Abstract Among birds exhibiting conspecific brood parasitism (CBP), parasites demonstrate a variety of intriguing tactics for selecting a host nest, including preference for safe nests (i.e., avoiding nests depredated during the previous season). Brood parasites of birds that do not reuse nest sites, however, are limited to nest-site information available to them during the current breeding season. This study explores cues used by brood parasites in a population of red-breasted mergansers nesting in upland vegetation and sandy substrate that prohibits reuse of nest sites in consecutive years. Nest-site and host traits were measured for 33 parasitized and 23 non-parasitized nests. There was no association between CBP and nest-site traits potentially providing cues about nest safety from avian predators (concealment and density of nesting larids), likely due to very low rates of egg predation. Distance to shore for parasitized nests was slightly greater than for unparasitized nests. Parasites did not select nests in relation to host age, mass, date of nest initiation, or stage of nesting (laying or incubation). Artificial nests were used to simulate natural nests without a host and to assess whether host presence serves as a cue for parasites. The proportion of natural nests receiving ≥ 1 foreign egg (60% of 15 nests) was thrice that for artificial nests (21% of 14 nests). Some aspect of host presence may therefore be an important, but not necessary, cue for brood parasites targeting nests that are heavily concealed in uplands. Significance statement Whenever brood parasitism is a well-developed component of reproduction, selection is expected to favor brood parasites that make use of environmental or social information allowing them to discriminate among host nests and maximize reproductive success. We assessed cues used by brood parasites in ground-nesting red-breasted mergansers for which conspecific brood parasitism (CBP) is common, and nests are well concealed in upland vegetation. Observations at parasitized and unparasitized nests revealed that nest-site safety and visibility from habitat edges are not central to laying decisions by parasites in this population. Brood parasites, however, were considerably more likely to lay their eggs in natural nests with a host than in artificial nests without a host, suggesting that some aspect of host presence is important in the nest-site selection process for parasites. The ability of brood parasites to discriminate among nests based on host presence is expected to affect parasite success because individuals can avoid nests in which their eggs are doomed to fail (e.g., abandoned nests).

中文翻译：

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高地筑巢鸟的同种巢寄生：寄生虫用来选择巢穴的线索

摘要 在表现出同种繁殖寄生 (CBP) 的鸟类中，寄生虫表现出各种选择寄主巢穴的有趣策略，包括对安全巢穴的偏好（即，避免在上一季中被破坏的巢穴）。然而，不重复使用筑巢地点的鸟类的繁殖寄生虫仅限于它们在当前繁殖季节可获得的筑巢地点信息。这项研究探索了红胸秋沙鸭种群中的繁殖寄生虫使用的线索，这些线索在高地植被和沙质基质中筑巢，这些植物和沙质基质禁止连续几年重复使用筑巢地点。测量了 33 个寄生巢和 23 个非寄生巢的巢址和寄主性状。CBP 与巢址特征之间没有关联，可能会提供有关鸟类捕食者的巢穴安全性的线索（巢穴的隐蔽性和密度），可能是由于鸡蛋捕食率非常低。寄生巢穴到岸边的距离略大于未寄生巢穴。寄生虫不会根据宿主年龄、质量、筑巢日期或筑巢阶段（产卵或孵化）来选择巢穴。人工巢穴被用来模拟没有宿主的自然巢穴，并评估宿主的存在是否可以作为寄生虫的线索。接收 ≥ 1 个外来卵的天然巢（15 个巢的 60%）的比例是人工巢（14 个巢的 21%）的三倍。因此，寄主存在的某些方面可能是一个重要的，但不是必需的，对于以高度隐藏在高地的巢穴为目标的寄生虫来说，这是一个重要的线索。意义说明 当巢寄生是繁殖的一个发育良好的组成部分时，预计选择将有利于利用环境或社会信息的寄生虫，使它们能够区分寄主巢穴并最大限度地提高繁殖成功率。我们评估了在地面筑巢的红胸秋沙鸭中繁殖寄生虫使用的线索，这些秋沙鸭的同种繁殖寄生 (CBP) 很常见，并且巢很好地隐藏在高地植被中。对寄生和未寄生巢穴的观察表明，巢穴安全和栖息地边缘的能见度对于该种群中的寄生虫做出的决定并不重要。然而，与没有宿主的人工巢相比，有寄主的天然巢中产卵的可能性要大得多，这表明寄主存在的某些方面在寄生虫的巢址选择过程中很重要。