Graduate Thesis Or Dissertation
 

Population ecology of the Columbian white-tailed deer

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  • A population of Columbian white-tailed deer (CWTD) was studied on a refuge (790 ha) in southwestern Washington during 1972-77. Quality of habitat was considered good for these deer and total population size remained between 164-230 as determined by mark-recapture methods during November. Population size declined significantly between the winters of 1974-75 and 1975-76. All sex-age classes exhibited a contagious dispersion on the study area; the locations of high density areas among these classes differed slightly. Sex ratio at birth did not differ significantly from 1:1, but females outnumbered males 3:1 among yearlings and adults. Fawn:doe ratios ranged from 35-60 fawns per 100 does in November. From 1972-77, yearling and adult males comprised 18-21% of the November population, yearling and adult females 50-60% and fawns 21-31%. Limited data on reproduction indicated that all yearling and adult females bred and typically carried 2 fawns, while female fawns did not breed. There was a significant inverse correlation between recruitment rates of marked females (≥ 3.5 years old) and the population estimate for November of the previous year (r = -0.999, P<0.05). Winter mortality of yearling and adult males was significantly higher than expected and 77% of all fawn carcasses located were estimated to have died during summer. In 1975-76, female mortality was concentrated in a central portion of the study area where habitat quality had presumably declined. Median ecological longevity was 2.97 for males and 4.87 for females; median age at death was significantly greater for females than males. This was due to the higher mortality rate for males (0.345) than for females (0.179) at least 1 year old. Proximate causes of death included automobiles, bacterial infections, coyotes, dogs, drowning, nutritional stress and accidents. Based on the timing of mortality for males and females, stress due to breeding activities and fawning, respectively, were probably ultimate causes of death. CWTD were not migratory and exhibited remarkable sedentary tendencies. Mean home range size for females was 112.9 ha using the convex polygon method and 158.5 ha with the determinant method; for males, mean area of home ranges with each method was 137.7 ha and 192.2 ha, respectively. Home ranges tended to become smaller with increasing age among females, but larger with increasing age among males. Several marked females exhibited behavior that could be termed territoriality. Estimates of effective population size for this near-insular population ranged from 47-67, depending on which system of copulatory success we simulated for males. Although we detected no movement of deer onto the refuge, only about 1 immigrant per generation would need to breed successfully to eliminate fixation of genes due to random genetic drift. Stability of population size documented for this population could have been enforced by several negative feedback mechanisms that were suggested, but not substantiated, by the field data.
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