Eastern European countries are considered a stronghold for the continent's farmland biodiversity. The abundance of farmland birds is one important element of this biodiversity. At the end of the 20th century, member states of the European Union (EU) experienced serious population declines of farmland birds due to agricultural intensification, which was not observed in the Eastern European nonmember states. In 2004, 10 mostly Eastern European countries acceded to the EU. It is thus important to ask whether this historical step resulted in changes of agricultural production and, in turn, in farmland bird populations. Here we used annual crop yields and monitoring data on farmland bird abundance in an Eastern European new EU‐member state and showed that agricultural production intensified and farmland bird populations declined steeply after country's EU accession. These results indicate that entering EU's Common Agricultural Policy caused significant deterioration of farmland biodiversity in a once biodiversity‐rich region.

中文翻译：

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加入欧盟后东欧国家农田鸟类的数量减少

东欧国家被认为是该大陆农田生物多样性的据点。农田鸟类的丰富是这一生物多样性的重要组成部分。20世纪末，由于农业集约化，欧洲联盟（EU）的成员国经历了农田鸟类的严重种群减少，东欧非成员国中没有发现这一现象。2004年，有10个主要是东欧国家加入了欧盟。因此，重要的是要问这个历史步骤是否导致了农业生产的变化，进而导致了农田鸟类的数量的变化。在这里，我们使用了东欧新欧盟成员国的年度农作物产量和农田鸟类丰度的监测数据，结果表明，该国加入欧盟后，农业生产集约化，农田鸟类的数量急剧下降。这些结果表明，加入欧盟的共同农业政策在曾经是生物多样性丰富的地区造成了农田生物多样性的严重恶化。