Division of Biology, Kansas State University, Manhattan, KS 66506-4901, USA.
Oecologia. 2010 Mar;162(3):803-13. doi: 10.1007/s00442-009-1549-9. Epub 2010 Jan 6.
Extremes in rangeland management, varying from too-frequent fire and intensive grazing to the suppression of both, threaten rangeland ecosystems worldwide. Intensive fire and grazing denude and homogenize vegetation whereas their suppression increases woody cover. Although habitat loss is implicated in grassland bird declines, degradation through intensive management or neglect also decreases breeding habitat and may reduce nesting success through increased rates of nest predation. Snakes are important nest predators, but little is known about how habitat use in snakes relates to predation risk for grassland birds nesting within tallgrass prairie subjected to different grazing and fire frequencies. We evaluated nest survival in the context of habitat used by nesting songbirds and two bird-eating snakes, the eastern yellowbelly racer Coluber constrictor flaviventris and Great Plains ratsnake Pantherophis emoryi. Daily nest survival rates decreased with increasing shrub cover and decreasing vegetation height, which characterize grasslands that have been neglected or intensively managed, respectively. Discriminant function analysis revealed that snake habitats were characterized by higher shrub cover, whereas successful nests were more likely to occur in areas with tall grass and forbs but reduced shrub cover. Because snakes often use shrub habitat, birds nesting in areas with increased shrub cover may be at higher risk of nest predation by snakes in addition to other predators known to use shrub habitat (e.g., mid-sized carnivores and avian predators). Depredated nests also occurred outside the discriminant space of the snakes, indicating that other predators (e.g., ground squirrels Spermophilus spp. and bullsnakes Pituophis catenifer) may be important in areas with denuded cover. Targeted removal of shrubs may increase nest success by minimizing the activity of nest predators attracted to shrub cover.
极端的牧场管理方式，从过于频繁的火灾和密集放牧到两者的抑制，都威胁着全球的牧场生态系统。密集的火灾和放牧使植被裸露和同质化，而抑制它们则会增加木本植物的覆盖。尽管栖息地的丧失与草地鸟类的减少有关，但通过密集管理或忽视导致的退化也会减少繁殖栖息地，并可能通过增加巢捕食率来降低筑巢成功率。蛇是重要的巢捕食者，但对于在经历不同放牧和火灾频率的高草草原中筑巢的草地鸟类，蛇类对栖息地的利用与捕食风险之间的关系知之甚少。我们评估了巢的存活率，其背景是筑巢鸣禽和两种食鸟蛇类（东部黄腹游蛇 Coluber constrictor flaviventris 和大平原鼠蛇 Pantherophis emoryi）所利用的栖息地。每日巢存活率随着灌木覆盖度的增加和植被高度的降低而降低，这分别代表着被忽视或密集管理的草原的特征。判别函数分析表明，蛇类栖息地的灌木覆盖度较高，而成功的巢穴更有可能出现在高草和草本植物较多但灌木覆盖度较低的区域。由于蛇类通常利用灌木栖息地，因此在灌木覆盖度增加的区域筑巢的鸟类可能面临更高的巢捕食风险，除了已知利用灌木栖息地的其他捕食者（例如，中型食肉动物和鸟类捕食者）之外。被掠夺的巢穴也发生在蛇类判别空间之外，这表明在植被裸露的区域，其他捕食者（例如，地松鼠 Spermophilus spp. 和响尾蛇 Pituophis catenifer）可能很重要。有针对性地去除灌木可以通过减少吸引到灌木覆盖的巢捕食者的活动来提高巢的成功率。
