Reproduction and growth in a precocial small mammal, Cavia magna
Journal of Mammalogy, 86:4, 763–772 (2005)
Small mammals usually produce large litters of altricial young,resulting in high reproductive rates. In contrast, cavies givebirth to few precocial young after a long gestation. The price ofthis reproductive strategy is a low intrinsic rate of naturalincrease. We investigated if the patterns of reproduction in awild population of Cavia magna are consistent with the hypothesesthat cavies can increase their reproductive output by breedingaseasonally and by maturing extremely early. We collected data onreproduction and growth by capture-recapture during a 26-monthfield study in a wetland in Uruguay, and from a laboratorypopulation founded with individuals from the same region. Amongthe Caviinae, C. magna is particularly precocial, with individualneonates weighing on average 18% of maternal mass. Reproductionwas mostly seasonal, with the main birth season starting at theend of September (austral spring) and extending until May in 1999and February in 2000, respectively, with only a few femalesreproducing during the 1st but not the 2nd austral winter.Individual females produced on average 3 litters per year. Somefemales born in early spring conceived successfully between theage of 30 and 45 days, similar to females in the laboratory. Theremainder of the 1st spring cohort and females of subsequent birthcohorts delayed reproduction until the following spring. Bodycondition and growth rates were highest in the spring, declinedthrough the year, and varied between years, and may be theproximate factors determining whether an adult female or ajuvenile initiates breeding. Breeding opportunistically wheneverconditions allow might partly compensate for the low reproductiverate of cavies.