Plasma levels of luteinizing hormone and androgens in relation to age and breeding status among cooperatively breeding Australian magpies (Gymnorhina tibicen Latham).

Plasma levels of luteinizing hormone (LH), testosterone (T), and 5 alpha-dihydrotestosterone (DHT) were measured in relation to age and social/breeding status among free-living male Australian magpies. Magpies live in territorial groups of up to 20 individuals and due to a largely age-related dominance hierarchy among males, many individuals are prevented from breeding. Adult plumage is not attained until the fourth year, but males can produce motile sperm in their first year. Plasma levels of LH and T peaked just prior to egg-laying among breeding males, but DHT levels remained steady or declined slightly during the breeding period. Adults (greater than 3.5 years) had significantly higher levels of both LH and androgens than did subadults (less than 3.5 years) during the breeding season. Nonbreeding adults had similar levels to those found among the breeding adults, but breeding subadults had higher levels of both LH and androgens than the nonbreeding subadults. These results are interpreted in terms of the opportunities for each of these classes to obtain copulations and are discussed in relation to age-related hormonal secretion in other species.