1. The eastern grey squirrel (hereafter ‘grey squirrel’) is considered one of the most damaging invasive alien species in Europe, with negative effects on native ecosystems. Despite it being widely perceived as a significant predator of bird eggs and chicks and as a competitor for nest sites, evaluation of the grey squirrel’s impact on European bird populations has been hindered by limited empirical data.
2. The aim was to review the incidence of grey squirrels as nest predators of and nest‐site competitors with European birds, and to use this information to identify species at potential risk of negative effects from within the grey squirrel’s expanding range in continental Europe.
3. A comprehensive literature review was conducted, and the data were used alongside additional new data, to assess nest predation and competition by grey squirrels in their current European range. Bird species were grouped by nest‐site type, which was used to predict the impact on similar species groups in regions of continental Europe predicted to be colonised by grey squirrels in the current century.
4. Camera‐monitoring and field evidence for 12 bird species and 12420 nests in Britain showed that grey squirrels rarely depredated eggs or chicks, affecting just 0.5% of nests. Nest‐site competition was also minor, with grey squirrels occupying 0.8% of 122 small tree cavities and 14% of 57 larger cavities. At least 69 bird species in continental Europe could be exposed to potential nest predation or competition from expanding grey squirrel populations within the current century, but population‐level effects currently appear to be unlikely.
5. Current evidence shows that grey squirrels are unlikely to be significant predators of or competitors with nesting birds in their present or projected range in Europe. However, further studies of more species in different regions would be valuable, particularly in urban and suburban habitats.

中文翻译：

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入侵东部东部灰松鼠Scuulus carolinensis的捕食和筑巢竞争对欧洲鸟类的当前和未来影响

1. 东部灰松鼠（以下简称“灰松鼠”）被认为是欧洲最具破坏性的外来入侵物种之一，对本土生态系统具有负面影响。尽管人们普遍认为灰松鼠是鸟卵和雏鸟的重要捕食者，并且是巢穴的竞争者，但是有限的经验数据阻碍了对灰松鼠对欧洲鸟类种群影响的评估。
2. 目的是审查灰松鼠作为欧洲鸟类的巢穴掠食者和巢穴竞争者的发生率，并利用此信息从灰松鼠在欧洲大陆范围扩大的范围内识别有潜在负面影响的物种。
3. 进行了全面的文献综述，并将这些数据与其他新数据一起使用，以评估灰松鼠在当前欧洲范围内的巢捕食和竞争。鸟类按巢位类型分组，这被用来预测对欧洲大陆地区类似物种组的影响，该地区在本世纪预计将被灰松鼠定居。
4. 在英国，有12种鸟类和12420个鸟巢的摄像机监控和现场证据显示，灰松鼠很少淘汰卵或小鸡，仅影响0.5％的鸟巢。巢地竞争也很小，灰松鼠占据了122个小树洞的0.8％，占57个大树洞的14％。在本世纪内，欧洲大陆上至少有69种鸟类可能会遭受潜在的巢捕食或竞争，这与灰松鼠种群的增长有关，但目前看来对种群的影响不大。
5. 当前的证据表明，灰松鼠不太可能成为欧洲目前或预计范围内筑巢鸟类的重要捕食者或竞争者。但是，对不同地区更多物种的进一步研究将是有价值的，尤其是在城市和郊区的栖息地中。