DEN CHARACTERISTICS AND SURVIVORSHIP OF WOODRATS (NEOTOMA-LEPIDA) IN THE EASTERN MOJAVE DESERT

A population of desert woodrats (Neotoma lepida) in the eastern Mojave desert was studied for a period of three years. All 101 dens located within a 2.7 ha plot were identified, and trapped on a roughly bimonth ly schedule. Den occupancy rates (occupied dens/dens trapped) fell fro m a high of almost 50% at the initiation of the study to a level of ap proximately 5-10% due to the effects of a severe drought. Body mass of individuals remained roughly constant during this period, however, su ggesting that mortality was not due to starvation. Mean survival on th e site was 5.4 months, with no significant difference between the sexe s. Several characteristics of the den appeared to influence survivorsh ip, including the primary structural material and overall size. Occupa ncy and survivorship rates were significantly higher in Opuntia than i n other substrates, presumably because of increased predator protectio n. Reproductive output was strongly curtailed during most of the study . Woodrats reproduced only once in 1988, and not at all in 1989. The r eproductive failure coincided with a lack of annual plant production a nd seed set by perennials such as Yucca schidigera.