Effect of overwintering adults on juvenile survival ofCalomys venustus(Muridae: Sigmodontinae)

The aim of this paper was to test the hypothesis that the presence of overwinteringCalomys venustusmales or females at the beginning of the breeding period reduced the survival of juveniles belonging to the first cohort of each year (C1). The study was carried out in four 0.25‐ha enclosures (two control and two experimental), each situated on natural pasture. This study was conducted between August 1997 and February 1999 and had two parts: removal of overwintering males (ROM) and removal of overwintering females (ROF). For the ROM treatment, overwintering males were removed immediately after C1 juveniles were born, in the ROF treatment overwintering females were removed after the C1 were weaned. Weekly censuses were taken for 3 successive days over 6 weeks. Juvenile survival was examined through a survivorship schedule. The survivorship values were compared by sex and treatment (removal of overwintering males or females) using repeated‐measuresanova. Removal of overwintering males and females did not improve the survival of C1 juveniles. This result could be related to the delay in maturation of C1 juvenile males.