Animal coloration results from pigments, nanostructures, or the cosmetic use of natural products, and plays a central role in social communication. The role of cosmetic coloration has traditionally been focused in scenarios of sexual selection, but it could also take place in other contexts. Here, by using spotless starlings (Sturnus unicolor) as a model system, we explore the possibility that nestlings cosmetically use their intensely yellow-colored uropygial secretion to signal their genetic and/or phenotypic quality. In agreement with the hypothetical cosmetic use of the uropygial secretion, (i) video recorded nestlings collected secretion with the bill at the age of feathering, (ii) cotton swabs turned to the color of secretion after rubbing with them nestlings' gape, and (iii) gape and skin colorations correlated positively with that of secretion. Furthermore, we found that (iv) secretion coloration has a genetic component, and (v) associated positively with Vitamin E supplementation and (vi) with plasma carotenoid concentration, which highlights the informative value of nestling secretion. Finally, (vii) coloration of begging-related traits and of secretion of nestlings predicted parental feeding preferences. Consequently, all these results strongly suggest that the cosmetic use of colored uropygial secretion might also play a role in parent-offspring communication, complementing or amplifying information provided by the flamboyant colored gapes and skin of nestlings. The use of makeups by offspring for communication with relatives has been scarcely explored and we hope that these results will encourage further investigations in birds and other taxa with parental care.

中文翻译：

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用梳妆油制成的嘴揭示了八哥雏鸟的遗传和表型状况。

动物着色源于颜料、纳米结构或天然产品的化妆品使用，在社会交流中起着核心作用。化妆品着色的作用传统上集中在性选择的场景中，但它也可能发生在其他情况下。在这里，通过使用一尘不染的椋鸟 (Sturnus unicolor) 作为模型系统，我们探索了雏鸟在美容上使用它们强烈的黄色尾骨分泌物来表明它们的遗传和/或表型质量的可能性。与假设的使用 uropygial 分泌物的化妆品用途一致，(i) 视频记录了雏鸟在长羽毛时用喙收集分泌物，(ii) 棉签在与雏鸟的裂口摩擦后变成分泌物的颜色，(iii) 目瞪口呆和皮肤颜色与分泌物呈正相关。此外，我们发现 (iv) 分泌物颜色具有遗传成分，(v) 与维生素 E 补充呈正相关，(vi) 与血浆类胡萝卜素浓度相关，这突出了雏鸟分泌物的信息价值。最后，（vii）乞讨相关性状和雏鸟分泌物的颜色预测了父母的喂养偏好。因此，所有这些结果都强烈表明，有色尿臀腺分泌物的美容用途也可能在亲子交流中发挥作用，补充或放大由艳丽的有色间隙和雏鸟皮肤提供的信息。