Androgens and Mating Systems: Testosterone-induced Polygyny in Normally Monogamous Birds

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Abstract
Recent investigations of the plasma profiles of testosterone (T) in free-living birds suggest that circulating levels of T during the reproductive cycle remain elevated longer in males of polygynous species than in males of monogamous species. When the hormonal profile of polygynous males is mimicked by the administration of subcutaneous implants of T to males of monogamous species, thus maintaining plasma levels of this androgen at high vernal levels, frequencies of territorial aggression and courtship behavior remain elevated, resulting in a marked increase in the size of the territory. A substantial number of T-implanted males also become polygynous, attracting two and sometimes three females to settle on their enlarged territories. These data suggest strongly that the nature of avian mating systems is regulated proximately by temporal patterns of hormone secretion.