Kyle Davis ’19
Project Title – Song Sparrows: As Temperature Decreases Body Size Increase, Always?
Mentor – Dustin Reichard
There are 24 subspecies of song sparrows (Melospiza melodia) in North America. Most live in western North America with only three in the east. Bergmann’s Rule states that individuals within a species are larger in colder habitats, those closer to the poles. The size increase is well documented in western song sparrows (Melospiza melodia), but does Bergmann’s Rule apply to eastern subspecies as well. I sampled western subspecies: M. m. fallax (south), M. m. morphna (middle), and M. m. kenaiensis (north); and eastern subspecies: M. m. melodia in Georgia (south), New England (middle), and northeastern Canada (north). The tarsometatarsus was measured with digital calipers to find the mean length of 123 song sparrows. Mean tarsal length was compared across subspecies with ANOVA and in pairs with Bonferroni. In the west M. m. kenaiensis (24.8 mm) was the largest, morphna (22.6) intermediate, and fallax (21.8), the most southern, was smallest. Differences in the east were much less, north eastern Canada (22.2), New England (21.8), and Georgia (21.4). The western subspecies differ significantly (df = 116, 5; P<0.001 M. m. kenaiensis was significantly larger (P<0.001) than all other subspecies, none of which differed significantly from each other. Bergmann’s Rule describes variation in western subspecies only if the northernmost subspecies is included. In both western and eastern subspecies the insignificant cline follows the pattern predicted by Bergmann’s Rule.