Meeting Abstract

69.3  Thursday, Jan. 6  Visual stimulation by blooming thistles accelerates changes in reproductive physiology in American goldfinches LULOFF, T.W.*; HAHN, T.P.; MACDOUGALL-SHACKLETON, S.A.; University of Western Ontario; University of California, Davis; University of Western Ontario tluloff@uwo.ca

Songbirds have been shown to respond to environmental information to accurately time reproduction to favorable conditions. Eastern American goldfinches (Carduelis tristis) begin breeding in late-July, simultaneous with seasonal temperature highs and the peak of flowering for many thistle species; a known food source for goldfinch young. To test the effects of temperature and visual stimulation of blooming thistles on reproductive physiology, we captured wild American goldfinches and housed them in a hot (23-28°C) or cold (7.5-11°C) temperature regime. Birds from each temperature group were exposed to either a blooming thistle, a non blooming thistle, or no thistle (control) and were photostimulated. Changes in testes size and concentration of plasma testosterone and luteinizing hormone were measured. There was no effect of temperature on testosterone concentration or testes size between groups throughout the experiment. However, we found that there was a significant effect of thistle. In the hot condition, there was a significantly greater testis size and testosterone concentration in birds exposed to a blooming thistle compared with a non-blooming thistle or the control group. There was no effect of thistle on testosterone concentration or testis size in the cold condition. These data indicate that goldfinches are stimulated by the presence of blooming thistles, and may in part explain the apparent delay in breeding cycle for this species.