Dispersal timing, distances, and rates of Pennsylvania black bear
Open Access
- Author:
- Vreeland, Wendy Christine
- Graduate Program:
- Wildlife and Fisheries Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 14, 2015
- Committee Members:
- Duane R Diefenbach, Thesis Advisor/Co-Advisor
- Keywords:
- black bear
dispersal rates
dispersal distances
dispersal timing
Pennsylvania
population density
range expansion - Abstract:
- In Pennsylvania, the black bear (Ursus americanus) population has expanded its range since the early 1980s. I investigated if dispersal timing, distance, and rates changed compared to previous research, and if those changes corresponded with range expansion and increasing population density. I used records of bears captured and ear-tagged <16 months of age with specific locations of tagging and recapture or dead recovery encounters (n = 466). I classified bears as dispersed if the measured distance between initial capture and final recovery was ≥13 km, which was the greatest linear distance across the average female bear home range in Pennsylvania. Based on this criterion, I classified <5% of bears as dispersing <16 months of age and dispersal occurred at 16–19 months of age. I estimated dispersal rates using logistic regression models, to investigate if dispersal differed by region or decade for males and females. Median distance dispersed was greater for males (47.03 km, n = 98) than females (25.84 km, n = 70). Region of Pennsylvania and decade were not related to the distance bears dispersed. Overall, male dispersal rate was 0.67 (SE = 0.06) and female dispersal rate was 0.28 (SE = 0.06). For males, I found that dispersal rates were 0.48 in the 1980s and increased to >0.75 in the 1990s and 2000s but did not vary by region of Pennsylvania. No single logistic regression model best explained female dispersal so I used model averaging to estimate dispersal rates by decade and region. The greatest increase in female dispersal rates occurred between the 1990s and 2000s in all regions. My results indicated a greater dispersal rate, at greater distances, for female bears than previous research in Pennsylvania but dispersal characteristics of males were similar to previous research. My results indicated that dispersal by females, especially at the edge of the species range in Pennsylvania, was likely important to the rate of range expansion of bears in Pennsylvania.