Serotonin Expression in the Song Circuitry of Adult Male Zebra Finches

•Serotonin and serotonin transporter expression are similar in the brain of zebra finches.•Different serotonin expression at different song nuclei in zebra finches.•Different serotonin expression at different peri-song nuclei in zebra finches.•Various forms of interactivity between serotoninergic and cholinergic neurones in the brain stem of zebra finches.•Different co-expression of serotonin in dopaminergic neurones in zebra finches.