Data from: Rodent-avoidance, topography and forest structure shape territory selection of a forest bird

Background - Understanding the factors underlying habitat selection is important in ecological and evolutionary contexts, and crucial for developing targeted conservation action in threatened species. However, the key factors associated to habitat selection often remain poorly known. We evaluated hypotheses related to abiotic and biotic factors thought to affect territory selection of the wood warbler Phylloscopus sibilatrix, a passerine living in an unpredictable environment owing to irregular rodent outbreaks and showing long-term declines particularly in Western Europe. Results - Comparing breeding territories to unoccupied areas located close-by revealed that territory occupancy in north-western Switzerland was positively related to slope steepness (topographic hypothesis supported) as well as to numbers of tussocks and trees, respectively, while it showed a unimodal relationship to cover of herb layer (forest structure hypothesis supported). Furthermore, a strong negative correlation between breeding territory occupancy and rodent numbers was found, suggesting that wood warblers avoid areas with high rodent densities (rodent-avoidance hypothesis supported). Comparing breeding territories to abandoned territories showed that breeding territories were located on steeper slopes (topography hypothesis supported), at larger distance from the forest edge (anthropogenic disturbance hypothesis supported) and harboured more trees (forest structure hypothesis supported) than abandoned territories. Conclusions - Aside from structural and topographic features of the habitat, wood warblers are affected by rodent numbers when settling, making habitat selection unpredictable from year to year. Forestry practices promoting relatively high tree densities, few bushes and an intermediate low-growing ground vegetation cover would enhance habitat quality for this declining passerine. In contrast, forestry practices aiming at increasing light in forests (selective thinning, group-felling) or keeping forest stands permanently covered with shrubs, bushes and trees of various sizes (continuous cover forestry) do not benefit the wood warbler.

研究背景：明晰生境选择的内在驱动因子，是生态学与进化生物学领域的核心议题之一，同时对濒危物种的针对性保护行动制定至关重要。然而，与生境选择相关的关键驱动因子往往仍未得到充分阐明。本研究针对非生物与生物因子相关假说展开评估，这些因子被认为会影响林柳莺（Phylloscopus sibilatrix）的领域选择。该雀形目鸟类的生存环境因啮齿动物周期性爆发而难以预测，其种群数量长期呈下降趋势，在西欧地区尤为显著。
研究结果：将繁殖领域与邻近的未占用区域进行对比后发现，瑞士西北部的林柳莺领域占有率与坡度、草丘数量以及树木数量均呈显著正相关，同时与草本层盖度呈单峰关系，该结果支持了地形假说与森林结构假说。此外，研究还发现繁殖领域占有率与啮齿动物种群数量存在显著负相关，表明林柳莺会避开啮齿动物密度较高的区域，该结果支持了啮齿动物避让假说。将繁殖领域与废弃领域进行对比后发现，繁殖领域相较于废弃领域，所处坡度更陡、距离林缘更远，且树木数量更多，这一结果分别支持了地形假说、人为干扰假说与森林结构假说。
研究结论：除生境的结构与地形特征外，林柳莺在繁殖定居过程中还会受到啮齿动物种群数量的影响，这使得其生境选择在不同年份间难以预测。对于这种种群数量持续下降的雀形目鸟类而言，采用维持较高树木密度、较少灌丛以及中等高度草本植被盖度的营林措施，可有效提升其生境质量。与之相反，旨在提升林内光照的营林措施（如择伐、团状采伐），或是采用永久保留不同大小灌木、灌丛与树木覆盖的连续覆盖森林经营模式，均无法为林柳莺带来益处。