The uropygial gland of the Great Cormorant (Phalacrocorax carbo): II. Biochemical analysis of the uropygial secretion

Abstract

In contrast to many other water birds, the Great Cormorant, Phalacrocorax carbo (Phalacrocoracidae), shows a typical wing-spreading behavior after diving. This behavior has been linked to the partial wettability of the Cormorant’s feathers based on the unusual structure of the contour feathers. Close to the rachis, these feathers have a closed vane with very densely spaced barbs but have an open vane in more peripheral feather parts. To investigate whether the wettability is connected to the composition of the uropygial gland secretion that is often linked to water repellency of bird feathers, we analyzed the gland secretions of the Great Cormorant and, for comparison, of the Muscovy Duck, Cairina moschata (Anatidae). Using the mass spectrometry techniques, atmospheric solids analysis probe-atmospheric pressure chemical ionization-mass spectrometry (ASAP-APCI-MS) and gas chromatography/mass spectrometry (GC/MS), significant differences in the chemical composition of the secretions were revealed. The Cormorant showed a highly diverse mixture of more than 1000 compounds consisting of methyl-branched aliphatic carboxylic esters with large chain length variability. In contrast, the duck’s secretion is dominated by the two esters octadecyl and eicosyl 2,4,6-trimethyloctanoate. Water contact angle measurements of the secretions showed that the secretion of the Muscovy Duck has higher water repellency than that of the Great Cormorant. Nevertheless, contact angle measurements of feathers before and after removing of feather waxes indicate that these waxes, likely consisting of the uropygial gland secretions, did not influence water repellency of the feathers to a large degree.

White Roman Goose Feather-Inspired Unidirectionally Inclined Conical Structure Arrays for Switchable Anisotropic Self-Cleaning

“…White Roman geese (Anser anser domesticus ) are web-footed aquatic birds adapted for surface swimming (Figure a). Their feathers are coated with gland-secreted preening oils, consisting of a variety of water-repellent carboxylic acid esters and wax-type esters. , The application of preening oils makes the feathers maintain a long-term nonwetting performance with an average static water contact angle of 151.4 ± 1.3° (Figure b). The corresponding superhydrophobicity is derived from the integration of hydrophobic lipids and intricate hierarchical structures, composed of numerous oriented barbules that branch from barbs (Figure c).…”