Uropygial gland secretions are used as cosmetics by some species of birds to color and enhance properties of feathers and teguments, which may signal individual quality. Uropygial secretions also reach eggshells during incubation and, therefore, may influence the coloration of birds’ eggs, a trait that has attracted the attention of evolutionary biologists for more than one century. The color of hoopoe eggs typically changes along incubation, from bluish-gray to greenish-brown. Here, we test experimentally the hypothesis that dark uropygial secretion of females is responsible for such drastic color change. Moreover, since uropygial secretion of hoopoes has antimicrobial properties, we also explore the association between color and antimicrobial activity of the uropygial secretion of females. We found that eggs stayed bluish-gray in nests where female access to the uropygial secretion was experimentally blocked. Furthermore, experimental eggs that were maintained in incubators and manually smeared with uropygial secretion experienced similar color changes that naturally incubated eggs did, while control eggs that were not in contact with the secretions did not experience such color changes. All these results strongly support the hypothesis that female hoopoes use their uropygial gland secretion to color the eggs. Moreover, saturation of the uropygial secretion was associated with antimicrobial activity against Bacillus licheniformis. Given the known antimicrobial potential of uropygial secretions of birds, this finding opens the possibility that in scenarios of sexual selection, hoopoes in particular and birds in general signal antimicrobial properties of their uropygial secretion by mean of changes in egg coloration along incubation.
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Jorge Doña Reguera, Ana Belén García Martín, Jonathan Romero Masegosa, and Manuel Soto Cárdenas helped in caring for the captive breeding population. Estefanía López Hernández helped with the laboratory tasks. Comments and suggestions by Magdalena Ruiz Rodríguez and two anonymous reviewers on a previous version greatly improved the understanding of the paper. Support by funding was provided by Spanish Ministerio de Ciencia e Innovación, European funds (FEDER) (CGL2005-06975/BOS, CGL2009-14006, CGL2010-19233-C03-01 and CGL2010-19233-C03-03) and Junta de Andalucía (P09-RNM-4557).
The experiment was conducted according to relevant Spanish national guidelines (Real Decreto 1201/2005, de 10 de Octubre) and under the permission of Junta de Andalucía, Dirección General de Gestión del Medio Natural which authorized the establishment and maintenance of the captive breeding population (Resolución de 14 de Abril de 2008) and conceded the permits required to perform the present research according to Spanish regulations (Resoluciones de 14 de Abril de 2008 and 23 de Marzo de 2010).
Juan J. Soler and M. Martín-Vivaldi contributed equally to this work.
Communicated by: Alexandre Roulin
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Soler, J.J., Martín-Vivaldi, M., Peralta-Sánchez, J.M. et al. Hoopoes color their eggs with antimicrobial uropygial secretions. Naturwissenschaften 101, 697–705 (2014). https://doi.org/10.1007/s00114-014-1201-3
- Egg color change
- Sexual signal
- Uropygial gland secretion