الفهرس 
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Abstract
Avian uropygial gland (preen gland or oil gland) is an exocrine gland that have been hypothesized to constitute an important defence against bacterial and fungal infections of plumage and skin in birds. Their secretion has been proposed to possess a potential odorant and/or pheromonal function (aids in the attraction of possible mates) as well as affecting the interaction between avian hosts and their ectoparasites. The uropygial gland secretion has been hypothesized to control populations of micro- and macro-parasites on the plumage of birds. It is predicted that the abundance of micro-organisms to be negatively related to the size of uropygial glands, and also the amount of secretions produced by glands. Experimental excision of the uropygial gland resulted in an increased level of fungi and bacteria on feathers and higher levels of feather degradation in individual birds with removed uropygial glands. Its active substance is a peptide bacteriocin. However, the active substances are not produced by the bird organism immediately, but by a specific bacterial strain.