Figure 1

A) The neural circuitry for song production and the motivation to engage in singing behavior. The motor pathway for song is demarcated by solid black lines. Song is initiated by motor sequences in HVC neurons that project to the premotor nucleus RA. RA innervates the hindbrain nucleus nXIIts that ultimately controls the vocal organ, the syrinx. The anterior forebrain pathway includes Area X, DLM, lMAN and RA and the circuit is indicated by the dashed black lines. The hypothalamic nucleus, POA projects to the ventral tegmental area (VTA) and the spinal cord. This circuit is essential for the motivation to engage in singing behavior and male copulatory behavior. B) A schematic diagram of the experimental treatment groups. Each row represents an experimental treatment group and the horizontal axis represents the experiment timeline measured in the number of days. Arrows indicate the time when starlings were transferred to a long day photoperiod. C) The mean (+/− SEM) testicular volume from starlings at the termination of the experiment. The change in volume provides a reliable marker for necessary photoperiodic manipulations of reproductive state. Letters indicate significant differences between treatment groups.