Abstract
In breeding records for 12 species of small mammals from 9 families in 3 orders, individuals with an inbreeding coefficient of 0 were classified as noninbred, those with inbreeding coefficients greater than 0 as inbred. Juvenile mortality was defined as all deaths prior to ½ of the age of sexual maturity for each species. It was significantly higher for inbred than for noninbred animals in 11 of the 12 species using a 1-tailed sign test, and by Fisher's exact test in 3 species, Monodelphis domestica, Wiedomys pyrrhorhinos and Dolichotis salinicola. The higher mortality of inbred young of the species with the largest sample size, Elephantulus rufescens, was irrespective of litter size and of the parity of the dam.