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Wax esters constitute the major products of the uropygial glands of male mallard ducks (Anas platyrhynchos). Combined gas-liquid chromatography and mass spectrometry of the acyl and alcohol portions of the wax ester revealed dramatic seasonal variation. Of the total of nearly 100 compounds detected in the acyl portion, more than 90 were identified as n-, monomethyl-, dimethyl-, and trimethyl-C6 to C20 acids. The major components were 2-methyl- and 4-methyl C6 acids which constituted nearly 75% of the total acids during most of the year. As the birds went through the post-nuptial molt into eclipse, these short chain acids decreased to only 4% of the total acids. Fatty acids longer than C12 became the major components during the summer months when the birds were in eclipse and by fall the characteristic shorter branched acids reappeared as the dominant components. Fatty alcohols did not undergo such dramatic changes. This is the first report of biochemical changes that occur during eclipse.

The poll glands of the camel have been studied histologically and histochemically. An active gland, as observed between September and March, with a peak period in November and December, consists of sharply demarcated lobules separated by thin strands of connective tissue. Alveoli and proximal parts of excretory ducts are either lined with flat/simple cuboidal epithelium or with tall cells possessing distal protruding tips almost occluding the lumina; both segments, i.e. alveolus and proximal part of excretory duct, are therefore secretory. In the inactive gland there is an apparent increase in the interlobular stroma with massive deposition of collagenous fibres. The alveoli are lined with squamous to low columnar epithelium. The structural appearance in the castrate animal is essentially the same as that of the inactive gland except for its remarkable amount of interlobular tissue. Both delta 5-3 beta- and 17 beta-hydroxysteroid dehydrogenases have been demonstrated histochemically in the secretory portions of the gland. Their activity is restricted to the period between September and March and is comparatively highest during November and December. It is concluded that the morphological, enzymatic and secretory activities of the poll gland are correlated with testicular activity and rutting behaviour. It is suggested that the poll glands could be a source of sex pheromones.