西点林鸮学名Strix occidentalis,Spotted owl)长43厘米,翼展114厘米及重约600克。鸟蛋长约5厘米,呈白色,表面光滑。雌鸟会负责孵化及照顾幼鸟,而雄鸟则会觅食。幼鸟的平均生存率为11%,平均出生率为每对有0.58只幼鸟。西点林鸮有3个亚种,包括北方斑点鸮、指名亚种及墨西哥西点林鸮吉拉荒野保护区墨西哥亚种最大群落的家园。[2]西点林鸮的外观像横斑林鸮,但下身的斑纹呈交叉状。横斑林鸮的身型较大及较灰色。指名亚种及北方斑点鸮近年受到横斑林鸮的取代。[3]虽然两者是会混种,但其基因却很独特。[4]

西点林鸮
=
科学分类 编辑
界: 动物界 Animalia
门: 脊索动物门 Chordata
纲: 鸟纲 Aves
目: 鸮形目 Strigiformes
科: 鸱鸮科 Strigidae
属: 林鸮属 Strix
种:
西点林鸮 S. occidentalis
二名法
Strix occidentalis

分布

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北方斑点鸮的分布地由英属哥伦比亚西南部经华盛顿州西部及俄勒冈州加利福尼亚州中北部海岸的马林县[5][6]指名亚种与北方斑点鸮的分布地在喀斯喀特山脉南部重叠A,向南延伸至内华山脉

植物群落

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北方斑点鸮生活在华盛顿州喀斯喀特山脉东部的西黄松黄杉属森林,与及加利福尼亚州西北部黄杉属及常绿硬木森林。[7][8]在大部分的分布地中,它们会站在黄杉属[8][9][10][11][12][13][14][15]西部铁杉[8][11][12][13][14][15][16][17]北美乔柏[12][14]巨冷杉[8]太平洋银冷杉[11][13][17]西加云杉[8][13]加州红木[8][10][18]之上。

指名亚种会生活在硬木及针叶林。已有栖息的针叶林包括针叶混林[19]、加利福尼亚州的紫果冷衫[19]及西黄松和杰弗里松[19]加洲月桂树[19]、西黄松[19]峡谷栎[19]都是指名亚种所使用的硬木针叶混林。它们会栖息在河岸[5][19]橡树的硬木林地。[5][20][21][22]

墨西哥西点林鸮栖息在多种不同的环境。西黄松、甘比耳氏栎[23][24][25][26]及以黄杉属和科罗拉多冷杉[5][23][26][27][28]为主的针叶混林都是它们栖息的地方。在亚利桑那州,它们会选择西黄松及甘比耳氏栎[29];而在新墨西哥州的则会喜欢针叶混林。亚利桑那州大部分的繁殖地都是针叶混林或松栎的环境,但也有一些群落生活在常绿林地。[26]松属刺柏属林地可以提供非繁殖的栖息地。[5][25][27][28]不过,在新墨西哥州的群落则会避开这些环境。其他的林地包括河岸林地[23][27][28]、橡树林地[25]、松树林地[5][25]、及绿干柏林地。[25]山区草坪也可以作为觅食的地方。山区及沙漠丛林可以让幼鸟及迁徙的成鸟作为过冬的地方。[28]

生命阶段

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迁徙

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虽然西点林鸮并非候鸟,但个别也会在冬天及繁殖季节迁徙一后短距离。[5][9]迁徙的指名亚种会于10月至12月离开其繁殖地,并于2月至4月中回来。在亚利桑那州新墨西哥州科罗拉多州犹他州墨西哥西点林鸮则会在11月及12月离开繁殖地,待1月至4月才回来。迁徙中的西点林鸮会栖息在一般认为并不适合其生活的环境。[5]

繁殖循环

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西点林鸮的繁殖季节介乎初春至夏末或秋天。繁殖期的西点林鸮会于2月或3月出现一些产前行为,包括起舞及一同栖息。在俄勒冈州西部的群落会于3月9日至4月19日间生蛋。[30]它们需要30日来孵蛋,雏鸟会于4月8日至5月20日间出生。雏鸟到了34-36天大就会独立,并于9月至10月间开始离开。[30]亚利桑那州中北部的墨西哥西点林鸮由换羽至独立需要87-101天[31],并于8-10月间开始离巢。[26][31]指名亚种的离巢期各有不同。

繁殖输出

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西点林鸮是一夫一妻制[5][32],若未能成功繁殖也很少会重新筑巢。[5]它们每次会生1-3只蛋。

西点林鸮的繁殖输出各有差异。在加利福尼亚州西北部的群落,每年的繁殖输出为每对0.15-0.81只雏鸟。[7]而年内产最少1只雏鸟的比率为0-80%。[33]一项研究指在加利福尼亚州的北方斑点鸮及指名亚种在8年间的换羽率就介乎0-100%。[34]而在内华达山脉南部的群落,其每年繁殖率为每对0.07-1.67只雏鸟。[20]

多种因素都会令它们的繁殖输出出现差异,例如它们并非每年也会繁殖。[30]俄勒冈州西部,繁殖期的北方斑点鸮占了平均的62%。[30]另一种因素是它们的年龄。西点林鸮一般要到3岁才会繁殖,但也有1岁就会繁殖的。[30][35]华盛顿州及俄勒冈州,大部分的西点林鸮都是在2岁时配对。[35]由1岁大的西点林鸮所生的雏鸟比率为0.074只;两岁的是0.208只;3岁的则是0.372只。[36]地盘特征是另一个会影响繁殖输出的因素[16][37][38],栖息在较高海拔的北方斑点鸮的出生率会较低。[16][39]气候食物是最为影响它们繁殖的因素,于繁殖期间的低雨量及温暖天气可以帮助它们繁殖。[7][20][40]

分散

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幼鸟会于夏末或秋天离巢。俄勒冈州华盛顿州北方斑点鸮会于10月-4月间在过冬地点栖息,之后再分散到繁殖地。一些是会留在繁殖地,另一些则会只待到2-5岁。[35]大部分西点林鸮只会迁徙少于30公里。[28][31][35]只有8.7%的北方斑点鸮是会迁徙多于50公里。

有时成鸟会迁出其地盘。每年在俄勒冈州及华盛顿州就有6.6%的北方斑点鸮是会迁徙的。雌鸟、3-4岁大的成鸟及没有交配的个体最有可能是会迁徙的。成鸟平均的迁徙距离炭6.14公里。[35]

寿命

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西点林鸮很长寿,可以活到16-17岁。[41]成鸟的存活率每年为80%[7][42][43]

幼鸟及亚成体的存活率比成鸟的为低及不稳定。[36][42][43][44]北方斑点鸮幼鸟的每年存活率为21-29%。[43]墨西哥西点林鸮的每年存活率为64.4%。[42]

西点林鸮的致死原因是受到掠食及饥饿。[35][38]68%的北方斑点鸮幼鸟死于掠食,26.2%则是饥饿而死。[35]墨西哥西点林鸮的成鸟及幼鸟也是死于饥饿及被掠食。[38]幼鸟也会曝晒而死。[5]意外也会是致死的原因。67%的北方斑点鸮是死于其他原因,包括疾病等。[35]

食性

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西点林鸮是夜间活动的,有时也会在日间觅食。它们会停留等待猎物出现,并俯冲捕猎,也会在树穴抓食。它们会捕猎昆虫蝙蝠[9]

食性可以影响西点林鸮的繁殖输出。在加利福尼亚州,繁殖期间的猎物大小明显较非繁殖期的大。[34]

西点林鸮的猎物一般都包含哺乳动物,包括鼯鼠暗足林鼠丛尾林鼠墨西哥林鼠北方鼯鼠就占了墨西哥西点林鸮[30][45]及指名亚种[46]30%以上的食物。林鼠属也是3个亚种的主要食物。它们也会吃其他的哺乳动物,包括白足鼠属[26][30][45][46][47][48][49]平齿囊鼠属[30][45][46][47][48][49]田鼠属[30][45][46][48][49]白靴兔[45]林兔[30]赤树䶄[30][47]

非哺乳动物的猎物包括鸟类两栖类昆虫。鸟类猎物包括细小的猫头鹰啄木鸟等。昆虫只占了它们食物的很少部分。[45][46][47][48][49]它们很少会吃两栖类及爬行类[45][46][49]

掠食者

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鸟类哺乳动物(如渔貂)会掠食西点林鸮的鸟蛋及幼鸟。[5][35]苍鹰乌鸦会掠食幼鸟,而大雕鸮红尾𫛭金雕则会掠食幼鸟及成鸟。[5][30][35]大雕鸮及横斑林鸮会与它们竞争食物及地方。[50]横斑林鸮影响着北方斑点鸮在某些地区的生存率。[44]

保育状况

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北方斑点鸮墨西哥西点林鸮的群落在美国都列为濒危。北方斑点鸮的数量正在大幅下降,每年约有50%的群落在北边消失。在英属哥伦比亚现存就只有少于30对,估计在未来几年就会从加拿大绝迹。[51]指名亚种并未出现濒危情况,不过,它们正受到密切注视。

西点林鸮的所有亚种一直都是保育人士及伐林业或发展商之间的磨心。于2008年2月,在亚利桑那州犹他州科罗拉多州新墨西哥州就有34800平方公里订定为猫头鹰的栖息地。这个决定受到畜牧业的挑战,但最终得以维持。这些栖息地的订立可以确保美国的伐林并不影响鸟类的复苏。[52]

参考文献

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