Seasonal variation in the secretory lipids of the uropygial gland of a sub‐tropical wild passerine bird, pycnonotus cafer (L) in relation to the testicular cycle

Weight and lipid content of the uropygiai gland of male Pycnonotus cafer (Linnaeus), a common subtropical wild passerine bird exhibit seasonal variations, roughly coinciding with those of testicular activity. At the peak of the spermatogenic phase (June) and in the post‐breeding period (July, August) the gland becomes enlarged and contains a high amount of lipid, whereas during the long period of testicular quiescence (September through January) and in the progressive phase (February‐March) the glandular weight and lipid content decline considerably. The relative concentration of aliphatic monoester wax (plus sterol esters), which constitutes the major lipid component of the uropygial gland of this species, is high in the pre‐breeding, breeding and post‐breeding phases. The present findings apparently establish the dependency of the uropygial gland of the male wild passerine bird upon the seasonal fluctuation of its testicular activity, although the possible participation of thyroidal hormones and adrenal androgens in the maintenance of the basal level of activity of this organ during the period of testicular quiescence can not be ruled out.