Size Change in an Invasive Species

Schimmel/Conrades Science Center 167

Heat is generated by the body volume and lost across its surface. Therefore, larger homeotherms with their proportionately larger volume and smaller surface will withstand cold better than small homeotherms. Bergmann’s Rule is common expressions of body size change due to temperature change. We tested the relationship between body size and latitude in House sparrows (Passer domesticus) found in the Eastern United States. Due to the range of temperatures between each state, we expect a change in body size with larger birds being found in the north and smaller birds being found in the south. To test Bergmann’s rule, we measured the tarsometatarsal length and width. We also measured the bill length and width. We collected data from 801 House sparrow study skins collected from the Eastern United States. The tarsometatarsal length of House sparrows sampled was significant (ANOVA, p < 0.01). The change in width of the tarsometatarsus was not significant (ANOVA, P > 0.01). The bill length and width of House sparrows sampled was not significant (ANOVA, P > 0.01). The results suggest that changes in bill width, and length, and tarsometatarsal width is not effective at thermoregulation, but the change in tarsometatarsal length is effective in thermoregulation of House sparrows. The bill width did change, but the change in size was random, which suggests that the change in bill width is due to another variable such as seed strength.