Context Insectivorous birds are sensitive to forest disturbances that may limit the availability of food consisting mainly of invertebrates. However, birds and invertebrates may be differently affected by forest disturbances while invertebrates may interact with disturbances. Objectives We aim to determine: (i) the effects of forest degradation on invertebrates and insectivorous birds; (ii) the effect of the availability of invertebrates as a food source on birds; (iii) interactions between food availability and forest degradation. Methods We selected 34 1-km radius landscape units, where the abundance of birds and invertebrates was sampled in the canopy and understory. Bird density as well as the abundance and richness of invertebrates were considered as dependent variables and analysed using Generalized Linear Mixed Model and Structural Equation Models. Remote-sensing indices of forest degradation were included as predictors. Results Eight indices of forest degradation affected canopy and understory invertebrates differently. Unlike invertebrates, bird abundance was affected by a smaller number of degradation indices, forest amounts as well as the cover of understory and canopy. Only two forest degradation indices had a comparable effect on bird abundance and invertebrates. We found causal relationships between understory invertebrates and the abundance of understory birds (all species and the small-sized ones), but also invertebrate abundance × forest cover interactions affected the abundance of a bird species. Conclusions Our results indicate that birds and invertebrates respond differently to forest degradation, but also provide evidence for bottom-up control by forest degradation and suggest food limitation varies with forest amounts.

中文翻译：

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森林退化对南方温带森林食虫鸟类和无脊椎动物的景观尺度影响

背景 食虫鸟类对森林干扰很敏感，这可能会限制主要由无脊椎动物组成的食物的供应。然而，鸟类和无脊椎动物可能会受到森林干扰的不同影响，而无脊椎动物可能会与干扰相互作用。目标 我们旨在确定： (i) 森林退化对无脊椎动物和食虫鸟类的影响；(ii) 无脊椎动物作为食物来源对鸟类的影响；(iii) 粮食供应与森林退化之间的相互作用。方法 我们选择了 34 个半径为 1 公里的景观单元，其中在冠层和林下对鸟类和无脊椎动物的丰度进行了采样。鸟类密度以及无脊椎动物的丰度和丰富度被视为因变量，并使用广义线性混合模型和结构方程模型进行分析。森林退化的遥感指数被列为预测指标。结果 8 个森林退化指标对冠层和林下无脊椎动物的影响不同。与无脊椎动物不同，鸟类丰度受到较少数量的退化指数、森林数量以及林下和树冠覆盖率的影响。只有两个森林退化指数对鸟类数量和无脊椎动物有相当的影响。我们发现林下无脊椎动物与林下鸟类（所有物种和小型鸟类）的数量之间存在因果关系，但无脊椎动物丰度×森林覆盖相互作用也影响了鸟类物种的丰度。结论我们的结果表明鸟类和无脊椎动物对森林退化的反应不同，但也为森林退化自下而上控制提供了证据，并表明食物限制随森林数量而变化。