Survival of Columbian White-Tailed Deer in Western Oregon

Abstract

Columbian white-tailed deer (Odocoileus virginianus leucurus; CWTD) are an endangered subspecies on which little demographic information exists. We determined survival rates and causes of mortality for 64 radiocollared adults from 1996 to 1998, and for 63 radiocollared neonatal fawns during the summer and fall months of 1996-2001 in Douglas County, Oregon, USA. Annual adult survival rates averaged 0.74 over 3 years, and most mortality (73%) occurred between fall and winter. Seasonal survival was lowest (0.75) for the fall-winter 1997-1998, and was ≥0.90 during all spring-summer periods. Annual and seasonal survival rates did not differ by gender. Average annual survival was 0.77 for deer in wildland areas compared with 0.66 for deer in suburban areas, but these differences were not consistent between years and seasons. Survival over the entire 3-year study was low (0.38). Eight deer died from a combination of emaciation and disease, and almost all (92%) necropsied deer were in poor body condition. Fawn survival to 7 months was low (0.14, 95% CI = 0.02-0.26) and declined most rapidly during the first 1.5 months of life. Predation (n = 21) and abandonment (n = 6) were the most frequent known causes of death for fawns. Our results suggest that CWTD may have responded to density-dependent factors during this short-term study, although the effects of other environmental or intrinsic factors cannot be ignored. Fawn survival may be insufficient to produce enough recruits for population growth and eventual range expansion.