STRAND, CR; SMALL, TW; DEVICHE, P; AZ St. Univ.; AZ St. Univ.; AZ St. Univ: Singing in the Rain: Growth of the song control system in free-ranging adult male Rufous-winged Sparrows, Aimophila carpalis

In most songbirds, exposure to increasing photoperiod in the spring stimulates the development of the reproductive system. Singing behavior in males increases as the reproductive system develops and circulating testosterone (T) concentration increases. Additionally, the brain regions that control singing (song control regions; SCRs) are larger during the breeding season, thus paralleling the development and regression of the gonads. However, in some birds, breeding is induced by environmental cues, such as late-summer monsoon rains rather than changes in photoperiod. For example, free-living male Rufous-winged Sparrows develop their testes in March due to increasing photoperiod, but have relatively low plasma T until after the monsoon rains begin, when they begin to breed. Since most research indicates that T is the main factor regulating SCR sizes, we hypothesized that SCRs would be smaller before the monsoon rains, when these birds normally have low circulating T, than after the rains, when T increases. To test this hypothesis, we captured adult male Rufous-winged Sparrows seven days before and 20 days after the monsoon rains began. We perfused birds in the field, collected their brains, and measured SCR volumes from sections immunostained for the neuronal marker NeuN. SCR volumes were larger after the onset of the monsoon rains. Similar to other songbirds, SCRs in male Rufous-winged Sparrows are larger during the breeding season. However, unlike in other species studies so far, SCR volumes increased as day length is decreasing. Comparative studies utilizing species that do not breed when day length is increasing can give new insight into the mechanisms regulating neuronal plasticity in the SCRs.