ENTRAINMENT PROPERTIES OF THE CIRCADIAN SYSTEM CHANGING WITH REPRODUCTIVE STATE AND MOLT IN THE CANARY

Changes in entrainment properties of the circadian pacemaking system w ith respect to changes in reproductive state and molt were investigate d in the male domestic canary (Serinus canaria). In two experiments ca naries were subjected to three and two similar sequences of light regi mes, respectively, during 1 year. Locomotor activity, feeding, and voc alization were simultaneously recorded. Only birds showing complete po stnuptial wing feather molt and related changes in behavior (vocalizat ion) expressed differences in the ability of their circadian system to entrain to low-amplitude light/dark (LD) cycles with periods (T) > 24 h. It is suggested that changes in the organization of the circadian system, including differences in entrainment properties, are associate d with the state of photorefractoriness and related functions (testicu lar regression, postnuptial molt). Regardless of the molt status, over 90% of the birds that were arrhythmic in constant light (LL) entraine d to low-amplitude LD cycles with T 25.5 h (Experiment 1) or T 25.0 h (Experiment 2). Birds that did not entrain or were relatively entraine d with the respective light regimes were (with one exception) rhythmic in LL. It is therefore likely that the occurrence of arrhythmia in LL facilitates entrainment to low-amplitude light cycles.