Forest structure and composition in eastern U.S. forests are changing because of forest regeneration after farmland abandonment, less frequent occurrence of severe disturbances, and climate change. Some of these changes may disproportionally affect birds that rely on gap dynamics or other forest canopy disturbances to create understory habitat. The Canada Warbler (Cardellina canadensis) is one such understory specialist that has undergone consistent declines. We assessed environmental and interspecific factors associated with Canada Warbler space use in its southern breeding distribution to understand potential causes of population declines and inform conservation efforts. We evaluated Canada Warbler occupancy from 840 point count surveys conducted in 2017 and 2018 at 470 unique locations (79% of locations surveyed in both years) throughout Monongahela National Forest, West Virginia, USA. We modeled Canada Warbler occupancy probability as a function of environmental variables and included Black-throated Blue Warbler (Setophaga caerulescens) and Hermit Thrush (Catharus guttatus) as interacting species because all three species exhibit similar habitat preferences. Canada Warblers were most likely to occur in areas with rhododendron (Rhododendron maximum) density > 0.27 stems/m² and within 3 m of riparian areas (streams and wetlands). They were also more likely to occur in mid-elevation (highest occupancy at 930 m) northern hardwood forests when Black-throated Blue Warblers were also present. Black-throated Blue Warblers were most likely to occupy mid-elevation sites with high shrub density, whereas Hermit Thrushes were more likely to occupy high-elevation, old-age forests. Potential management actions could focus on conserving riparian areas in northern hardwood forests, especially those with dense rhododendron thickets. Such potential actions could also be beneficial across the entire elevation range we explored within the region (500–1300 m). Canada Warblers may be benefiting from the recent spread of rhododendron habitats and northern hardwood forest types within West Virginia.

中文翻译：

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林下结构和异种特性影响保护关注的地面筑巢物种的占有率，加拿大莺

美国东部森林的森林结构和组成正在发生变化，因为农田撂荒后的森林再生、严重干扰的发生频率降低以及气候变化。其中一些变化可能不成比例地影响依赖间隙动态或其他森林树冠干扰来创造林下栖息地的鸟类。加拿大莺（Cardellina canadensis）就是这样的林下专家之一，一直在下降。我们评估了与加拿大莺在其南部繁殖分布中的空间使用相关的环境和种间因素，以了解种群下降的潜在原因并为保护工作提供信息。我们通过 2017 年和 2018 年在美国西弗吉尼亚州莫农加赫拉国家森林的 470 个独特地点（两年调查地点的 79%）进行的 840 点计数调查评估了加拿大莺的入住率。我们将加拿大莺占用概率建模为环境变量的函数，并将黑喉蓝莺（Setophaga caerulescens）和隐士画眉（Catharus guttatus）作为相互作用的物种，因为这三个物种都表现出相似的栖息地偏好。加拿大莺最有可能出现在杜鹃花（杜鹃花最大）密度 > 0.27 茎/m² 和河岸地区（溪流和湿地）3 m 以内的地区。当黑喉蓝莺也存在时，它们也更有可能出现在海拔中部（最高占用率为 930 m）北部硬木林中。黑喉蓝莺最有可能占据高灌木密度的中海拔地点，而隐士画眉更可能占据高海拔的老年森林。潜在的管理行动可以集中在保护北部阔叶林的河岸地区，尤其是那些杜鹃花丛茂密的地区。这种潜在的行动也可能对我们在该区域内探索的整个海拔范围（500-1300 m）有益。加拿大莺可能会受益于最近在西弗吉尼亚州的杜鹃栖息地和北部硬木森林类型的蔓延。潜在的管理行动可以集中在保护北部阔叶林的河岸地区，尤其是那些杜鹃花丛茂密的地区。这种潜在的行动也可能对我们在该区域内探索的整个海拔范围（500-1300 m）有益。加拿大莺可能会受益于最近在西弗吉尼亚州的杜鹃栖息地和北部硬木森林类型的蔓延。潜在的管理行动可以集中在保护北部阔叶林的河岸地区，尤其是那些杜鹃花丛茂密的地区。这种潜在的行动也可能对我们在该区域内探索的整个海拔范围（500-1300 m）有益。加拿大莺可能会受益于最近在西弗吉尼亚州的杜鹃栖息地和北部硬木森林类型的蔓延。