-breeding Grey Heron Ardea cinerea in suburban Tokyo | |||||||
| 言語 | ||||||||
| 言語 | eng | |||||||
| 資源タイプ | ||||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_46ec | |||||||
| 資源タイプ | thesis | |||||||
| 著者 |
Shirai, Takeshi
× Shirai, Takeshi
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| 著者(ヨミ) |
シライ, タケシ
× シライ, タケシ |
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| 著者別名 |
白井, 剛
× 白井, 剛 |
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| 抄録 | ||||||||
| 内容記述タイプ | Abstract | |||||||
| 内容記述 | The density-dependent processes that limit the colony size of colonially-breeding birds such as herons and egrets remain unclear, because it is difficult to monitor colonies from the first year of their establishment, and most previous studies have considered mixed-species colonies. In the present study, single-species colonies of the Grey Heron (Ardea cinerea) were observed from the first year of their establishment for 16 years in suburban Tokyo. Colony size increased after establishment, illustrating a saturation curve. The breeding duration (days from nest building to fledging by a pair) increased, but the number of fledglings per nest decreased, with colony size. The reproductive season in each year began earlier and there was greater variation in the timing of individual breeding when the colony size was larger. The prolonged duration until nursing by early breeders of the colony suggests that herons at the beginning of the new breeding season exist in an unsteady state with one another, likely owing to interactions with immigrant individuals. Such density-dependent interference may affect reproductive success and limit the colony size of Grey Herons. Colonial birds have two confront problems to breed, which colonies that they attend and where they nest within the colony. In this study, the nest site selection by Grey Herons was examined. They tended to nest on the trees near the ridge of the hill. In the studied colony, the cherry (Prunus jamasakura) and oak (Quecus serrata) trees were often used. The nest height from the ground ranged from 7.8 to 22.2 m with the mean of 12.7 m. The nests were located from 42.7 to 100% of tree height with the mean of 83.1% (N=66, SD=14.0). Nesting at higher may provide safety from ground predators. The number of chicks fledged ranged 0 to 4 with the mean of 1.68 per attempted nest, and not correlated with any nest site characteristics such as nest height, tree diameter, and tree height. The effect of the horizontal distribution of nests on the breeding success was also undetected and it was unlikely that the peripheral nests were more vulnerable than the central ones. Thus, the reason why Grey Herons colonize at breeding was not explained by predation avoidance function, suggesting the other colony function of mate attraction and finding or information center to search efficient hunting sites. Site fidelity to the colony and breeding histories of individual Grey Herons were examined by intensive and long-term (9 years) observations of 50 fledglings and 19 adult birds banded with color-patterned rings. In total, 38 (76.0%) of 50 marked fledglings were never resighted in the natal colony. Of the 12 returned birds, 4 (33.3%) began to breed at 2-years-old, 2 (16.7%) began to breed at 3-years-old, 1 (8.3%) began to breed at 4-years-old, and 5 (41.7%) never bred. Two birds survived after 9 years from fledging. In total, 18 (94.7%) of 19 adult birds were resighted in the next breeding season and most of them (15/18) bred there. Birds tend to stay at the same breeding colony once they have returned. Some birds exhibited site fidelity to the breeding nest every year but others did not. Four pairs, with both birds marked, remained in a pair bond every year until one of them was lost. The number of chicks fledged per nest did not change with the age of the parent. Two broods in the same breeding season were observed in 7 (9.0%) of 78 nests, in which at least one parent was marked. The maximum number of fledglings produced by a single male over the 9 years was 22. Of 23 birds that were resident for more than 2 years, 4 birds (all females) continued to stay at the colony site after the breeding season. However, 19 (8 males, 3 females, 8 unsexed) left the colony after the late breeding season and were observed in outside locations, particularly at fixed feeding sites. The maximum distance of resighted, marked fledglings was 1,580 km southwest of the colony, 54 days after release. In Grey Heron, thus, individual behavior and performance in the colony affect the whole colony dynamics. Benefit of colony breeding in suburban Tokyo, where predation pressure is now week, may be efficient and continuous mate searching for their long lives despite being density-dependent processes in the colony when it reaches high density. | |||||||
| 抄録 | ||||||||
| 内容記述タイプ | Abstract | |||||||
| 内容記述 | サギ類は，繁殖期になると，ある特定の場所に集合して繁殖コロニーを形成する．繁殖コロニーはよく目立ち，樹上に作られた繁殖巣を直接数えることができるため，コロニーサイズの年変化やある地域でのコロニーの離合集散過程などを追跡した研究が多い．しかし，コロニー動態を明らかにするためには，各個体の挙動を調査し，そこで生じる密度依存過程や個体の行動の変化から，コロニー全体をとらえなければならない．本研究では，各個体の行動や繁殖の履歴を通してコロニーの長期動態を明らかにする目的で，東京近郊に形成されたアオサギ単独の繁殖コロニーを，創成期から16年間にわたって観察し，コロニー内の密度依存過程，コロニー内での巣場所選択，コロニー構成員の移出入を調査した．繁殖つがい数は創成期から徐々に増加し，飽和曲線を描いた．繁殖つがい数の増加にともない，各つがいの造巣から巣立ちまでの期間が長くなり，一巣あたりの巣立ち雛数が減少する傾向があった．繁殖は，毎年，初春から夏にかけて見られた．繁殖つがい数が多いと，繁殖開始時期が早まり，また，営巣開始の早いつがいほど，造巣から孵化までの期間が長くなる傾向が認められた．つまり，繁殖期初期には，その年の新規繁殖個体や他のコロニーからの移住個体などとの相互作用が頻繁になり，育雛開始が遅延するのではないかと推定された．コロニー内での巣場所選択に関しては，毎木調査を行い，樹種，胸高直径，樹高，相対的樹高（コロニー地域のもっとも低い地面から木の先端までの高さ）を営巣木と非営巣木で比較した．その結果，樹種については，ヤマザクラとコナラがよく利用されること，樹高自体ではなく，相対的樹高が高いほどよく営巣されることが明らかとなった．実際の巣は樹高の83%の位置にかけられていた．しかし，野外で見られた巣の垂直的，水平的位置と各巣の巣立ち雛数の間には統計学的に有意な関係は認められなかった．9年間については，総計50個体の巣立ち直後の幼鳥と19個体の成鳥に足環を装着して個体識別を行い，観察を継続した．幼鳥については，12個体が出生コロニーに帰ってきた．そのうち，4個体は2歳で，2個体は3歳で，1個体は4歳で初めて繁殖を行った．5個体はコロニー内にいたが繁殖はしなかった．これら12個体のうち9年後にもまだ2個体がコロニー内で見られた．成鳥はほとんど（19個体のうち18個体）が，翌年以降も引き続き繁殖コロニー内に戻った．同一コロニー内で繰り返し繁殖した場合，同じ巣場所で繁殖することもあれば，違う巣場所で繁殖することもあった．雌雄とも個体識別された4つがいの繁殖履歴を見ると，どちらかがいなくなるまでつがい相手をかえない傾向が認められた．毎年，非繁殖期（秋から冬）になると，繁殖コロニーでは見られなくなる個体が多い．そうした個体は，近辺の川沿いの決まった場所で毎年目撃される傾向があり，繁殖コロニーと非繁殖期の採餌場の移動を毎年繰り返していることが示唆された．巣立ち雛は長距離移動を行うことが知られているが，今回も，幼鳥に足環を付けてから54日後に，久米島で確認された個体がいた．アオサギは，大型で長寿である．巣立ち後は出生コロニーから分散するが，成鳥は繁殖コロニーに対して固執する傾向がある．狭い範囲に密集して営巣するため，毎年，繁殖期初期には不安定な状態が生み出され，繁殖成功度への密度依存性が顕在化すると考えられる． | |||||||
| 内容記述 | ||||||||
| 内容記述タイプ | Other | |||||||
| 内容記述 | 首都大学東京, 2013-03-07, 博士(理学) | |||||||
| 書誌情報 | 発行日 2013-03-07 | |||||||
| 著者版フラグ | ||||||||
| 出版タイプ | VoR | |||||||
| 出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||||
| その他のタイトル | ||||||||
| その他のタイトル | アオサギの繁殖コロニーの長期変動と各個体の行動・繁殖履歴 | |||||||
| 国立国会図書館分類 | ||||||||
| 主題Scheme | NDLC | |||||||
| 主題 | UT51 | |||||||
