Data from: Simulated moult reduces flight performance but overlap with breeding does not affect breeding success in a long-distance migrant

1. Long-distance migrants are time-constrained as they need to incorporate many annual cycle stages within a year. Migratory passerines moult in the short interval between breeding and migration. To widen this interval, moult may start while still breeding, but this results in flying with moulting wings when food provisioning. 2. We experimentally simulated wing gaps in breeding male pied flycatchers by plucking 2 primary feathers from both wings. We quantified the nest visitations of both parents, proportion of high-quality food brought to the nestlings and adults and nestlings condition. Differences in oxidative damage caused by a possible reduction in flight efficiency were measured in amounts of ROMs and OXY in the blood. We also measured how flight performance was affected with recordings of the male`s escape flight using high-speed cameras. Finally, we collected data on adult survival, clutch size and laying date in the following year. 3. “Plucked” males travelled a 5% shorter distance per wingbeat, showing that our treatment reduced flight performance. In line with this, “plucked” males visited their nests less often. Females of “plucked” males, however, visited the nest more often than controls, and fully compensated their partner’s reduced visitation rate. As a result, there were no differences between treatments in food quality brought to the nest, adult or chick mass or number of successfully fledged chicks. Males did not differ in their oxidative damage or local survival to the following year. In contrast, females paired with plucked males tended to return less often to breed in the next year in comparison to controls, but this difference was not significant. For the birds that did return there were no effects on breeding. 5. Our results reveal that wing gaps in male pied flycatchers reduce their flight performance, but when it occurs during breeding they prioritise their future reproduction by reducing parental care. As a result, there is no apparent detriment to their condition during breeding. Because non-moulting females are able to compensate their partner’s reduced care, there is also no immediate costs to the offspring, but females may pay the cost suffering from a reduced survival.

1. 长途迁徙鸟类受时间约束，需在一年内完成多个年度生活史阶段。迁徙鸣禽的换羽仅发生在繁殖与迁徙之间的短暂间隙内。为延长该间隙时长，部分个体可在繁殖期内便启动换羽程序，但这会导致其在育雏觅食时仍携带着正在换羽的翅膀飞行。
2. 本研究通过拔除繁殖期雄性斑姬鹟（pied flycatchers）两翼各2枚初级飞羽，实验模拟了其翅膀出现羽隙的状态。我们量化分析了双亲的巢内育雏到访频次、投喂雏鸟的优质食物占比，以及成鸟与雏鸟的身体状况。针对飞行效率下降可能引发的氧化损伤差异，我们通过检测血液中活性氧代谢物（ROMs）与总抗氧化能力（OXY）的含量开展了评估。此外，我们利用高速摄像机记录雄性斑姬鹟的逃逸飞行过程，以分析其飞行性能受影响的情况。最终，我们还收集了次年成鸟存活率、窝卵数及产卵日期相关数据。
3. ‘拔除飞羽的雄性斑姬鹟’每振翅一次的飞行距离缩短了5%，证实本实验处理确实降低了其飞行性能。与此一致的是，这类雄性的巢内育雏到访频次显著降低。然而，与实验雄性配对的雌性斑姬鹟，其巢内到访频次反而高于对照组雌性，并完全弥补了配偶减少的育雏投入。最终，两组间在投喂雏鸟的食物质量、成鸟或雏鸟体重，以及成功出飞的雏鸟数量上均无显著差异。雄性个体的氧化损伤程度及次年本地存活率均未出现组间差异。与之相反，与实验雄性配对的雌性斑姬鹟，其次年返回繁殖地的概率略低于对照组雌性，但该差异未达到统计学显著性。对于成功返回的个体而言，实验处理并未对其繁殖表现产生影响。
5. 本研究结果表明，雄性斑姬鹟的翅膀羽隙会降低其飞行性能，但在繁殖期出现该情况时，它们会通过减少育雏投入来优先保障未来的繁殖机会。因此，繁殖期内其身体状况并未出现明显损害。由于未参与换羽的雌性斑姬鹟能够弥补配偶减少的育雏投入，雏鸟也未即刻承受繁殖成本，但雌性个体可能会因存活率下降而付出相应代价。