SMALL, Thomas W *; DEVICHE, Pierre; SHARP, Peter; Arizona State University; Arizona State University; Roslin Inst., Scotland: Conspecific and Heterospecific Song Exposure Accelerates Photoinduced Reproductive Development in the Flexibly Breeding Rufous-winged Sparrow, Aimophila carpalis

In most birds, annual changes in day length control seasonal reproductive development and regression. For example, photostimulation induces testicular development in captive Rufous-winged Sparrows, a resident of the Sonoran desert. The testes of wild Rufous-winged Sparrows also develop in the spring, when photoperiod increases. However, plasma luteinizing hormone (LH) in these sparrows does not increase with photostimulation. Rufous-winged Sparrows usually reproduce after monsoon rains in July and August, when their testes further enlarge and their plasma LH increases despite decreasing photoperiod. Wild males sing more after monsoon rains, and in captivity, plasma LH is highest in males who can hear numerous other males. We hypothesized that exposure to conspecific song stimulates the reproductive system. We exposed 21 adult male Rufous-winged Sparrows to short days (8L:16D) for eight weeks. We then divided birds into three groups (n=7). One group (CON) was exposed to no song recording during the experiment. The remaining groups were exposed either to conspecific song (CSP) recordings or to heterospecific song (HSP) recordings (Black-Throated Sparrows, Amphispiza bilineata, also a Sonoran desert resident) for two hours a day. After two weeks, all birds were transferred to long days (13L:11D) for five weeks with continued daily song exposure. At the end of this period, CSP males had larger testes than HSP males and CON males, and HSP males had larger testes than CON males. Thus, conspecific and to a lesser extent heterospecific song exposure promoted long-day induced testicular recrudescence, demonstrating a role for social, non-photoperiodic factors in the control of reproductive development.