Meeting Abstract

P1.150  Tuesday, Jan. 4  Light Intensity, not photoperiod, stimulates the reproductive system of equatorial Rufous-collared Sparrows (Zonotrichia capensis) SMALL, TW*; MOORE, IT; University of Memphis; Virginia Tech twsmall@memphis.edu

Rufous-collared Sparrows breed in a wide variety of environmental conditions throughout their range and breeding phenology can be associated with local climatic variables. In the portion of their range surrounding the equator (Central Colombia to Southern Peru), populations often breed during the drier season and increased “sunshine” has been proposed as the primary environmental cue used to time reproduction in these areas. We conducted three experiments to test the role of light intensity and daylength in timing of breeding in equatorial Rufous-collared Sparrows. First, captive male and female sparrows exposed to either filtered natural light (lower light intensity) or filtered natural light augmented by electric lamps (higher light intensity). Second males were exposed to either direct sunlight (higher light intensity), or shaded sunlight (lower light intensity). After 23 days, males in both of the higher light intensity treatments had increased plasma testosterone concentrations and greater testis mass. Plasma estrogen concentrations and ovarian mass did not differ between females in the different treatment groups. Third, male and females were exposed to 8L:16D (SD) for at least seven weeks and then exposed to either continued SD or 20L:4D (LD) for six weeks. There was no difference between LD and SD treatments. The absence of a photoperiodic response differs from previous findings in Rufous-collared Sparrows from Costa Rica and Argentina. Together, these data suggest that different populations use different environmental cues to time reproduction in different parts of their range.