Conservation Biology Graduate Program, University of Minnesota, 1980 Folwell Avenue, St. Paul, MN 55108, USA.
Conserv Biol. 2011 Oct;25(5):983-92. doi: 10.1111/j.1523-1739.2011.01719.x. Epub 2011 Jul 28.
European earthworms (Lumbricus spp.) are spreading into previously earthworm-free forests in the United States and Canada and causing substantial changes, including homogenization of soil structure, removal of the litter layer, and reduction in arthropod abundance and species richness of understory plants. Whether these changes affect songbirds that nest and forage on the forest floor is unknown. In stands with and without earthworms in the Chequamegon-Nicolet National Forest, Wisconsin (U.S.A.), we surveyed for, monitored nests of, and measured attributes of habitat of Ovenbirds (Seiurus aurocapillus) and Hermit Thrushes (Catharus guttatus), both ground-dwelling songbirds, and we sampled earthworms at survey points and nests. Bird surveys indicated significantly lower densities of Ovenbirds and Hermit Thrushes in relation to Lumbricus invasions at survey point and stand extents (3.1 and 15-20 ha, respectively). Modeling of Ovenbird nest survival (i.e., the probability that nestlings successfully fledge) indicated that lower survival probabilities were associated with increased sedge cover and decreased litter depth, factors that are related to Lumbricus invasions, possibly due to reduced nest concealment or arthropod abundance. Our findings provide compelling evidence that earthworm invasions may be associated with local declines of forest songbird populations.
欧洲蚯蚓（Lumbricus spp.）正在扩散到美国和加拿大以前没有蚯蚓的森林中，并造成了重大变化，包括土壤结构的均匀化、凋落物层的去除以及节肢动物数量和林下植物物种丰富度的减少。这些变化是否会影响在森林地面筑巢和觅食的鸣禽尚不清楚。在威斯康星州（美国）的切卡梅戈-尼科莱特国家森林中，有无蚯蚓的林分中，我们调查了地面筑巢的鸣禽——烤箱鸟（Seiurus aurocapillus）和隐士夜鸫（Catharus guttatus）的鸟巢，并监测了其栖息地属性，还在调查点和鸟巢处采集了蚯蚓样本。鸟类调查表明，烤箱鸟和隐士夜鸫的密度与蚯蚓入侵的调查点和林分范围（分别为 3.1 和 15-20 公顷）显著相关。烤箱鸟巢存活率（即雏鸟成功出飞的概率）的模型表明，存活率较低与莎草覆盖度增加和凋落物深度减小有关，这些因素与蚯蚓入侵有关，可能是由于巢的隐蔽性降低或节肢动物数量减少。我们的研究结果提供了令人信服的证据，表明蚯蚓入侵可能与森林鸣禽种群的局部减少有关。
