Sexual segregation in foraging occurs in some species and populations of boobies (Sulidae), but it is not a general pattern. Sexual segregation in foraging may occur to avoid competition for food, and this competition may intensify during specific stages of breeding. We examined sexual segregation in foraging in relation to breeding stage in masked boobies Sula dactylatra at Rapa Nui by tracking simultaneously incubating and chick-rearing birds using GPS recorders (n = 18) and collected a total of 11 regurgitate samples. Stable isotope analyses (δ13C and δ15N) of whole blood samples were carried out in 20 birds. There were no differences in foraging trip parameters or diet between females and males. Both sexes traveled farther and for longer while incubating than while rearing chicks. Isotopic niches (δ13C and δ15N) overlapped to some degree among all groups at all times, but the lowest overlap between sexes occurred during incubation. While preying on ephemerally distributed flying fish, vertical or horizontal competition avoidance may be almost impossible, and thus females and males share their foraging grounds. Since birds were tracked simultaneously, shorter foraging trips of chick-rearing birds must be an effect of the constraints of provisioning the chick. Differences observed in δ15N and δ13C values between sexes may be caused by subtle differences in their foraging behaviors, or by differences in physiology linked to breeding. Our findings suggest that local oceanography and its inherent food distribution are determinants for sexual segregation in foraging patterns in masked boobies and possibly also other booby species. In some animals, females and males forage on different areas or prey on different species to avoid competition for food resources. In boobies (Sula sp.), some studies show evidence of sexual segregation in foraging and others do not. Here, we tested if sexual segregation in foraging occurred in masked boobies on the Pacific island of Rapa Nui by studying simultaneously incubating and chick-rearing birds. We found no evidence of sexual segregation on foraging behavior or diet. We discuss that the difference between this and other studies in boobies may be an effect of the local prey availability. When the prey community is more diverse and heterogeneously distributed, each sex may access different resources and thus sexual foraging segregation will occur. In contrast, in areas like Rapa Nui where prey resources are distributed ephemerally, sexual segregation in foraging will not be useful and is thus less likely to occur.

中文翻译：

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育种阶段，而不是性别，影响拉帕努伊蒙面鲣鸟的觅食特征

觅食中的性别隔离发生在鲣鸟（鲣科）的某些物种和种群中，但这不是普遍模式。为了避免食物竞争，可能会在觅食中进行性别隔离，而这种竞争可能会在繁殖的特定阶段加剧。我们通过使用 GPS 记录器（n = 18）同时跟踪孵化和小鸡饲养的鸟类，检查了与 Rapa Nui 的蒙面鲣鸟 Sula dactylatra 的繁殖阶段有关的觅食中的性别隔离，并收集了总共 11 个反刍样本。对 20 只鸡的全血样品进行了稳定同位素分析（δ13C 和 δ15N）。雌性和雄性在觅食旅行参数或饮食方面没有差异。两性在孵化时比在饲养小鸡时走得更远，时间更长。同位素生态位（δ13C 和 δ15N）在所有组中始终存在一定程度的重叠，但性别之间的最低重叠发生在孵化期间。在捕食短暂分布的飞鱼时，避免垂直或水平竞争几乎是不可能的，因此雌性和雄性共享它们的觅食地。由于鸟类是同时被跟踪的，因此饲养小鸡的鸟类较短的觅食行程一定是小鸡供应限制的影响。在两性之间观察到的 δ15N 和 δ13C 值的差异可能是由它们觅食行为的细微差异或与繁殖相关的生理差异引起的。我们的研究结果表明，当地海洋学及其固有的食物分布是蒙面鲣鸟和其他鲣鸟觅食模式性别隔离的决定因素。在一些动物中，雌性和雄性在不同的区域觅食或捕食不同的物种，以避免争夺食物资源。在鲣鸟 (Sula sp.) 中，一些研究显示了觅食过程中存在性别隔离的证据，而其他研究则没有。在这里，我们通过同时研究孵化和饲养小鸡的鸟类，测试了太平洋拉帕努伊岛上的蒙面鲣鸟在觅食方面是否存在性别隔离。我们没有发现觅食行为或饮食存在性别隔离的证据。我们讨论了这项研究与其他鲣鸟研究之间的差异可能是当地猎物可用性的影响。当猎物群落更加多样化和异质性分布时，每个性别可能获得不同的资源，因此会出现有性觅食隔离。相比之下，在像拉帕努伊这样的猎物资源短暂分布的地区，觅食中的性别隔离没有用，因此不太可能发生。