A Population Model for Deer on the Hopland Field Station, Mendocino County, California

Average numbers of black-tailed deer (Odocoileus hemionus columbianus (Richardson)) on the 5,000-acre University of California, Hopland Field Station, Mendocino County, California from 1964 through 1966 were calculated from herd composition, hunter kill, carcass examination, trapping, and autopsy data. Herd composition counts indicated average October ratios of 17 legal bucks, 17 spike bucks, and 67 fawns per 100 does. Two estimates of the October population were calculated from these ratios--one based on the age composition of the legal buck kill and the other on replacement of legal buck mortality. The average of these two estimates was considered to be the most reliable estimate of the October (post-hunting) population, and was adjusted from mortality and natality data to obtain estimates for April (pre-fawning), May (post-fawning), and July (pre-hunting). Minimum populations of 740, 690, 600, and 480 deer in May, July , October, and April respectively appeared to be required to support the annual known mortality of 41 legal bucks during the 3-year study period, assuming that the average birth rate, sex and age composition, and mortality ratios in the population were accurately determined. These estimates indicate an annual mortality rate of 35%. The mortality rate attributable to hunting of legal bucks during the regular deer season was estimated to be 5%, while a.n additional 10% was removed by trapping and collecting for research purposes. This annual man-caused mortality, amounting to slightly less than half of the total estimated mortality, appears to stimulate a higher fawn survival rate than that observed elsewhere in Mendocino County where legal hunting is limited to adult males. It is suggested that deer populations in this area can sustain much higher harvest levels than those currently achieved by the exclusive hunting of adult males.