Dispersal patterns and distance movements of subadult American black bears in Virginia

1
Dispersal patterns and distance movements of
subadult American black bears in Virginia

• Daniel J. Lee
• Michael R. Vaughan
• Department of Fisheries and Wildlife Sciences
• Virginia Polytechnic Institute and State
  University

2
Introduction

• Dispersal importance
• Population establishment and maintenance
• Genetic variability among bear populations
• Survival consequences
• Few studies
• Collaring of fast growing subadults
• Recapture and tracking dispersing bears
• Most studies focus on adult females

3
What is dispersal?

• No universal definition for all animals or bears
• Essence is a one way movement without return
• Past bear research definitions
• Leaving the adult females home range to
  nonadjacent area (Rogers 1977)
• Moving gt 20 km (Alt 1978)

4
What is dispersal?

• Defined so that bears would not overlap with
  mothers home range over time
• Males
• gt 20 km based on radius of adult female
  diameter of adult male
• Females
• Home range overlap of adult and subadult females
• gt 8 km based on radius of adult female diameter
  of adult female

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Objectives

• 1.Determine if subadult male and subadult female
  black bears exhibit dispersal behavior.
• 2. Determine if dispersal distance differed by
  sex.
• 3. Determine if bears disperse in a random
  direction.
• 4. Examine the relationship between dispersal
  distance and survival.

6
Study areas
7
General Methods

• Trapping and den work 1999 2001

8
General Methods

• Use of eartag
• transmitters

9
Analysis Methods

• Subadults ? 3 years old
• Separated data
• residents born on study area to known adult
  female
• summer captures birth place and mother unknown
• Initial and final locations
• yearling den / capture site
• drop site, harvest site, 2002 den site

10
Analysis Methods

• Fishers exact test - dispersal behavior by sex
• ?2 distance intervals (5 km) moved for
  residents by sex
• Rayleigh tests - direction of movement
• ?2 for trends trend in fate for males by
  distance traveled
• ? 0.05

11
Results

• Attached transmitters to 31 residents (11M20F)
  and 70 summer captures (44M26F)
• Age
• 1 2 3
  Multiple years
• Residents M 11 0 0
  0
• F 14 6 0
  8
• Summers M 21 18 5
  2
• F 5 12
  9 8

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Results Discussion
Obj. 1. Behavioral differences in dispersal

• Dispersed Did not disperse
• Female 0 20
• Male 3 8
• Fishers exact 6.039 P 0.04

Residents
13
Results Discussion
Obj. 1. Behavioral differences in dispersal

• If dispersal movement out of moms home range,
  then 9 of 11 males dispersed
• Summer captures may already have dispersed before
  capture
• Supports findings of Rogers, Alt, Schwartz and
  Franzmann, and others

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Results Discussion
Obj. 2. Distance moved

• ?2 8.54 P 0.01

15
Results Discussion
Obj. 2. Distance moved

• ?2 22.02 P lt 0.001

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Results Discussion
Obj. 2. Distance moved
Males

• Age Group n Mean SE Range
• 1 Residents 11 15.7 2.2 1.8 - 63.6
• Summers 21 14.7 4.1 0.9 - 80.0
• 2 Residents 0 --- --- ---
• Summers 19 12.2 3.2 1.9 - 61.4
• 3 Residents 0 --- --- ---
• Summers 6 11.6 3.2 2.5 - 23.9

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Results Discussion
Obj. 2. Distance moved

• No females moved gt10 km
• Greatest male dispersal 63.6 and 80 km
• 20 of subadult males moved gt 20km
• similar to movements in Pennsylvania (max
  dispersal 53 km) and Tennessee (66 km)
• No yearlings returned after dispersing

18
Results Discussion
Obj. 3. Direction of movement

• Rayleigh test r P
• Resident males 0.094 0.90
• Summer capture males 0.184 0.24
• All males gt 20 km 0.596 0.02
• All males gt 15 km 0.513 0.02

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Results Discussion
Obj. 3. Direction of movement
N

• All males gt 15 km
• Using ridge lines to disperse
• Avoidance of Interstate 81 and developed lands?

20
Results Discussion
Obj. 4. Relationship between survival and
distance
Percent of residents for each fate by distance

• 0-5 km 5-10
  km 10 km
• Fate M (5) F (16) M (2) F (4)
  M (4) F (0)
• Alive 20 56 50
  50 0 0
• Unknown 40 31 0
  50 50 0
• Dead 40 13 50
  0 50 0
• ?2 0.09 P 0.77

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Results Discussion
Obj. 4. Relationship between survival and distance
Percentage of summer captures for each fate by
distance

• 0-5 km
  5-10 km 10 km
• Fate M (14) F (23) M (15) F (3)
  M (15) F (0)
• Alive 50 56 34
  63 20 0
• Unknown 7 30 13
  33 13 0
• Dead 43 13 53
  0 67 0
• ?2 1.62 P 0.20

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Conclusions

• Males dispersed, females did not
• Yearling and two-year-old age classes moved
  greatest distances
• Direction of dispersal was not random and may
  favor landscape features
• Moving greater distances may increase mortality
  risk

23
Management Implications

• Female movement into new areas slow
• Translocation of females necessary for
  establishment across barriers or in
  over-harvested areas

24
Acknowledgements

• Virginia Polytechnic Institute and State
  University
• Virginia Department of Game and Inland Fisheries
• USGS - BRD
• USFS
• Virginia Bear Hunters Association

25
Thanks

• Questions?