The Nature Conservancy, 1917 First Avenue, Seattle, Washington 98101, USA.
Ecol Appl. 2011 Mar;21(2):547-54. doi: 10.1890/10-0032.1.
Riparian habitats in the western United States support high avian abundance and diversity and are important areas for livestock grazing, although grazing contributes to the degradation of riparian vegetation. Complete removal of livestock is generally the most beneficial for bird communities, but alternative management approaches allowing for seasonal livestock grazing may also increase avian habitat quality. Determining management approaches that integrate conservation priorities and human use has the potential to improve conditions for birds across many grazed landscapes. We anticipated that both the full and seasonal exclusion of cattle from riparian areas would result in the recovery of avian populations. To test this, we experimentally compared the effects of total cattle exclusion vs. seasonal usage on bird populations in the riparian areas of two creeks in the San Joaquin Valley, California, USA. Avian species richness and average abundance were measured over six years, from 2001 to 2006. In general, native avian abundance and richness increased in both full- and seasonal-exclosure areas, with increases compared to the pretreatment year for all years except 2005. Habitats that had complete cattle exclusion recovered more significantly, with 29% lower avian abundance in seasonally grazed habitats. There was no significant difference in avian richness between the two grazing treatments, although richness did increase over time. In addition to increases in native species, abundance of nonnative birds and brood parasites also increased significantly, with a greater avian abundance in the full-exclusion areas. A direct comparison with the Breeding Bird Survey (BBS), to further investigate annual avian population trends, explained the native species decline in 2005. This comparison revealed that observed trends were the effect of experimental treatment rather than a reflection of regional trends. Although the overall trends indicate that the full exclusion of livestock from riparian areas results in more abundant bird populations, seasonal exclusion is also a successful method for avian recovery. Land managers should consider both options in riparian areas, selecting full cattle removal for avian management only and seasonal cattle removal for situations where incorporating conservation and land use practices is advantageous.
美国西部的河岸栖息地支持着丰富多样的鸟类，是牲畜放牧的重要区域，但放牧会导致河岸植被退化。完全禁止牲畜进入通常对鸟类群落最有益，但允许季节性放牧的替代管理方法也可能提高鸟类栖息地质量。确定整合保护重点和人类利用的管理方法有可能改善许多放牧景观中鸟类的状况。我们预计，完全禁止和季节性禁止牛群进入河岸区都将导致鸟类种群的恢复。为了验证这一点，我们在加利福尼亚州圣华金谷的两条溪流的河岸区，实验比较了完全禁止牛群进入和季节性使用对鸟类种群的影响。2001 年至 2006 年，我们用六年时间测量了鸟类物种丰富度和平均丰度。一般来说，在完全和季节性封闭区域，本地鸟类的丰度和丰富度都有所增加，除 2005 年以外，所有年份的增加都与预处理年份相比。完全禁止牛群进入的栖息地恢复得更为显著，季节性放牧栖息地的鸟类丰度降低了 29%。两种放牧处理方式之间在鸟类丰富度上没有显著差异，尽管丰富度随时间而增加。除了本地物种的增加外，非本地鸟类和雏鸟寄生虫的数量也显著增加，完全禁止放牧的区域鸟类数量更多。与鸟类繁殖调查（BBS）的直接比较，进一步研究了年度鸟类种群趋势，解释了 2005 年本地物种数量的下降。这种比较表明，观察到的趋势是实验处理的结果，而不是反映区域趋势。尽管总体趋势表明，将牲畜完全从河岸区排除会导致鸟类种群更丰富，但季节性排除也是鸟类恢复的成功方法。土地管理者应在河岸区考虑这两种选择，仅在鸟类管理方面选择完全禁止放牧，在有利于纳入保护和土地利用实践的情况下选择季节性禁止放牧。
