Long tail feathers of the barn swallow Hirundo rustica are a classic example of an intersexually selected trait, but previous aerodynamic analyses indicate that the tail feather is only 10–12 mm longer than the aerodynamic optimum even in the nominate subspecies with long tails. Here, by experimentally shortening female tail length, we studied the feeding cost of long tail feathers in Japanese barn swallows, Hirundo rustica gutturalis, which have ca. 10 mm shorter tails than the nominate subspecies. Female feeding rate was explained by the interaction between treatment and original female tail length: feeding rate decreased with decreasing original female tail length in control, but not in tail-shortened females. Because the interaction term was far from significant in the analysis of female incubation investment, the observed pattern would be specific to feeding rate, which is greatly affected by the aerodynamic properties associated with tail length. Differential allocation of paternal feeding investment was not observed in the current data set. Long tails would be costly at least in short-tailed females, supporting differential costs of ornamentation as predicted by sexual selection theory. Female outermost tail feathers are costly ornamentation in short-tailed Japanese barn swallows.

中文翻译：

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实验性尾巴缩短影响采食率取决于雌性谷仓燕子 Hirundo rustica gutturalis 的原始尾长

谷仓燕子 Hirundo rustica 的长尾羽是双性选择特征的典型例子，但之前的空气动力学分析表明，即使在具有长尾巴的指定亚种中，尾羽也仅比空气动力学最佳值长 10-12 毫米。在这里，通过实验缩短雌性尾长，我们研究了日本家燕 Hirundo rustica gutturalis 长尾羽的饲养成本，它们的长尾羽大约有。尾巴比指定亚种短 10 毫米。雌性摄食率通过处理和原始雌性尾长之间的相互作用来解释：摄食率随着对照中原始雌性尾长的减少而降低，但在尾巴缩短的雌性中则不然。因为交互项在女性孵化投资分析中并不显着，观察到的模式将特定于喂食率，而喂食率受与尾长相关的空气动力学特性的影响很大。在当前的数据集中没有观察到父亲喂养投资的差异分配。至少在短尾雌性中，长尾会很昂贵，这支持了性别选择理论预测的装饰差异成本。雌性最外面的尾羽是短尾日本家燕的昂贵装饰品。