The uropygial gland of the Great Cormorant (Phalacrocorax carbo): I. Morphology.

To further our knowledge of the basis of the wing-spreading behavior of cormorants, we compared the feathers of cormorants with a diving and a dabbling duck. Only the cormorant shows the division into a closed vane next to the rhachis and an open vane in the periphery of the feather. Macroscopically, the uropygial gland of the Great Cormorant (Phalacrocorax carbo) is bilobed, the papilla wears circlet feathers of type I. Histologically, the uropygial gland of the cormorant consists of tightly packed glandular tubules separated by internal septa. These tubules can be divided into three zones based on their laminar appearance. They transition into secretion-filled ducts that lead to the papilla. There is no central storage chamber. By contrast, the uropygial gland of the rock pigeon (Columba livia) contains a large central storage chamber, the glandular tissue is limited to the periphery of the gland. Thus, the histological organization of the cormorant uropygial gland is similar to many other aquatic birds. To elucidate the complex internal structure, we additionally reconstructed the uropygial gland three-dimensionally. [ABSTRACT FROM AUTHOR]