Food availability sets the stage for incubation behaviour of a female bird and thereby indirectly determines the nest temperature, which in turn affects development and metabolism of avian embryos. Changes in development and metabolism in turn are known to influence offspring’s ability to adjust to environmental changes later in life. However, few studies have investigated the role of interspecific differences in incubation behaviour in relation to niche separation between competing sibling species. We studied the effects of habitat quality (in terms of caterpillar availability) on incubation behaviour of two ecologically similar and closely related species, collared and pied flycatchers (Ficedula albicollis and F. hypoleuca), in their hybrid zone on the island of Öland, Sweden. Even though both species prefer caterpillar-rich deciduous forests as nesting sites, collared flycatchers, whose nestlings have higher energetic demands, are able to nest only in deciduous forests, whereas pied flycatchers have more flexible habitat requirements. Overall, higher food availability was associated with increased nest attendance, higher incubation temperature and a lower number of foraging trips across species. In addition, collared flycatchers had more frequent and shorter foraging trips across habitat types, allocated more heat to eggs and therefore maintained higher nest temperatures compared to pied flycatchers. We argue that the higher heat allocation or the need to maintain a higher nest temperature for embryo development may constrain collared flycatchers to focus on relatively more profitable prey. Our results highlight the importance of considering incubation behaviour in the context of understanding species differences in niche use. Niche separation plays an important role in mitigating effects of competition between closely related species. Whether species differences in incubation behaviour relate to differences in niche use remains unknown. We compared incubation behaviour of two sympatric flycatcher species that differ in sensitivity to food availability. The competitively more dominant and larger species, the collared flycatcher, whose nestlings are more sensitive to food shortages, made more frequent foraging trips but allocated more heat to eggs, leading to higher nest temperature despite lower nest attendance, compared to pied flycatchers. These interspecific differences may be a result of differences in embryo sensitivity or female physiology and contribute to the niche separation between the species, which in turn can facilitate coexistence.

中文翻译：

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两种竞争捕蝇器物种的孵化行为和生态位分离的差异

食物可用性为雌鸟的孵化行为奠定了基础，从而间接决定了巢穴温度，进而影响鸟类胚胎的发育和新陈代谢。众所周知，发育和新陈代谢的变化会影响后代在以后的生活中适应环境变化的能力。然而，很少有研究调查种间差异在孵化行为中与竞争同胞物种之间生态位分离的作用。我们研究了栖息地质量（就毛毛虫可用性而言）对两种生态相似且密切相关的物种的孵化行为的影响，即有领和花斑捕蝇器（Ficedula albicollis 和 F. hypoleuca），它们位于瑞典厄兰岛的杂交区. 尽管这两个物种都喜欢毛毛虫丰富的落叶林作为筑巢地，但有项圈的捕蝇器，其雏鸟对能量的需求更高，只能在落叶林中筑巢，而花斑捕蝇器的栖息地要求更灵活。总体而言，较高的食物可用性与增加的巢穴出勤率、较高的孵化温度和较少的跨物种觅食次数有关。此外，带项圈的捕蝇器在栖息地类型之间的觅食行程更频繁且更短，为卵分配更多的热量，因此与带斑的捕蝇器相比，它们保持更高的巢穴温度。我们认为，较高的热量分配或需要为胚胎发育维持较高的巢穴温度可能会限制带项圈的捕蝇器专注于相对更有利可图的猎物。我们的结果强调了在了解生态位使用中物种差异的背景下考虑孵化行为的重要性。生态位分离在减轻密切相关物种之间竞争的影响方面起着重要作用。孵化行为的物种差异是否与生态位利用的差异有关仍然未知。我们比较了两种对食物供应敏感度不同的同域捕蝇器物种的孵化行为。与花斑捕蝇器相比，竞争更具优势和更大的物种，即有项圈的捕蝇器，其雏鸟对食物短缺更敏感，进行更频繁的觅食旅行，但将更多的热量分配给鸡蛋，导致巢穴温度更高，尽管巢穴出勤率较低。