BACKGROUND In recent decades, a decrease of passerine densities was documented in Mediterranean shrublands. At the same time, a widespread encroachment of Aleppo pines (Pinus halepensis) to Mediterranean shrubland occurred. Such changes in vegetation structure may affect passerine predator assemblage and densities, and in turn impact passerine densities. Depredation during the nesting season is an important factor to influence passerine population size. Understanding the effects of changes in vegetation structure (pine encroachment) on passerine nesting success is the main objective of this study. We do so by assessing the effects of Aleppo pine encroachment on Sardinian warbler (Sylvia melanocephala) nest depredation in Mediterranean shrublands. We examined direct and indirect predation pressures through a gradients of pine density, using four methods: (1) placing dummy nests; (2) acoustic monitoring of mobbing events; (3) direct observations on nest predation using cameras; and (4) observation of Eurasian jay (Garrulus glandarius) behaviour as indirect evidence of predation risk. RESULTS We found that Aleppo pine encroachment to Mediterranean shrublands increased nest predation by Eurasian jays. Nest predation was highest in mixed shrubland and pines. These areas are suitable for warblers but had high occurrence rate of Eurasian jays. CONCLUSIONS Encroaching pines directly increase activity of Eurasian jays in shrubland habitats, which reduced the nesting success of Sardinian warblers. These findings are supported by multiple methodologies, illustrating different predation pressures along a gradient of pine densities in natural shrublands. Management of Aleppo pine seedlings and removal of unwanted trees in natural shrubland might mitigate arrival and expansion of predators and decrease the predation pressure on passerine nests.

中文翻译：

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由于地中海灌木丛中的阿勒颇松（Pinus halepensis）受到侵害，鸣禽巢的掠夺性增加。

背景技术在最近的几十年中，地中海灌木丛中的雀形目密度降低了。同时，发生了阿勒颇松（Pinus halepensis）对地中海灌丛的广泛侵袭。植被结构的这种变化可能会影响雀形目捕食者的组装和密度，进而影响雀形目的密度。筑巢季节的掠夺是影响雀形目种群规模的重要因素。了解植被结构变化（松木侵占）对雀形目成功筑巢的影响是本研究的主要目的。我们通过评估阿勒颇松的入侵对地中海灌丛中撒丁岛莺（Sylvia melanocephala）巢的掠夺的影响来实现这一目标。我们通过松密度的梯度检查了直接和间接的捕食压力，使用四种方法：（1）放置虚拟嵌套；（2）对围捕事件进行声波监测；（3）利用摄像头直接观察巢内捕食行为；（4）观察到欧亚黑鸦（Garrulus glandarius）行为是掠食风险的间接证据。结果我们发现，阿勒颇松对地中海灌丛的侵占增加了欧亚j鸟对巢的捕食。混合灌木丛和松树中的巢穴捕食率最高。这些地区适合鸣鸟，但欧亚ura鸟的发生率很高。结论侵蚀性松树直接增加了灌木丛生境中欧亚j鸟的活动，这降低了撒丁岛莺的筑巢成功率。这些发现得到了多种方法的支持，这些方法说明了天然灌木林中沿松密度梯度的不同捕食压力。