Effect of Weather on Individual Growth Rates in Cotton Rats, Sigmodon hispidus

Weather can influence many aspects of mammalian life histories through its impact on growth rates. We examined the seasonal effect of rain, mean temperature, snowfall, and snow cover on changes in body mass among individual young (≤60 g) and adult (>60 g) cotton rats (Sigmodon hispidus) in northeastern Kansas from March 1978 to December 1993. Weather significantly affected growth rates among all sex-season-size groupings except for young cotton rats in summer. In seasons other than summer, weather accounted for 53-68% of the variation in growth rates of young rats. Weather generally accounted for less of the variation in growth rates of adult cotton rats. When significant, snow cover was associated negatively and rainfall was associated positively with growth rates of all cotton rats. High temperatures in summer adversely affected growth rates of adult cotton rats but were associated with higher growth rates among all size-sex combinations in autumn. Growth rates of adult females in spring and adult males in autumn were highest at intermediate temperatures and lower at extremes. In autumn, response of growth rates of adult males to mean temperature varied with body mass. Intrapopulational variation in responses to weather may reflect different environmental and reproductive constraints at various points in the life cycle.