Table 2 presents data on Pu and Am in small vertebrates from one Study Area, Area 11-C, NTS. Considerable variation is evident in Pu and Am levels in the three tissue components of each taxon. Perognathus longimembris, a granivore, and lizards, which are generally insectivorous, had relatively high mean Pu _ tissue burdens of 0.37 and 0.17 nCi/g ash, respectively, in the carcasses. These values are two orders of magnitude higher than the mean values in the granivore, D. microps, and the insectivore, 0. torridus. Mean concentrations in the carcass of A. Leucurus, an omnivore, are intermediate between the examples of high and low values given above. Highest Pu tissue burdens for any individual rodent (P. longimembris) were 132, 28, and 2.1 nCi/g ash for pelt, GI tract, and carcass, respectively. Considerable variation is also evident in Pu/Am ratios of two tissue components, pelt and carcass (Table 2). The GI tract is the only tissue component which had mean ratios which varied little between species representing several trophic levels and which had comparable ratios with those reported in soil and vegetation samples (Table 1). A more consistent pattern of ratios was expected at least between pelt and GI Both tissues are exposed tract of the same species from the same event site. to resuspendable contamination with Pu/Am ratios which should be consistent with those reported for soil and vegetation samples. The rodents examined all engage in dust bathing and utilize underground burrow systems for shelter. In addition, much locomotor activity of lizards exposes the ventrum to surface soil contamination, and both nocturnal and seasonal inactivity (hibernation) usually involves withdrawal to underground burrow systems. These burrow systems may provide significant soil contamination for both rodents, lizards, and major food items. Ingestion of foods provides additional sources of contamination from both vegetation and soil. Ratios of Pu/Am in food items such as plant parts and arthropods are unknown. Contamination, however, from soil is important for both food items, particularly insects and seeds, and in the form of soil particles which are commonly ingested with food by lizards. The variability in pelt or skin ratios of rodents and lizards is difficult to explain. For example, the mean Pu/Am ratio of the pelt of P. longimembris was significantly different (P<.01) than mean ratios found in other rodent pelts, soil, or vegetation (Tables 1 and 2). Differences in tissue ratios may indicate that some vertebrate species and individuals of the same species are exposed to varied physical-chemical forms of the radioisotopes and that these forms have not been characterized as to their concentrations or distributions within microhabitats frequented by smaller vertebrates. In addition, some variation in Pu/Am ratios found in small vertebrates may be due to morphological, physiological, and behavioral differences between species. For example, there is a wide range of body size in rodent species, from P. about 7 g to A. longimembris which weighs leucurus which weighs approximately 100 g. Body size in rodents is related to size of home range (McNab, 1963) and probably the range of microhabitats utilized by species. Table 3 is an initial attempt to group species in Area 11-C by similar ecological and spatial patterns. Animals are grouped by general trophic categories and activity strata from which they were collected. Area 11-C, as reported by Gilbert et al. The activity strata of (1975), were grouped into Low Activity Stratum (<25,000 CPM *41am) and High Activity Stratum (>25,000 cpM 2*1lam). 200