Dispersal Behavior in Female White-tailed Deer

Open Access
Author:
Lutz, Clayton Lee
Graduate Program:
Wildlife and Fisheries Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 05, 2015
Committee Members:
  • Duane R Diefenbach, Thesis Advisor
  • C Paola Ferreri, Thesis Advisor
  • Michael John Sheriff, Thesis Advisor
  • Christopher S Rosenberry, Thesis Advisor
  • Michael Gerard Messina, Thesis Advisor
Keywords:
  • barriers
  • chronic wasting disease
  • disease spread
  • dispersal
  • foray
  • movement
  • Odocoileus virginianus
  • Pennsylvania
  • proximate causes
  • ultimate causes
  • white-tailed deer
Abstract:
Dispersal is a common life-history trait across taxa and is ecologically important because it influences gene flow, population dynamics, colonization, and the spread of disease. The reasons animals disperse can be separated into two categories: proximate and ultimate causes. Proximate causes provide cues for dispersal to occur and can influence the characteristics of the dispersal event. Ultimate causes of dispersal refer to the evolutionary advantages of dispersal and why dispersal persists on the population level. Documenting an organism’s dispersal behavior and identifying factors that influence that behavior are crucial not only to understanding the basic ecology of a species, but also for providing critical information for the conservation and management of that species. Although dispersal is an important component of white-tailed deer (Odocoileus virginianus) ecology and management, it remains understudied and most analysis has focused on the dispersal of males. I investigated dispersal behavior patterns in female white-tailed deer to better understand proximate and ultimate causes of dispersal. Proximate cues influence important features of dispersal behavior, including when dispersal occurs, how long it lasts, and the direction, straightness, and distance of the dispersal path. I tracked 229 radiomarked (VHF collars, n = 204; GPS collars, n = 25) juvenile female white-tailed deer in 4 study areas in Pennsylvania to evaluate dispersal behavior and to determine proximate cues that influence dispersal. I observed dispersal in all 4 study areas, with an overall dispersal rate of 11.8%. Female dispersal largely occurred at 1 year of age with an average dispersal date of 6 June, which coincides with the fawning season. Dispersal paths varied, but were generally non-linear (average straightness = 0.579), long distanced (average dispersal distance = 18.0 km), and prolonged (average duration = 355 hrs). Physical landscape features (i.e., roadways, rivers, residential areas) were important influences on changing dispersal path direction and influencing where dispersal terminated, however topography did not influence dispersal direction. Additionally, forays outside the natal range that did not result in dispersal were recorded in 52% of GPS-collared deer during the dispersal period. Our results suggest that dispersal behavior in female deer is influenced by both intra-specific social interactions, particularly during the fawning season, and physical landscape features. The characteristics of dispersal behavior can provide insight into the ultimate causes and evolutionary strategies of dispersal. Hypotheses for the ultimate cause of dispersal suggest it is a beneficial strategy for the disperser because it reduces competition for local resources, reduces competition for breeding partners, and reduces the potential for inbreeding. Dispersal behavior in white-tailed deer predominantly occurs in 1-year-old males; however, females of the same age also disperse. The timing of female dispersal during fawning season and low dispersal rates suggest that competition for mates and reduced inbreeding are not ultimate causes of female dispersal, as suggested for males. I proposed that female dispersal is the result of competition for space when pregnant females seek to isolate themselves before and after parturition. To test this hypothesis, I conducted a meta-analysis of female dispersal rates from 12 populations of white-tailed deer and predicted dispersal rate and distance were positively related to deer density. I found a positive relationship between dispersal rate and deer per forested km2 and between dispersal distance and deer per forested km2. These results are consistent with the hypothesis that female dispersal is density dependent and caused by the exclusion of subordinate 1-year-olds as adult females seek isolation before and after parturition.