Riparian restoration in the southwestern United States frequently involves planting cottonwood (Populus spp.) and willow (Salix spp.). In the absence of flooding and gap‐forming disturbance, planted forests often senesce without further young tree recruitment. This has largely been the case in California riparian systems that historically supported state‐endangered western Yellow‐billed Cuckoo (Coccyzus americanus; Cuckoo). A decline in Cuckoo population numbers in the past 30 years has been associated with forest maturation. Other riparian species of concern show a concomitant decline, indicating the problem is not specific to Cuckoos. Although varying hypotheses exist for recent decline, alternative management practices have not been sufficiently explored to rule out breeding ground habitat quality as a major contributing factor. Few intensive Cuckoo datasets exist to test hypotheses about breeding habitat quality due to extremely low populations in the remaining occupied sites. We used a historical (1986–1996) spot mapping dataset from the South Fork Kern River Valley, CA to identify vegetation characteristics related to Cuckoo and five other sensitive riparian bird territory densities. We found Cuckoo densities were positively associated with increased vertical vegetative structure 1–5 m above ground with a threshold for mean tree height. Sensitive species densities were also related to vertical structure and started to decline with stand height greater than 6–8 m. Naturally regenerated sites had higher densities of most sensitive bird species than planted sites. We provide ideas for restoring mature forest with little vertical structure.

中文翻译：

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挑战我们对西部黄嘴杜鹃栖息地需求和公认的管理实践的理解

在美国西南部的河岸恢复经常涉及种植杨木（杨属）和柳树（柳属）。在没有洪水和形成缝隙的干扰的情况下，人工林常常会感觉衰弱，而没有再招募幼树。在很大程度上，加利福尼亚河岸系统就是这种情况，该系统历史上曾支持受国家威胁的西部黄嘴杜鹃（Coccyzus americanus; 布谷鸟）。在过去的30年中，布谷鸟数量的下降与森林的成熟有关。其他令人关注的河岸物种也随之减少，这表明该问题并非杜鹃所特有。尽管存在关于近期下降的各种假设，但尚未充分探索替代管理方法来排除繁殖地栖息地质量是主要的影响因素。很少有密集的布谷鸟数据集可以测试有关繁殖栖息地质量的假设，原因是剩余居住区中的种群极少。我们使用了加利福尼亚南叉克恩河谷的历史（1986–1996）点测绘数据集，以识别与杜鹃和其他五种敏感河岸鸟类领土密度有关的植被特征。我们发现杜鹃的密度与地面以上1–5 m的垂直植物生长结构呈正相关，且树的平均高度为阈值。敏感物种的密度也与垂直结构有关，并且随着林分高度大于6-8 m而开始下降。天然更新的地点比种植地点具有更高的敏感度最高的鸟类物种密度。我们提供了恢复垂直结构少的成熟林的想法。