BOWEN, K.D.; Central Michigan University, Mt. Pleasant: Changes in Body Size and Color Pattern of the Northern Water Snake, Nerodia sipedon sipedon

Relatively small Nerodia sipedon sipedon possess a striking dorsal pattern, while relatively large snakes often have a more uniform dorsal coloration. Past researchers have hypothesized that this color shift occurs through a darkening of the ground color, but this hypothesis has never been tested quantitatively. Furthermore, it is not known if the ventral coloration of this subspecies changes with body size. I took digital images of the dorsum and ventrum of Nerodia sipedon sipedon individuals of all sizes from islands in Lake Michigan. I then used computer software to quantify the intensity of the dorsal blotches, dorsal ground color, and ventral coloration of each snake. Pearson�s correlation tests of color intensity and snake snout-vent length revealed that as snakes increase in length, the dorsal ground color darkens while dorsal blotches and ventral pattern show no statistically significant change in intensity. The potential costs and benefits of a change in dorsal coloration while ventral pattern remains relatively constant are discussed in terms of the needs of snakes of different sizes.