Pre and PostNatal Cub Development in American Black Bears

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Pre- and Post-Natal Cub Development in American
Black Bears

• Colleen Olfenbuttel
• Dr. Mike Vaughan
• Cooperative Alleghany Bear Study
• Department of Fisheries and Wildlife
• Virginia Tech
• Blacksburg, VA U.S.A.

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Funding provided by

• Virginia Department of Game and Inland Fisheries
• U. S. Forest Service
• Virginia Tech
• USGS-Biological Resources Division

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The Center for Ursid Research

• Purpose
• To further the understanding of the reproductive
  biology of female American black bears
• Mechanisms for implantation
• Implantation dates
• Fetal cub development
• Post-natal cub development
• Pre- and post-natal mortality

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The Center for Ursid Research-Background

• Started in Fall 1987
• 1 of only 2 university facilities in North
  America to temporarily hold and perform research
  on American Black Bears
• Holds up to 6 black bears
• Nuisance female black bears
• Held from early August through mid-May

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Methods Monitoring Adult Condition

• Sampling occurs every 10 days
• October 1st through April 29th
• Bears immobilized
• 21 mixture of ketamine and xylazine
• Each sampling period
• Adult blood drawn
• Adult weight recorded
• Ultrasound performed December through February

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MethodsMonitoring fetal cub development

• Ultrasonography performed December through
  February
• Performed by Virginia Tech School of Veterinary
  Science
• Ultrasonography documents
• Detection of amnionic vesicle
• Pre-natal cub development
• measure crown-rump growth
• cubs present
• Cub resorbtion
• Cub heartrate

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Black bear fetus
Cub heartrate
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Head
Rump
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MethodsMonitoring post-natal development

• The Center documents
• Date of birth
• Cub mortality
• Morphological measurements every 10 days
• Age when eyes open
• Age when teeth erupt

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5 days
25 days
45 days 65 days 75 days
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Preliminary Results

• Since 1987
• Held 77 female black bears
• 105 cubs born
• Fostered 45 cubs to mothers
• 100 acceptance rate
• Documentation of pre- and post-natal mortality

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Adult female parameters

• Parameter Mean Range
• Age (years) 7 2 19
• Fall weight change () 25.7
  -12 60
• Winter weight loss () 28 20
  38
• Weight at parturition (kg) 86.7
  65.3 115.2
• Litter size 2.37 1 3
• Litter sex ratio 11
• Fetal detection date Jan. 4 Dec.
  20 Jan. 20
• Birth after detection (days) 32.1 4 47
  

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Research GoalsAdult Females

• Weight change during
• Hyperphagia
• Hibernation
• Factors affecting
• Reproductive success
• Litter size
• Parturition date

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Pre- and Post-Natal Mortality

• Poorly documented due to inability to closely
  monitor hibernating American black bears
• Leads to erroneous conclusions regarding
• Fetal development
• Female fertility
• Cub survivorship

• Pre-natal detection
• Ultrasonography
• Vaginal discharge

• Post-natal detection
• Absence of cubs
• Presence of scat

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Pre-natal mortality
Amnionic vesicle resorbing into uterine wall
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Post-natal mortality
Claws from 3 cubs recovered from mothers scat
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Pre- and Post-natal Mortality Parameters
Parameter N Pre-natal (n123 cubs
detected) Resorbed 7 In Utero
(unknown) 9 Aborted 2 Total
18 (14.6) Post-Natal (n105 cubs
born) Mortality 37 (35) Mean
birth date February 4 Mean age at death
6 days
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Preliminary Results Mothers Diet and Cubs

• Mean Mean
• Mothers Diet cubs detected Age of
  Death
• Normal (2000g/day) 2.36 6 d
• Early (2000g/day) 2.27 5 d
• Low  (1000g/day) 1.63 1.5 d

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Preliminary ResultsMothers Diet and Cub
mortality
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Research GoalsPre- and post-natal mortality

• Frequency of partial and whole litter loss
• Factors behind mortality
• Litter size
• Sex of cub
• Mothers condition
• Age
• Weight
• Weight change during fall and winter
• Benefits
• More accurate assessment of female fertility and
  cub survivorship

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Research GoalsCub Growth Rates

• Factors affecting growth
• Mothers condition
• Date of birth
• Litter size
• Sex of cub
• Sex ratio
• Fostered cubs

Increased understanding of - Factors
influencing cub growth rates - Consequences of
fostering on natural cub growth
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Questions?