Predation on smolts by Caspian terns (Hydroprogne caspia) has been identified as a factor limiting the restoration of some populations of anadromous salmonids (Oncorhynchus spp.) from the Columbia River basin that are listed under the U.S. Endangered Species Act. Implementation of a management plan to reduce numbers of Caspian terns nesting at the 2 largest colonies in the Columbia Plateau region of Oregon and Washington, USA, began in 2014 and is ongoing. We investigated the response of Caspian terns during 2014–2016 to reductions in nesting habitat at these 2 colonies. Management prevented terns from nesting at both colonies, and the estimated numbers of nesting pairs in the region declined significantly from a mean of 877 pairs during premanagement to 769 and 675 pairs in 2015 and 2016, respectively. The management objective of reducing numbers of nesting terns in the Columbia Plateau region to ≤200 breeding pairs was not achieved during the first 2 years of full implementation of the plan. Regional nesting success did not decline significantly following the initiation of management, and remained at levels considered sufficient to sustain the regional subpopulation. Despite the species’ capacity for long‐distance breeding dispersal, the majority of displaced terns exhibited stronger than expected philopatry to the Columbia Plateau region. Analysis of resightings of banded terns indicated that most (>80%) terns that nested in the Columbia Plateau region premanagement returned to the region in 2015 and 2016, but the proportion that returned as breeders decreased while the proportion that returned as nonbreeding floaters increased compared with premanagement. The proportion of banded terns that were unobserved also increased during management years, suggesting that more terns became floaters in the Pacific Flyway and went unobserved because they were prospecting and foraging in locations or regions where there was little or no monitoring. The unexpectedly high regional philopatry exhibited by terns during management was likely a reflection of the low availability of suitable alternative nesting habitat outside the region. Most terns that remained in the region displayed considerable flexibility in nest site selection by nesting either at a previously smaller, intermittently successful breeding colony or at a small new colony where nesting activity had not previously been recorded. As long‐lived seabirds, Caspian terns may integrate information regarding nesting success over several years before choosing to change nesting locations, longer than the 2 years of this study, especially if alternate locations are distant or intermittently available, or a history of nesting at multiple locations exists within the region. © 2020 The Wildlife Society.

中文翻译：

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里海燕鸥对筑巢栖息地管理性减少的反应

里海Hydro（Hydroprogne caspia）对软体动物的捕食被认为是限制某些淡水鲑鱼（Oncorhynchus）恢复的一个因素。spp。）来自《美国濒危物种法》所列的哥伦比亚河流域。2014年开始实施一项管理计划，以减少在俄勒冈州哥伦比亚高原地区和美国华盛顿的两个最大殖民地筑巢的里海燕鸥数量。我们调查了2014-2016年里海燕鸥对这两个殖民地筑巢栖息地减少的反应。管理层阻止燕鸥在两个殖民地筑巢，该区域的筑巢对估计数从预管理期间的平均877对下降到2015年和2016年的769对和675对。在全面实施该计划的前两年，没有实现将哥伦比亚高原地区的燕鸥数量减少到200对以下的管理目标。在开始管理后，区域筑巢成功并没有显着下降，而是保持在足以维持区域亚种群的水平。尽管该物种具有远距离繁殖传播的能力，但大多数流离失所的燕鸥在哥伦比亚高原地区仍表现出比预期更强的隐喻。对带状燕鸥的视域分析表明，在2015年和2016年，大多数栖息在哥伦比亚高原地区管理的燕鸥（> 80％）返回了该区域，但与繁殖者相比，返回的比例有所下降，而繁殖者的返回比例则有所增加进行预管理。在管理年期间，未被观察到的带状燕鸥的比例也有所增加，这表明，更多的燕鸥在太平洋航线上成为漂浮物，并没有被观察到，因为他们正在很少或根本没有监测的地点或地区进行觅食和觅食。燕鸥在管理过程中表现出的出乎意料的高区域哲学性很可能反映了该区域以外合适的替代性栖息地的可用性低。留在该区域的大多数燕鸥通过在先前较小的，间歇性成功的繁殖地或以前没有记录过筑巢活动的新的小地筑巢，在选择巢穴时表现出很大的灵活性。作为长寿海鸟，里海燕鸥可能会在选择改变筑巢地点之前的几年中整合有关筑巢成功的信息，这一时间要长于本研究的两年时间，尤其是在距离遥远或断断续续的位置，或者区域内存在多个位置嵌套的历史记录时。©2020野生动物协会。