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Abstract :
[en] Temperate-zone birds often display marked seasonal changes in reproductive behaviors and in the underlying hormonal and neural mechanisms. These changes have been extensively studied in canaries (Serinus canaria) and there is emerging evidence of variation among strains in physiological responses to seasonal cues. Fife fancy male canaries were previously shown to change their reproductive physiology in response to variations in day length but it remained unclear whether they display absolute refractoriness, as Border canaries do, or only display relative refractoriness or simply track day length to control gonadal activity, singing behavior and the associated neural plasticity. Male birds maintained on 8L:16D (SD) for 6 months that had become reproductively competent (high song output and large testes) were divided into two groups: control birds remained on SD and experimental birds were switched to long days (16L:8D). During the following 11 weeks, singing behavior (recorded and quantitatively analyzed for 3X2 hours everyweek) and gonadal size (repeatedly measured by CT X-ray scans) remained similar for birds in both groups except for trill numbers that increased in the experimental group. Prolonged exposure to SD had thus induced a nearly full activation of reproductive physiology and behavior. Day length was then decreased back to 8L:16D for experimental birds which immediately induced a cessation of song, a decrease in testes size and a decrease in the volume of song control nuclei (Area X, HVC, RA). These data demonstrate that Fife fancy canaries sharply respond to changes in photoperiod but only display relative photorefractoriness.