In anticipation of the breeding season male songbirds of the temperate zones undergo gonadal recrudescence in early spring that lead to elevated circulating testosterone (T) levels, positively correlated with an increase in aggressive and song behaviour. However, besides seasonal changes there are also marked fluctuations of T levels and song production within the breeding season. In many species, T levels and singing activity drop after pairing or after the first clutch is laid. Domesticated canaries (Serinus canaria) are multiple-brooded with an extended breeding season, and males continue to sing after egg-laying. So far, studies have mainly focused on the seasonality of T levels and song behaviour whereas the pattern of change throughout the breeding period is unknown. Here, we focused on the first and on the last brood of the breeding season. We measured plasma T levels in males at the different breeding stages and assessed song characteristics of males at both times. T levels fluctuated significantly throughout brood 1, being highest during the nest building stage compared with egg-laying and feeding of young. No such changes occurred during the last brood. Temporal song characteristics changed between brood 1 and brood 3 with song length being the main contributor to explain these changes. Our data suggest that T mainly plays a role in mate attraction and initial nesting site selection but that elevated levels are not necessary for subsequent breeding attempts. Furthermore, temporal song characteristics are maintained independently of T levels, suggesting a threshold effect. Our results demonstrate behavioural and physiological plasticity of domesticated canaries during the breeding season and are consistent with previous findings in wild songbirds.