Reproductive Characteristics of Rodent Assemblages in Cultivated Regions of Central Argentina

Small mammals were trapped for 2 years at 16 localities on the central-Argentine pampa. Six species (Akodon azarae, Calomys musculinus, C. laucha, Bolomys obscurus, Oligoryzomys flavescens and Mus musculus) accounted for >95% of captures. The major breeding season, as assessed by pregnancies, was September or October through April or May. Mild weather in late autumn and winter of the second season resulted in a relatively longer breeding season during the 2nd year of the study. Females of all six species comprised significantly 50% of captures during the height of the breeding season. For most species, there was a negative correlation between embryo size and embryos per pregnancy; females with large embryos were poorly represented. C. musculinus had the longest breeding season; C. musculinus and Mus had the highest number of embryos per pregnancy; the two species of Calomys and Oligoryzomys had the highest percentages of pregnant females during the breeding season. The predominance of animals of smaller mass classes during the winter is thought to represent seasonal weight loss rather than juvenile recruitment.