Open Access
Christensen, Sonja Ann
Graduate Program:
Wildlife and Fisheries Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 06, 2009
Committee Members:
  • Duane R Diefenbach, Thesis Advisor
  • white-tailed deer
  • resource selection
  • Habitat use
  • sika deer
Concerns on behalf of National Park Service resource managers regarding ungulate herbivory on Assateague Island National Seashore (ASIS) prompted this descriptive study on the population ecology of both the native white-tailed deer (Odocoileus virginianus) and the non-native sika deer (Cervus nippon) that inhabit the island. Sturm (2007) conducted an exclosure study to document the effect of feral horse (Equus caballus) herbivory, deer herbivory, and horse and deer herbivory combined on plant communities. Sturm (2007) found that herbivory on some species could be directly attributable to either horse or deer. However, the effects of sika (Cervus nippon) and white-tailed deer (Odocoileus virginianus) herbivory could not be separated via an exclosure study design because of the difficulty of passively excluding one deer species but not the other. Thus, this research project was conducted to describe habitat use of sika and white-tailed deer and possibly attribute herbivory on some plant species to specific deer species if spatial separation in habitat use could be identified. I captured white-tailed deer and sika deer in January–March of 2006 and 2007 throughout the Maryland portion of Assateague Island. Deer were fitted with radio-collars and their survival and locations monitored via ground telemetry. Up to four locations were acquired per deer each week during early (May–June) and late (August–September) growth periods for vegetation on the island. Also, I estimated deer locations during a dormant vegetation period (November¬–December 2006). I used these data to estimate survival and harvest rates, document movements, and model habitat use. I captured and fitted 50 deer with radio-collars over the course of the study. Of these 50 deer, 36 were sika and 14 were white-tailed deer. Of the 36 sika deer, 10 were harvested, three were likely killed by hunters but not recovered, and one died of natural causes while giving birth. Of the 14 white-tailed deer, three were harvested, one was illegally killed, and two were censored because of study-related mortality. Annual survival was 0.48 (95% CI = 0.16–0.82) for male white-tailed deer, 0.74 (95% CI = 0.44–0.91) for female white-tailed deer, 0.56 (95% CI = 0.35–0.75) for male sika deer, and 0.86 (95% CI = 0.70–0.94) for female sika deer. The harvest rate was 0.12 (95% CI = 0.04–0.27) for female sika deer, 0.44 (95% CI = 0.25–0.65) for male sika deer, 0.18 (95% CI = 0.05–0.51) for female white-tailed deer, and 0.38 (95% CI = 0.10–0.78) for male white-tailed deer. Annual survival rates for both species were similar to what has been observed in other populations. Unfortunately, small sample sizes for male white-tailed deer limited inferences about harvest and survival rates, but harvest rates of females for both species were similar to other published studies. Hunting was the primary cause of mortality, and outside the hunting season survival was 0.98–1.00 for all species and sexes. I found that the home range area of sika deer was much greater than the home range area of white-tailed deer, but failed to detect any difference between sexes or among seasons. Sika deer also made long-distance movements and left the Maryland portion of Assateague Island. No sika deer left Assateague island during our study, but I did document the dispersal of a male white-tailed deer to the mainland. In their native range, sika deer have been able to readily expand populations and occupy vacant habitat (Kaji et al. 2000 and Kaji et al. 2004). The long distance movements I observed on Assateague Island, especially relative to white-tailed deer, may reflect the ability of this species to exploit food resources that may be limited in quality or quantity, or both. However, I did not collect data to assess use of food resources by sika deer and whether this may have influenced long distance movements. I found both species of deer were less likely to use a habitat the further it was located from cover, which was defined as tall shrub or forest vegetation. For every 10 m from cover each species of deer was 1.23–1.38 times less likely to use any given habitat. Patterns in use of vegetation classes were similar across species and seasons. Relative to forest habitat, both species avoided dune herbaceous, disturbed lands, sand, and water categories. Both species neither avoided nor preferred developed herbaceous, low shrub, marsh herbaceous, and tall shrub categories compared to the forest category. However, there were consistent differences between the two species. During spring white-tailed deer were more likely than sika deer to use forested, tall shrub, disturbed herbaceous, and sand areas, but were less likely to use all other habitats. During summer, habitat use was similar between the two species except that white-tailed deer tended to use forested habitat more. During winter, white-tailed deer were less likely to use dune herbaceous, low shrub, and forested habitats than sika deer.