Vander Haegen W Matthew
Washington Department of Fish and Wildlife, 600 Capitol Way North, Olympia, Washington 98501, USA.
Ecol Appl. 2007 Apr;17(3):934-47. doi: 10.1890/06-0990.
Shrubsteppe communities are among the most imperiled ecosystems in North America as a result of conversion to agriculture and other anthropogenic changes. In the Intermountain West of the United States, these communities support a unique avifauna, including several species that are declining and numerous others that are of conservation concern. Extensive research in the eastern and central United States and in Scandinavia suggests that fragmentation of formerly continuous forests and grasslands adversely affects reproductive success of birds, yet little is known of the potential effects on avian communities in Western shrublands. I used multi-model inference to evaluate the potential effects of local and landscape variables on nest predation and brood parasitism, and behavioral observations of color-banded birds to evaluate the potential effects of habitat fragmentation on seasonal reproductive success of passerines in the shrubsteppe of eastern Washington State, USA. Reproductive success of shrubsteppe-obligate passerines was lower in landscapes fragmented by agriculture than in continuous shrubsteppe landscapes. Daily survival rates for nests of Brewer's Sparrows (Spizella breweri; n=496) and Sage Thrashers (Oreoscoptes montanus; n=128) were lower in fragmented landscapes, and seasonal reproductive success (percentage of pairs fledging young) of Sage Sparrows (Amphispiza belli; n=146) and Brewer's Sparrows (n=59) was lower in fragmented landscapes. Rates of parasitism by Brown-headed Cowbirds (Molothrus ater) overall were low (4%) but were significantly greater in fragmented landscapes for Brewer's Sparrows, and parasitism resulted in fewer young fledged from successful nests. Simple models of population growth using landscape-specific fecundity and estimates of adult survival derived from return rates of banded male Sage Sparrows and Brewer's Sparrows suggest that fragmented shrubsteppe in Washington may be acting as a population sink for some species. Immediate conservation needs include halting further fragmentation of shrubsteppe, restoring low-productivity agricultural lands and annual grasslands to shrubsteppe where possible, and convincing the public of the intrinsic value of these imperiled ecosystems.
由于转变为农业用地以及其他人为变化，灌丛草原群落是北美最濒危的生态系统之一。在美国西部山间地区，这些群落拥有独特的鸟类群落，包括几种数量正在减少的物种以及许多其他受到保护关注的物种。在美国东部和中部以及斯堪的纳维亚进行的广泛研究表明，以前连续的森林和草原的碎片化对鸟类的繁殖成功率产生不利影响，但对于西部灌丛地鸟类群落的潜在影响却知之甚少。我使用多模型推断来评估局部和景观变量对巢捕食和巢寄生的潜在影响，并通过对彩色环志鸟类的行为观察来评估栖息地破碎化对美国华盛顿州东部灌丛草原中雀形目鸟类季节性繁殖成功率的潜在影响。与连续的灌丛草原景观相比，因农业活动而碎片化的景观中，专性栖息于灌丛草原的雀形目鸟类的繁殖成功率较低。在碎片化景观中，布鲁尔麻雀（Spizella breweri；n = 496）和艾草䳭（Oreoscoptes montanus；n = 128）巢穴的每日存活率较低，而在碎片化景观中，艾草雀（Amphispiza belli；n = 146）和布鲁尔麻雀（n = 59）的季节性繁殖成功率（幼鸟出飞的配对百分比）也较低。褐头牛鹂（Molothrus ater）的寄生率总体较低（4%），但在碎片化景观中，布鲁尔麻雀的寄生率显著更高，且寄生导致成功巢穴中出飞的幼鸟数量减少。使用特定景观的繁殖力以及根据带环雄性艾草雀和布鲁尔麻雀的回捕率估算的成年存活率构建的简单种群增长模型表明，华盛顿州碎片化的灌丛草原可能正在成为一些物种的种群汇。当前的保护需求包括停止灌丛草原的进一步碎片化，尽可能将低产农田和一年生草地恢复为灌丛草原，并让公众认识到这些濒危生态系统的内在价值。
