Population characteristics of grizzly bears in the Arctic National Wildlife Refuge, Alaska

1
Population characteristics of grizzly bears in
the Arctic National Wildlife Refuge, Alaska

• Harry V. Reynolds, III
• Patricia E. Reynolds
• Donald D. Young
• Gerald W. Garner

2
Study objectives

• Describe population characteristics using
  measures of reproduction and survival
• Use these parameters in a model to predict rates
  of population growth and yield

3
Study area in the Arctic National Wildlife
Refuge, Alaska
4
Methods

• Used capture records and radio-relocation data
  from 211 marked female grizzly bears and 155
  unmarked offspring
• Data were collected from 1982-1994 in
  northeastern Alaska

5
Reproductive histories of 95 marked
female grizzly bears
Mean age at first parturition
Mean age at last parturition
Maximum life span
6
Mean inter-birth interval Mean litter size Sex
ratio
7
Mean annual reproductive rate female cubs per
female per year
8
Age specific survival Survival to age at first
parturition Annual adult survival
9
Population model to predict rate of growth and
yield
Information needed Pa survival to first
parturition P annual adult survival a age
at first reproduction F mean annual
reproductive rate w maximum age litter size
mean number of cubs per litter interval mean
interval between births N population size
set at 100
10
Results
11
Age at first parturition
12
Number of female grizzly bears first reproducing
at each age
13
Reproduction at old age
14
Sex ratio of grizzly bear cubs ( N 40)
15
Interval between consecutive litters of grizzly
bear cubs
16
Inter-birth intervals observed in female grizzly
bears (N 58)
17
Size of cub litters with marked female grizzly
bears
18
Frequency of cub litter size (N 94)
19
Grizzly bear survival rates Survival to age 1
44 Survival to age at first parturition
18 Adult annual survival 98
20
Values of parameters used in population model
21
Estimates from model
22
Conclusions
Survival rates, especially of cubs was very
low. Once females reach adult age, survival was
very high. Low productivity was not unexpected
since these bears live at the limit of their
range Speculation reproductive strategy drives
females to access habitat with high availability
of caribou, but also higher vulnerability to
mortality of offspring.