Mule deer movements, survival, and use of contaminated areas at Rocky Flats, Colorado
Symonds, Kate K.
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Rocky Mountain mule deer (Odocoileus hemionus hemionus) reside on plutonium contaminated land that surrounds the Rocky Flats Nuclear Weapons Facility, Colorado. Concern exists over the potential for deer to transport radionuclides away from Rocky Flats. Deer may potentially transport radionuclides through excretion of contaminated forage and soil away from the ingestion site, or by retention of radionuclides in tissues or the hide. To assess their potential to transport radionulcides and to determine annual movement patterns, deer were radio-located throughout the year. Rocky Flats deer were year-round residents, seldom moved farther than 0.05 km from the buffer zone boundaries. At least 9 male yearlings left Rocky Flats, and yearlings are, therefore, the most likely age class for radionuclide transport. Based on annual movement patterns I observed, the potential for does and fawns to transport radionuclides off-site appears to be very low, although more data are needed to better assess movement patterns of yearlings. Two areas in the buffer zone contain detectable levels of radionuclides and are accessible to deer. I compared deer use to availability in these areas during winter and summer 1991. During winter, 45.3% and 52.0% of radio-collared does and fawns showed preference (P ≤ 0.027) for these 2 areas over non-contaminated areas. During summer, 39.0% and 36.7% of deer preferred (P ≤ 0.027) each area to non-contaminated areas. I also collected tissue samples from 7 vehicle-killed deer that were known to inhabit the buffer zone and submitted them for radionuclide analysis. All tissues had plutonium activities below detection limits. Again, transport of radionuclides appears to be very low, but because of small sample size, any conclusion regarding plutonium transport is premature. The deer population size was estimated from a helicopter survey during summer 1990, and from a ground survey during winter 1991. Population estimates were 161 (95% confidence interval 136-220) during summer, and 199 (95% confidence interval 198-207) during winter. Winter 1991 buck:doe ratio was 35:100, and fawn:doe ratio was 90:100. Annual adult doe survival rates were 0.792 ± 0.083 (SE) in 1990 (n = 24), and 0.857 ± 0.059 (SE) in 1991 (n = 35), and were not statistically different (P = 0.19). Winter survival rate for female fawns was 0.895 ± 0.043 (SE) (n=19), and male fawn survival rate for the same time period was 0.950 ± 0.046 (SE) (n=21), and did not differ statistically (P = 0.51). The major cause of mortality among radio-collared deer was collisions with vehicles (47.8%), and predation (21.8%). Accidents and unknown causes comprised the remainder of mortalities (30.4%).