Young females were implanted with testosterone propionate (TP) and estradiol benzoate (E2B) during several ontogenetic stages in an attempt to mimic the temporal scheme of the sexually dimorphic developmental steroid pattern of canaries. In males, higher estrogen levels are found during several ontogenetic stages as well as individually elongated periods of androgen secretion (Weichel et al. 1986). The steroid concentration of testosterone (T), dihydrotestosterone (DHT), and estradiol-17β (E2) during implantation and afterwards were analyzed by RIA. Songs were recorded to assess the hormonal influence on song organization of females. Parameters such as duration and frequency of tours were taken as behavioral indicators for song quality improvement. Besides observations of song organization, long-term monitoring of song activity was undertaken.
The following results were obtained:
- 1Control females did not sing frequently before their first breeding season. Vocalizations were comparable to subsong quality of very young males.
- 2E2B-therapies during several developmental stages in females revealed long-lasting influences on song behavior (2–3 months). The hormonal manipulations induced higher song activities, the song performances showing a more complex song organization than those of controls. Moreover, both effects remained for several months after the removal of the implants in spite of a sharp decrease in plasma titres of implanted hormones and unaltered secretion of other steroids analyzed.
- 3Early TP-implants did not result in a permanent alteration of song activity, although short-term effects could be registered.
- 4E2-pretreated females seemed to be more behaviorally sensitive to androgens. Tests of the behavioral sensitivity to TP as adults in relation to different pretreatment showed that the females which received estrogens as juveniles provided higher song activities in response to the androgen and showed shorter behavioral latencies towards TP. Additionally, birds of this specific treatment maintained spontaneous song behavior under long-day photoperiods (14L/10D), which is not the case in reproductively experienced females under similar light conditions.
Possible neural mechanisms underlying the behavioral responses to steroid treatment are discussed.