Status and habitat use of Columbian white-tailed deer in Douglas County, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/q811km85g

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  • A study conducted May 1978-December 1980 determined that the present geographic range of Columbian white-tailed deer, Odocoileus virginianus leucurus, (CWTD) in Douglas County, Oregon encompassed 1199km2. The area was predominately a Quercus woodland community, typical of the Interior Valley Zone of western Oregon. The CWTD distribution was not contiguous throughout its range; the highest densities occurred along the North Umpqua River between Glide and Wilbur. Ten habitats were described: grassland, grass-shrub, oak-savanna, open oak, closed oak, oak-conifer, oak-madrone, madrone, riparian and conifer. CWTD exhibited a preference (P<0.05) for grass-shrub, oak-savanna, open oak, closed oak, riparian and conifer habitats while selecting the remaining habitats less frequently (P<0.05) than was expected from corresponding availabilities. Grassland use increased proportionally with biomass production of grasses and forbs during the spring and with mean monthly precipitation in the fall; CWTD utilized grasslands more frequently (P<0.05) during the fall than in the spring. Fawns utilized. woodland and brushland habitats more frequently (P<0.05) than yearlings and adults; yearlings utilized grasslands more often (P<0.05) and grassshrub habitats less frequently (P<0.05) than adults. Adult males occurred less frequently (P<0.05) in grass-shrub and more often (P<0.05) in conifer habitats than adult females, particularly in the summer. The population estimates for the 2745 ha study area were 628 and 740 CWTD representing an average density of 22.9 and 27.0 CWTD per km2, respectively. There existed a positive association (P<0.05) between distribution and abundance of CWTD and the juxtaposition of suitable habitat to the North Umpqua River. A positive curvilinear relationship between CWTD density and percent woodland cover was observed; maximum densities occurred in areas supporting approximately 50% woodland cover. Fall herd composition estimates were 52 fawns and 30 bucks per 100 does. Secondary sex ratios departed from unity (P<0.05) favoring males when summer rainfall was abnormally low. Malnutrition and vehicle-inflicted injuries accounted for the largest proportion of known mortality. The ultimate cause of mortality among yearling and adult males and females was apparently associated with reproduction; these activities were more demanding (P<0.05) on males. The median age at death for males (1.65) was less (P<0.05) than that observed for females (2.15). Fawn survival and recruitment varied inversely with existing population densities and winter severity. Parasite loads were light and corresponded with observed seasonal differences in the physical condition of CWTD. Convex polygon estimates of home range size for CWTD females and males averaged 21.1 ha and 32.8 ha, respectively. Elliptical home range estimates were invariably larger than corresponding convex polygon estimates and averaged 44.5 ha and 47.1 ha for females and males, respectively. Home ranges were stable between years; however, males and females demonstrated significant shifts in center of activity among the seasons, behaviors observed to be associated with rutting and fawning activities, respectively. CWTD and black-tailed deer demonstrated a local geographic and ecological segregation; there was a significant inverse correlation in the relative densities of the two species, and sympatric populations of black-tailed deer and CWTD differed (P<0.05) in their frequency of occurrence among the ten habitats. Local geographic distributions and habitat-use patterns indicated that within preferred habitats, CWTD competitively excluded black-tailed deer. Lowland riparian systems played a major role in CWTD ecology, representing an important environmental component in the life history of the species and serving as corridors of dispersal and recent geographic expansion.
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