Common Tern (Sterna hirundo) breeding populations in inland North America have declined significantly since the 1970s. A 2012 survey of the large Manitoba lakes, previously the largest known inland population stronghold, reported a 57–67% decline in 20 years. A further 38% decline by 2017 highlights the urgent need for research and management. We use ground-based estimates of productivity and analysis of microsatellite markers to provide the first detailed insight into breeding status and movements of Common Terns in this region. At six breeding colonies in 2012, we recorded breeding success in fenced plots, counted fledglings, documented predators and floods, and collected blood samples for microsatellite analysis of movement. Productivity ranged from 0.0 to 2.0 chicks fledged per nest, being highest at large colonies (> 1000 nests) located far away from human settlements (20–30 km). Large-scale breeding failure from predation occurred at smaller colonies close to human settlement. The most common predators were Black-crowned Night Herons (Nycticorax nycticorax) and Great Horned Owls (Bubo virginianus), but we also report three novel predators: Bald Eagles (Haliaeetus leucocephalus), gray wolves (Canis lupus), and river otters (Lontra canadensis). Microsatellite analysis suggested little eastward emigration, but instead a 100-fold increase in immigration from the Great Lakes between the 1990s and 2010s. Substantial population declines in the Manitoba Lakes despite this influx imply that net losses are occurring within inland-breeding populations. Terns now appear to switch frequently between breeding colonies in the region, possibly in response to predation and/or flooding. Although some colonies achieved productivity during the one-year study, continued population decline indicates that monitoring and studies of adult survival and movement are needed, especially given the on-going environmental changes within the region. Only by coupling these data with further efforts in unsurveyed boreal regions can the status of inland-breeding Common Terns be determined and strategies developed to curb apparent, large-scale population declines.

中文翻译：

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了解北美内陆普通燕鸥的普遍下降：生产力估计、繁殖失败的原因以及普通燕鸥在曼尼托巴大湖中繁殖的运动

自 1970 年代以来，北美内陆的普通燕鸥 (Sterna hirundo) 繁殖种群已显着下降。2012 年对马尼托巴大湖进行的一项调查报告称，该湖曾是已知最大的内陆人口据点，在 20 年内下降了 57-67%。到 2017 年将进一步下降 38%，这凸显了对研究和管理的迫切需求。我们使用基于地面的生产力估计和微卫星标记分析，首次详细了解该地区普通燕鸥的繁殖状况和活动。在 2012 年的六个繁殖地，我们记录了围栏地块的繁殖成功，计算了雏鸟数量，记录了掠食者和洪水，并收集了血液样本以进行微卫星运动分析。生产力范围从每窝 0.0 到 2.0 只雏鸡，在大型群落中最高（> 1000 个巢穴）位于远离人类住区（20-30 公里）的地方。捕食导致的大规模繁殖失败发生在靠近人类住区的较小殖民地。最常见的食肉动物是黑冠夜鹭 (Nycticorax nycticorax) 和大角猫头鹰 (Bubo virginianus)，但我们还报告了三种新的食肉动物：白头鹰 (Haliaeetus leucocephalus)、灰狼 (Canis lupus) 和水獭 (Lontra)加拿大）。微卫星分析表明几乎没有向东移民，而是在 1990 年代至 2010 年代期间，来自五大湖的移民增加了 100 倍。尽管有大量涌入，但马尼托巴湖的种群数量大幅下降，这意味着内陆繁殖种群正在发生净损失。燕鸥现在似乎在该地区的繁殖地之间频繁切换，可能是为了应对捕食和/或洪水。尽管一些殖民地在为期一年的研究中实现了生产力，但人口持续下降表明需要对成年人的生存和活动进行监测和研究，特别是考虑到该地区正在进行的环境变化。只有将这些数据与未经调查的北方地区的进一步努力相结合，才能确定内陆繁殖的普通燕鸥的状况，并制定策略来遏制明显的大规模人口下降。