BUSCH, D. Shallin*; WINGFIELD, John C.; University of Washington, Seattle; University of Washington, Seattle: Reproductive endocrinology of the song wren (Cyphorhinus phaeocephalus), a resident bird of the lowland tropics
In male tropical birds, levels of testosterone (T) are low and are often not as closely linked with breeding physiology and behavior as they are in temperate and arctic-breeding species. We explored the hormonal controls of reproduction in the song wren (Cyphorhinus phaeocephalus) during its breeding season (May-October) in the Republic of Panama (9°N, 79°W). Luteinizing hormone (LH), T, dehydroepiandrosterone, estradiol, and progesterone concentrations in males show no clear seasonal pattern at the population level. Mean T levels for male birds during the breeding season were low compared to species breeding in the temperate and arctic zones (mean=0.43 ng/ml, SE=0.06, N=26). To test the activity of the hypothalamo-pituitary-gonad axis, we injected male birds with gonadotropin releasing hormone (chicken 1). LH levels increased significantly 2-4 min after injection (p<0.001, Ncontrol=14, NGnRH=13), but T levels did not change 30 min after injection (p=0.50). In many avian species, using conspecific playback to simulate a territorial intrusion results in an increase in LH and T in the territorial male. We saw no relationship between T (N=26) or LH (N=65) and duration of conspecific playback with playback times ranging from 1-97 min. Our results show that the control of T release and potential role of plasma T levels in this species do not fit the paradigms developed with temperate and arctic-breeding species and are more in line with the results from studies on other lowland tropical species.
