Background Non-native species are often introduced in cities, where they take advantage of microclimatic conditions, resources provided by humans, and competitor/predator release to establish and proliferate. However, native communities in the surrounding rural or natural areas usually halt their spread through biotic resistance, mainly via top-down regulative processes (predation pressure). Here, we show an unusual commensal interaction between exotic and native bird species that favours the spread of the former from urban to rural habitats. Results We show how Monk parakeets Myiopsitta monachus, an invasive species often introduced in cities worldwide, associated for breeding with a much larger, native species (the white stork Ciconia ciconia) to reduce predation risk in central Spain, thus allowing their colonization of rural areas. Parakeets selected stork nests close to conspecifics and where breeding raptors were less abundant. Parakeets always flushed when raptors approached their nests when breeding alone, but stayed at their nests when breeding in association with storks. Moreover, when storks abandoned a nest, parakeets abandoned it in the following year, suggesting that storks actually confer protection against predators. Conclusions Our results show how a protective-nesting association between invasive and native species can counteract biotic resistance to allow the spread of an invasive species across non-urban habitats, where they may become crop pests. Monk parakeet populations are now growing exponentially in several cities in several Mediterranean countries, where they coexist with white storks. Therefore, management plans should consider this risk of spread into rural areas and favour native predators as potential biological controllers.

中文翻译：

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与本地物种的保护性筑巢协会抵消了入侵长尾小鹦鹉从城市栖息地传播到农村栖息地的生物抗性。

背景 外来物种经常被引入城市，它们利用小气候条件、人类提供的资源以及竞争者/捕食者的释放来建立和繁殖。然而，周围农村或自然地区的土著社区通常通过生物抗性来阻止它们的传播，主要是通过自上而下的调节过程（捕食压力）。在这里，我们展示了外来鸟类和本地鸟类之间不寻常的共生相互作用，这有利于前者从城市栖息地传播到农村栖息地。结果 我们展示了僧侣长尾小鹦鹉 Myiopsitta monachus（一种经常在世界各地的城市引入的入侵物种）如何与更大的本地物种（白鹳 Ciconia ciconia）繁殖以降低西班牙中部的捕食风险，从而使其在农村地区定居. 长尾小鹦鹉选择靠近同类的鹳巢，而繁殖猛禽数量较少的地方。当猛禽单独繁殖时，长尾小鹦鹉总是在猛禽接近它们的巢穴时脸红，但当与鹳一起繁殖时，它会留在它们的巢穴中。此外，当鹳鸟放弃巢穴时，长尾小鹦鹉也会在次年放弃它，这表明鹳鸟实际上可以保护自己免受捕食者的侵害。结论 我们的结果显示了入侵物种和本地物种之间的保护性筑巢关联如何抵消生物抗性，从而使入侵物种在非城市栖息地传播，在那里它们可能成为作物害虫。和尚长尾小鹦鹉种群现在在几个地中海国家的几个城市呈指数级增长，在那里它们与白鹳共存。所以，