Comparative Ecology and Life History of the Racer (Coluber constrictor) in Michigan

Abstract

The racer, Coluber constrictorfoxii, was studied over a six-year period in southeastern Michigan. The minimum age at maturity was 11 months in males and two years in females. Both sexes grew rapidly, exceeded 600 mm SVL at the end of the first full season of growth, and individuals of both sexes attained SVL >1300 mm. There was no sexual size dimorphism. Autumn body mass was correlated strongly with SVL (r = 0.994). There was a single clutch per year averaging 15.0 eggs, and clutch size was positively correlated with female SVL (r = 0.937). All hatchlings and some yearlings overwintered at dispersed locations, while some yearlings and all large adults overwintered at communal dens. Adults dispersed up to at least 2.2 km from major hibernacula. During the warm season, mean distance between recaptures was 424 m for large adults, 188 m for yearlings, and 62 m for small juveniles. These traits indicate high rates of energy acquisition and use. In contrast, adult survivorship appears to have been low, at an estimated 0.54 per annum. Adult and subadult survivorship appear to be uncertain because of winter frost penetration, consistent with a bet-hedging hypothesis explaining life-history differences among this population and those previously studied in Kansas and Utah. Published data on variation of body size throughout the geographic range of the racer were examined to test this hypothesis; small body sizes found in subspecies inhabiting relatively stable climatic regions were not consistent with the hypothesis. Instead, racer size and diet, and the presence of snake species with similar habits and diets, were correlated across the geographic range of the racer.