Cryptic interactions among individuals in animal societies can be challenging to detect due to their rarity or their covert nature, but they can have important fitness consequences for the individuals involved. Using radiofrequency identification (RFID) technology, we examined the pattern and function of visits to the nests of conspecifics in western bluebirds, Sialia mexicana. Western bluebirds live in kin neighbourhoods year-round and exhibit a low frequency of cooperative breeding. Various functions have been proposed for extraterritorial visits, but few studies explore multiple potential functions. We asked whether extraterritorial visits in western bluebirds are consistent with (1) seeking extrapair copulations (EPCs), (2) prospecting for future nest sites or mates and/or (3) maintaining relationships with kin. We found some evidence supporting all three functions of visits. Postdawn visits made by males to unrelated females were significantly more likely to occur during the period in which males seek within-pair matings than outside this period. We found that visiting a given nestbox or a given potential mate was associated with an increased probability of nesting in that box or with the potential mate the subsequent year, suggesting that some visits are linked to prospecting. Finally, males preferentially visited kin: the proportion of visits to relatives was greater than the expected mean proportion of visits if males visited boxes randomly while travelling the same distance. Our work supports multiple functions of extraterritorial visits and highlights the importance of rare and cryptic behaviours to understanding social behaviour.

中文翻译：

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合作繁殖鸣禽的域外访问与多种功能一致

由于其稀有性或隐蔽性，动物社会中个体之间的隐秘互动可能难以检测，但它们可能对所涉及的个体产生重要的健康影响。我们使用射频识别 (RFID) 技术检查了访问西部蓝鸟 Sialia mexicana 同种鸟巢的模式和功能。西部蓝鸟常年生活在近亲社区，合作繁殖频率较低。已经提出了域外访问的各种功能，但很少有研究探索多种潜在功能。我们询问西部蓝鸟的域外访问是否与 (1) 寻求额外的交配 (EPC)、(2) 寻找未来的巢址或配偶和/或 (3) 保持与亲属的关系一致。我们发现了一些证据支持访问的所有三种功能。在雄性寻求成对交配的时期内，雄性对无关雌性的黎明后访问比在此时期之外发生的可能性要大得多。我们发现访问给定的巢箱或给定的潜在伴侣与在该巢箱中筑巢的可能性增加或随后一年与潜在伴侣筑巢的可能性有关，这表明某些访问与探矿有关。最后，男性优先访问亲属：如果男性在相同距离内随机访问盒子，则访问亲属的比例大于预期的平均访问比例。我们的工作支持域外访问的多种功能，并强调了罕见和神秘行为对理解社会行为的重要性。