Characteristics of kangaroo rats, Dipodomys merriami, associated with differential predation risk

Between 1980 and 1990, 176 adult Merriam's kangaroo rats were subcutaneously implanted with radio transmitters and tracked for a total of 6316 animal-days at a California site, prior to and during reproductive seasons. Thirty-six animals are known to have been killed by predators, and 14 who disappeared abruptly are also presumed victims. These 50 cases permit various analyses of differential predation risk. Males incurred a predation rate (4·22 deaths per animal-year) more than twice that of females (2·01); this sex difference in mortality was apparently absent or reversed after the breeding season. Both male and female victims travelled significantly greater distances between successive radio-locations shortly before their deaths than surviving same-sex animals tracked contemporaneously. Rather than being selective for the feeble, predation on kangaroo rats is selective for the mobile.