The song control nucleus HVC undergoes neuronal replacement throughout adulthood. New neurons are incorporated into functional circuits, responding to auditory stimuli within 1 month of their formation (Paton and Nottebohm 1984). These neurons live for weeks to months before being replaced. Prior work has shown that the number of labeled neurons still present in HVC 4 months post-birthdating declines with age in adult male zebra finches that are between 5 mos-3 years old at the time of cell labeling. (Wang et al. SFN #646.15, 2001). The goals of this study were to determine 1) whether this age effect is present when new neurons are first incorporated into HVC or emerges subsequently due to age-dependent changes in cell death, and 2) whether the age effect is influenced by auditory experience. Birds were deafened by cochlea removal. Two weeks later, deaf and age-matched hearing controls were given BrdU (10 mg/ml, 75 µl injections, 3x day, 4 days). Bird ages at the time of injection were 3-21 mos. Birds were...