The relationship between the ontogenetic pattern of sex steroids and the differentiation of sexually dimorphic song in canaries of both sexes was studied. Songs were recorded to assess the temporal course of different developmental stages. Song parameters such as length and frequency of tours were measured. Parallel to behavioural observations, all birds were bled regularly every 2&30 days from the age of 15 days to day 235. The plasma samples were analyzed by RIA to measure testosterone (T), dihydrotestosterone (DHT) and estradiol-17P (El). The following results were obtained: 1) In young male canaries we distinguish three different stages of song development: subsong, starting at the age of 30 days, plastic song, and juvenile autumnal song finally giving way to the rigid and stable utterances of the reproductive period in next spring. During ontogeny the length and frequency of tours increase gradually. Female canaries were not observed singing regularly during their first year of life, whereas males sing very frequently. 2) Both sexes show tendencies to elevated titres of testosterone before the onset of juvenile moult. These titres correspond to those of paired males during the reproductive cycle. Song development is not correlated with the ontogenetic pattern of testosterone: the process of crystallization from the amorphic songs uttered by juveniles progresses gradually to the autumnal song in late autumn, when the titres of T in males are low (< 200 pg/ml). Female T and D H T levels during ontogeny correspond to those of the males. 3) There are sex differences in the estradiol pattern. Males show higher titres in several stages of development than females.

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: Control females did not sing frequently before their first breeding season. Vocalizations were comparable to subsong quality of very young males. E2B‐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. Early TP‐implants did not result in a permanent alteration of song activity, although short‐term effects could be registered. E2‐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.

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