Diesters of 3-hydroxy fatty acids produced by the uropygial glands of female mallards uniquely during the mating season.

The uropygial gland secretions produced by female mallards (Anas platyrhynchos) throughout the year were analyzed by thin-layer chromatography and combined gas-liquid chromatography and mass spectrometry. Most of the year, the secretion was composed of wax esters. With the beginning of the mating season in the middle of March, a polar component appeared which became the dominant and sole component of the secretion through April and May and as the mating season ended in June, wax esters became the sole component of the secretion. The polar components were identified to be diesters of n-C8, n-C10, and n-C12 3-hydroxy acids with n-C16 and n-C18 alcohols and n-C6 to C16 even chain acids. Immediately after the diester-producing period the female uropygial glands produced very long chain wax esters composed of fatty acids longer than C12. By the end of August, shorter chain wax esters composed of C6 and C12 acids became the dominant components of the secretion and this composition, previously considered characteristic of mallards, remained constant until March. The observed disappearance of the short chain waxes during the postnuptial period is similar to that in males. The dramatic changes in the composition of the uropygial glands similar to those observed in the female mallards during the mating season have not yet been observed in any other species.