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Effects of hunting on brown bear cub survival and litter size in Alaska

January 2003
Ursus 14(2):130-152

Authors:

Sterling D. Miller

Dunrovin Research in Lolo Montana

Jeff Keay

United States Geological Survey

We present data from 4 studies of radiomarked brown bears (Ursus arctos) in Alaska to evaluate the effects of hunting and differential removal of males on cub survival and litter size. In the Susitna area in southcentral Alaska, the proportion of males declined during a period of increasing hunting pressure (1980-96). Cub survivorship was higher in the heavily hunted Susitna population (0.67, n = 167 cubs) than in a nearby unhunted population in Denali National Park (0.34, n = 88 cubs). On the Alaska Peninsula, in coastal areas rich in salmon (Oncorhyncliits spp.) and with higher brown bear densities, cub survivorship was significantly higher in the hunted Black Lake population (0.57, n - 107 cubs) than in an unhunted population in Katmai National Park (0.34, n = 99 cubs). The Black Lake population had alternate-year hunting, and cub survivorship was similar during years with and without hunting during the preceding fall and spring. In both coastal and interior comparisons, litter sizes were either larger or not significantly different in hunted areas than in nearby unhunted national parks. We found no evidence that removal of adult male bears by hunters reduced cub survival or litter size. For populations below carrying capacity, convincing evidence is lacking for density dependent effects on cub survivorship or litter size. In our studies, variations in cub survivorship and litter size were best explained by proximity to carrying capacity; local environmental factors and stochastic events probably also influence these parameters. We believe that cub survivorship in our national park study areas was lower than in nearby hunted areas because of density-dependent responses to proximity to carrying capacity.

Trends in brown bear harvests in south-central Management Subunit 13E, 1965-97.

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Effects of hunting on brown bear cub survival

and litter

size in Alaska

Sterling D. Miller1'4, Richard A. Sellers2, and Jeffrey A. Keay3'5

1Alaska

Department

of Fish and Game, 333 Raspberry

Road, Anchorage,

99518-1599, USA

2Alaska

Department

of Fish and Game, P.O. Box 37, King

Salmon,

99613-0037, USA

3U.S. Geological Survey,

Alaska Biological

Science Center,

1011 East Tudor

Road,

Anchorage,

99503, USA

Abstract: We present

data from 4 studies of radiomarked

brown bears (Ursus arctos) in Alaska to

evaluate

the effects of hunting

and differential removal of males on cub survival

and litter size. In the

Susitna area in southcentral

Alaska, the proportion

of males declined during

a period of increasing

hunting pressure

(1980-96). Cub survivorship

was higher in the heavily hunted Susitna

population

(0.67, n = 167 cubs) than

in a nearby

unhunted

population

in Denali National

Park

(0.34, n = 88 cubs).

On the Alaska Peninsula,

in coastal areas

rich in salmon

(Oncorhynchus

spp.) and with higher

brown

bear

densities,

cub survivorship

was significantly

higher

in the hunted Black Lake

population

(0.57, n

= 107 cubs) than

in an unhunted

population

in Katmai National

Park

(0.34, n = 99 cubs). The Black

Lake population

had alternate-year

hunting,

and cub survivorship

was similar

during years with and

without

hunting

during

the preceding

fall and spring.

In both coastal and interior

comparisons,

litter

sizes were either

larger

or not significantly

different

in hunted

areas

than

in nearby

unhunted

national

parks.

We found

no evidence that removal

of adult

male bears

by hunters

reduced

cub survival

or litter

size. For populations

below carrying

capacity,

convincing evidence is lacking for density dependent

effects on cub survivorship

or litter

size. In our studies, variations

in cub survivorship

and litter

size

were best explained by proximity to carrying

capacity; local environmental

factors and stochastic

events probably

also influence

these parameters.

We believe that

cub survivorship

in our

national

park

study areas was lower than in nearby hunted areas because of density-dependent

responses to

proximity

to carrying

capacity.

Key words: Alaska, brown bear,

compensatory

mechanisms,

density dependence,

grizzly bear,

hunting,

infanticide,

intraspecific

mortality,

sexually selected infanticide,

survivorship,

Ursus arctos

Ursus 14(2):130-152 (2003)

Brown bears

are

characterized

by low rates

of natural

mortality

in adult

age classes and

higher

rates

of natural

mortality in newbors and subadults. In a review of

North

American

brown

bear

studies,

cub (defined

here

bears

in the first

year

of life) mortality

rates

were

30-40%

(Bunnell and Tait 1985). Demographic models and

calculated

levels of sustainable

harvest

will be influenced

4Present

address:

National

Wildlife

Federation,

240 North

Higgins,

Suite

2, Missoula,

59802,

USA,

email:

millerS@

nwf.org

5Present

address:

Florida

Integrated

Science

Center,

412 NE

16th Avenue,

Room 250, Gainesville,

Florida

32601-3701

USA,

jeff_keay@usgs.gov

by factors that affect survival of cubs. However, few

data are

available

on causes

of cub

mortality

on factors

that may influence

recruitment

rates. In the absence of

such data,

there

has been considerable

speculation

about

relationships

between adult bear abundance

(especially

adult

males) and cub survivorship.

An inverse relationship

between abundance

of adult

males and survivorship

of cub and older dependent

offspring was suggested by McCullough (1981) and

Stringham (1980, 1983) based on data collected by

Craighead

et al. (1974) in Yellowstone National Park.

The basis for this reported

compensatory

relationship

was the suspicion that because male bears kill cubs,

reductions in male abundance would increase cub

survivorship.

These interpretations

of Craighead data

130

HUNTING

EFFECTS ON CUB SURVIVORSHIP

* Miller et al. 131

were challenged by Craighead

et al. (1995) as well as

McLellan (1994).

Most human hunting of bears is biased toward

males for a variety of reasons (Bunnell and Tait 1981,

1985; Miller 1990a; McLellan 1994; Derocher et al.

1997). Based on the suggestions

of McCullough

(1981),

a positive (compensatory) relationship

between hunt-

ing and cub survivorship

has been accepted by some

managers

of exploited

bear

populations.

This was explic-

itly identified as a benefit of brown bear hunting in

Montana

by Dood et al. (1986). An early draft of the

environmental

impact statement for black bear hunt-

ing in California

asserted,

"The number of bears killed

is expected to be replaced by increased survival of

young," and included this relationship

in a demographic

model used to justify hunting bears (California Fish

and Game 1999:64). This relationship was omitted

from a revised version of the model (R. Barrett, 2000,

The black bear population model-additive mortality,

version 4-15-2000, University of California, Berkley,

California,

USA).

Recent reviews found no evidence indicating in-

creased cub survivorship

resulted from reduced abun-

dance of male bears

for North American

populations

brown bears (McLellan 1994), black bears (U. ameri-

canus; Ruff 1982, Garshelis 1994, Sargeant

and Ruff

2001), and polar bears (U. maritimus;

Derocher and

Taylor 1994). Miller (1990b) and Taylor

(1994) recom-

mended

that until studies adequately

demonstrated such

a relationship,

managers

should not include it in bear

population

or harvest models.

Studies in Scandinavia

reported

the opposite conse-

quence of male biased hunting.

These studies reported

that selective removal of males decreased brown bear

cub and yearling survivorship

(Swenson et al. 1997;

2001a,b; Swenson 2003). These authors concluded

that removing a male bear caused social disruptions

that resulted in lower cub survivorship

0.5-1.5 years

following male removal in the fall. This conclusion

was based on (1) observed

differences

in cub survivor-

ship between 2 areas with different rates of male re-

moval, (2) rejection

of alternative

explanations

for the

differences

and (3) male removal experiments

reported

by Swenson (2003). The Scandinavian authors con-

cluded that the differences in cub survivorship

were

caused by sexually-selected infanticide (SSI) as has

been observed in lions (Panthera leo), primates, and

other species (Hrdy 1979, Hrdy and Hausfater 1984,

Janson and van Schaik 2000, Van Noordwijk and van

Schaik 2000). Sexually-selected infanticide can be

advantageous

to males who kill offspring fathered

other males, breed with the mother, and father

additional offspring. New findings in Scandinavia

clarified that the SSI reported for the Scandinavian

studies resulted primarily from increased predation

by resident adult males and not from immigrant

subadult males subsequent

to the death of a resident

male (Bellemain et al. reported

in Swenson 2003). In

Scandinavia, increased mortality of yearling females

(but not yearling males) was also reported

2.5 years

following the death of a resident male. This was

attributed to intraspecific predation rather than SSI

(Swenson et al. 2001a).

In southern

Alberta, Canada, Wielgus and Bunnell

(1994a,b; 1995; 2000) concluded that a small brown

bear population at Kananaskis

was destabilized when

adult males were killed by hunters and replaced by

immigrant

subadult

males (presumed

to be more prone

to infanticide). These subadult

males were concluded

to have displaced adult females from good foraging

habitats, thereby compromising the females' physical

condition and causing smaller litters. Wielgus and

Bunnell (2000) also concluded that bears from an un-

hunted

population

in the Selkirk

Mountains

of northern

Idaho and southern British Columbia

had larger litters

than the Kananaskis

population.

They reported

that the

unhunted Selkirk bears had higher survivorship of

resident

adult males, less immigration

of young males,

and less avoidance of prime foraging areas by adult

females. All this resulted

in better

female condition

and

larger litter sizes compared

to the hunted Kananaskis

population (Wielgus and Bunnell 2000). This conclu-

sion was used as the basis for a demographic

model

suggesting

that, "... the effects of adult

male mortality:

increased immigration by new males, related sexual

segregation,

and reduced

reproduction

... can result in

lowered

population

growth

and population

declines and

can even lead to rapid population extinctions when

numbers are very small" (Wielgus et al. 2001:299).

In contrast to SSI arguments, Craighead et al.

(1995:99) wrote that "[we view] infanticide in grizzly

bears as an expression

of a foraging

strategy

(conspecific

predation) ... rather than as a genetically acquired

mating strategy practiced by a subset of [socially

dominant

adult

males]."

Authors of the studies in Canada and Scandinavia

suggested their conclusions have management

implica-

tions. Swenson et al. (2001b)

and

Swenson

(2003) recom-

mended

that

managers

assume

that

loss of adult

males has

a depensatory

relationship

on cub survivorship;

they

estimated that male removal in their Scandinavian

study area

reduced

the population

growth

rate

by 4.5%.

Ursus 14(2):130-152 (2003)

132 HUNTING EFFECTS ON

CUB SURVIVORSHIP

* Miller et al.

Wielgus and Bunnell (2000:153) concluded "[our]

studies do suggest that the commonly accepted

hypothesis that increased reproduction derives from

trophy hunting could contribute to further

declines in

some grizzly bear

populations."

Janson and van Schaik

(2000) and Boyce et al. (1999) cited Swenson et al.

(1997) as an illustration that increased infanticide

might be a consequence of male based hunting in

mammal

populations. Boyce et al. (2001) cited studies

in Scandinavia (Swenson et al. 1997) and southern

Canada

(Wielgus 1993) as illustrating possible relation-

ships meriting

consideration in managing

bear hunting.

In contrast,

a panel of 6 scientists reviewed brown bear

hunting management in British Columbia and con-

cluded: "that

presently available data on [effects of se-

lective removal of males by hunting] are equivocal,

and therefore hunting-related changes in density or

social structure should not be incorporated

into [British

Columbia]

harvest

management"

(J. Peek, J. Beecham,

D. Garshelis,

F. Messier, S. Miller, and D. Strickland,

2003, Management of grizzly bears in British

Columbia: A review by an independent scientific

panel, Minister of Water, Land and Air Protection,

Government of British Columbia, Victoria, British

Columbia, Canada,

page 53).

We examined data from Alaska for evidence of

relationships between brown bear hunting biased to-

ward males and cub survival and litter size. We report

temporal comparisons in a population in southcentral

Alaska exposed to increasing hunting

pressure designed

to reduce brown bear predation

on moose (Alces alces)

calves over a 16-year period.

We compare

cub survivor-

ship and cub litter sizes in hunted and unhunted

popula-

tions in southcentral Alaska. We also compare high-

density

hunted and

unhunted

populations

in salmon-rich

habitats on the Alaska Peninsula and cub survivorship

following years with and without

hunting

on the Alaska

Peninsula.

Study areas

Southcentral Alaska

Upper and Middle Susitna. Temporal changes

in population density and composition in southcentral

Alaska were measured

in the 1,325 km2 Middle Susitna

study area

(MidSu) during 1985 and 1995 (Miller et al.

1987, Miller 1990c; Fig. 1). MidSu was characterized

forests of spruce (Picea glauca and P. mariana), birch

(Betula papyrifera), and alder (Alnus spp.) at lower

elevations along the Susitna River. Above approxi-

mately 800 m elevation the vegetation graded

into shrub

Fig. 1. Location of Alaskan study areas for un-

hunted (Denali and Katmai) and hunted (MidSu,

UpSu, and Black Lake) populations of brown bears,

1980-1997.

tundra and then into mat and cushion tundra.

In MidSu,

only one stream

(Prairie Creek) in the southwest comer

had a run of salmon (Oncorhynchus tschawytscha);

this

run was exploited in July by a small proportion

of the

radiomarked bears in MidSu (Miller 1987).

Access to MidSu by bear, moose, and caribou

(Rangifer tarandus) hunters was by aircraft, snow

machines, or all-terrain

vehicles, depending on season.

MidSu was in a relatively remote portion of Alaska's

Game Management Unit (GMU) 13, Subunit 13E

(17,555 km2, Fig 2), bordered

on the north

by the crest

of the Alaska Range and on the south by the Talkeetna

Mountains. Denali National Park overlapped

the north-

western corer of Subunit 13E.

We also used reproductive and survival data from

radiomarked bears in the Upper Susitna study area

(UpSu) 40 km northeast of MidSu. Most of the UpSu

was in Game Management Subunit 13E, but a small

portion was in Subunit 13B (Fig. 2). UpSu surrounded

the headwaters of the Susitna River, bordered on the

east by the Clearwater

Mountains and on the north by

the crest of the Alaska Range. Bears in UpSu had no

access to salmon, but moose density and vegetation

were otherwise comparable to MidSu (Miller 1990c,

Ballard et al. 1991). Moose densities in UpSu were

688-848/1,000 km2

during

1980-83 (Miller

and Ballard

1992). Hunting regulations

were the same in UpSu and

MidSu. UpSu was adjacent

to the Denali Highway (Fig.

2) and was more easily accessed by bear hunters.

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS ON

CUB SURVIVORSHIP

* Miller et al. 133

Although both UpSu and MidSu were

heavily hunted for brown bears, bear

hunting

was earlier

and more intense in

UpSu because of easier hunter access

(Miller and Ballard 1992). By 1987,

UpSu had a reduced

density of brown

bears and a population

skewed in favor 1"

of females (Miller 1990c). Black bears

were rare

in UpSu but were common

MidSu in forested habitats along the

Susitna River.

Hereafter,

data collected

in MidSu and UpSu areas are referred

to as Susitna data. ? kilometers

Brown bear hunting regulations

were liberalized

by the Alaska Board

of Game to increase brown bear har-

vests during 1980-2003 throughout

GMU 13. The motive for these liber-

alizations was to reduce brown bear ab-

undance and bear predation

on moose

(Miller and Ballard 1992). A spring

season for brown bears was initiated in

1980. In 1979, brown

bear

hunting

was Fig. 2. Alask.

open 1 September-10

October,

the bag where a hunte

limit was 1 per 4 years, and residents 9f A portiot

needed a $25 brown bear tag. By the for 2 study ar

end of our study in 1997, the season

was open 10 August-31 May, the bag

limit was 1 per year, and no tag was required

for Alaska

residents. The August season was authorized in 1995 to

encourage caribou hunters to take bears incidental to

caribou hunts. In 2003, the hunting season for brown

bears was expanded

to 365 days.

Denali National Park. We compared

our data from

Susitna studies to data collected in Denali National Park

(hereafter "Denali", Keay 2001 and J. Keay unpub-

lished data). Denali overlaps the northwestern

portion

of Subunit 13E (Fig.l), but Keay's study area was in

Subunit 20C on the opposite (north)

side of the Alaska

Range. The Denali study area included a similar mix

of bear foods and habitat types, although typically at

higher elevations (600-2,000 m) and with fewer trees

than in Susitna. Moose densities in Keay's study area

were much lower (60/1,000 km2 at elevations below

1,050 m, Adams et al. 1995) than in Susitna

(600-1,000

moose/1,000 km2, Miller and Ballard 1992). Like

bears in the UpSu area and most bears in the MidSu

area, bears in the Denali study area had no access to

salmon.

There were no documented

human-caused mortalities

to brown bears in the Denali population. Keay (2001)

a's Game Management Unit 13 in Southcentral Alaska,

d population of brown bears was studied during 1980-

Af Denali National Park

overlaps the northwestern border

E. Population composition and density were estimated

aas in Subunit 13E (MidSu and UpSu).

found no evidence of poaching within the study area,

and there were no management

kills or translocations of

nuisance bears. Keay (2001:4) concluded that "human

activities have had virtually no impact on grizzly bear

population dynamics in the study area for at least 80

years." Thus, the comparisons

of demographic param-

eters between Susitna and Denali represent compari-

sons between a population that has long been hunted,

especially in the 1990s, and an unhunted population.

Habitat comparisons. Habitats were not identical

in Denali and our Susitna study areas, but these areas

shared the same primary

sources of nutrition

available

to bears. Stable isotope analyses based on hair sam-

ples from the Susitna area and Denali study areas were

conducted by Hilderbrand et al. (1999; samples for

Susitna were provided by S.D. Miller and came from

MidSu). Marine meat (salmon) constituted none of the

diet in Denali compared to 4% (+6%) in Susitna.

Terrestrial meat constituted 4% (+11%) in Denali Park

compared to 9% (_+13%) in Susitna. Plant matter

constituted 96% (+ 11%) of the brown bear diet in

Denali and 87% (_+13%) in Susitna. Overall, both

Denali and Susitna populations consumed among the

Ursus 14(2):130-152 (2003)

134 HUNTING

EFFECTS ON CUB

SURVIVORSHIP

* Miller et al.

lowest proportions

of dietary meat among the brown

bear

populations

studied

by Hildebrand

et al. (1999).

Alaska Peninsula studies

Black Lake. The Black Lake study area was on

the Alaska Peninsula 360 km southwest from Katmai

(Fig. 1). Most bears were captured

within a 1,215 km2

area where we estimated bear density (Miller et al.

1997). The Black Lake study area

was bordered on the

southeast

by the Pacific Ocean and on the northwest

Bristol Bay; it had a subarctic-maritime

climate and

vegetation pattern

similar to that in the Katmai study

area. All five species of Pacific salmon were found

within the Black Lake area, but sockeye salmon (O.

nerka) in the Chignik River provided

the most reliable

food source for bears.

The Black Lake study occurred in Subunit 9E

(31,000 km2), which was the most popular

brown bear

hunting area in Alaska in which hunter participation

was not limited by permits. There were no roads

connecting the Alaska Peninsula with the rest of

Alaska, but access by small aircraft

was relatively

easy

for hunters. Subunit 9E was popular for brown bear

hunting by both guided nonresident and unguided

Alaska resident

hunters.

Unlike Susitna,

hunting regulations

in the Black Lake

study area were designed to maintain sustainable

harvests and a population with large (trophy) males.

Excessive harvests and reduced densities during the

late 1960s and early 1970s prompted

studies at Black

Lake (Glenn 1980, Glenn and Miller 1980). Subse-

quently, bear populations on the Alaska Peninsula

including Subunit 9E increased

in response to conser-

vative management based on alternate year hunting

seasons (Sellers 1994, 1998). Counts of bears along

salmon streams indicated that bear numbers have

increased in recent decades (Sellers 1998 and un-

published

data).

Katmai National Park. The Katmai

National

Park

(hereafter Katmai) brown bear study (Fig. 1) was

initiated

shortly

after

the March 1989 Exxon Valdez

oil

spill to assess damage

to bear

populations.

Brown bears

were captured

and

radiomarked

on the central

portion

the Shelikof Strait

coast of Katmai.

The primary

study

area

was bordered

by Shelikof Strait

on the east and the

crest of the Aleutian Mountains (to 2,318 m) on the

west. Brown bear density was estimated

within a 901-

km2 area (Miller et al. 1997). Trees were sparse

in the

study

area.

Below the zone of alpine

tundra,

alder

(Alnus

crispa) and willow (Salix spp.) were abundant.

Salmon

(primarily

pink [0. gorbuscha], chum [0. keta], and

coho [0. kisutch])

spawned

in numerous streams distrib-

uted throughout

the study area. Additional vegetative

information was provided by Cahalane (1959). No

influences from Exxon Valdez oil pollution on bear

survival or reproduction

were detected. Survival was

0.36 for cubs (n = 26) of females using polluted areas

and 0.37 for cubs (n = 37) of females using unpolluted

areas (X2

= 0.03, 1 df, P = 0.86, Sellers and Miller

1999).

The Katmai

study

area

was located

centrally

in an area

closed to bear

hunting

since 1931. Subsequent

additions

to the park

in 1942, 1969, and 1980 expanded

the area

closed to hunting.

Additional

closures during 1985-96

north

of Katmai

resulted

in expanding

the area

closed to

bear hunting

to 14,500 km2. Prior to the Exxon Valdez

oil spill, human presence was limited primarily to

commercial

fishers

and occasional

guided sport

anglers.

There were no documented

human-caused

mortalities

Katmai

since 1985, although

2 bears

marked

in Katmai

were later shot outside park

boundaries.

Habitat comparisons. Dietary composition of

bears in Black Lake and Katmai

study areas was anal-

yzed by Hildebrand

et al. (1999) using stable isotope

analysis

based

on samples

provided

by R. Sellers.

Marine

meat (primarily

salmon)

constituted

79% (+ 14%)

of the

diet at Black Lake

compared

to 62% (+25%) at Katmai.

Plant matter and terrestrial

meat, respectively, repre-

sented 19%

(+ 11%)

and 2% (+5%) of the bears'

diet at

Black Lake compared

to 31% (? 19%)

and 7% (+15%)

at Katmai.

Compared

to the Denali and

GMU 13 studies,

bears on the Alaska Peninsula ate >15 times more

salmon. Miller et al. (1997), Hilderbrand

et al. (1999),

and others correlated

the abundance

of salmon with

higher

densities

and larger

body sizes in Alaskan

brown

bears.

Black bears did not occur in either of the Alaska

Peninsula

study areas.

Methods

One objective of the studies on the Alaska Peninsula

and in GMU 13 was to examine

the influence

of harvest

on survivorship

of juvenile

brown

bears.

In all areas

data

were obtained by periodically locating radiomarked

bears and observing litter size. Density estimates were

derived from capture-mark-resight

estimates obtained

using radiomarked

individuals to establish geographic

closure (Miller

et al. 1997). We defined

cubs as bears

their first year of life and yearlings as bears in their

second year of life. Subadults

were bears <5 years old

no longer

with

their

mother.

Throughout

most of Alaska,

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS ON CUB SURVIVORSHIP

* Miller et al. 135

including

our

study

areas,

brown

bears

typically

separate

from their

mothers

in the spring

of their 3rd

year of life

(at age 2), infrequently

in their

4th year of life or older,

and rarely

as yearlings (Sellers and Miller 1991, Miller

1993a).

During 1980-95, we captured and marked 175

different brown bears in Susitna (Miller 1997a). Dur-

ing 1988-94 we captured 112 different

individuals in

Black Lake, and during 1989-1993 we captured

122 in

Katmai. During 1991-1998, we captured

74 different

individuals in Denali. Bears were captured

following

searches with fixed-wing aircraft.

Bears were darted

from a helicopter

(Miller et al. 1997) in and near areas

used for density estimation.

In all study areas, all cap-

tured adult females were fitted with radio transmitters.

Where

feasible, adult males and subadults of both sexes

were also fitted with radio transmitters

equipped with

drop-off features.

We periodically

replaced

radio trans-

mitters on bears by recapturing

them (up to 7 times

during

the 16 years, Miller 1997a, b).

Harvest data and hunter selectivity

Harvest data. Inspection

was required

of hides and

skulls of bears shot by hunters in Alaska.

During

inspec-

tion, officials determined

sex, recorded the location of

kill, and extracted a premolar

for aging by counting of

cementum annuli (Matson et al. 1993). Evidence of

gender,

based on hide examination,

was inconclusive in

<2% of bears examined, and in such cases bears were

allocated to a "sex unknown"

category.

Hunter selectivity for males. Hunting provided

an opportunity

to test for responses

to reduction in male

abundance in bear

populations

because

hunters

bias kills

toward males. In Alaska, this was a consequence of

hunting regulations as well as bear behavior. Male

bears were especially vulnerable to hunters during

spring seasons because they exited their dens early

when hunting

conditions

were more favorable than

later

during

the spring

(Miller 1990d, Van Daele et al. 1990).

Male bears are also especially vulnerable

during

spring

seasons because seasons for other species are not open

and hunters

afield are bear hunters

mostly interested in

larger (trophy) bears. In all seasons, male are more

vulnerable

than females because they have larger

home

ranges, which increases the likelihood that they will

encounter hunters. Subadult males, unlike subadult

females, emigrate from their maternal home ranges

(Pasitschniak-Arts

and Messier 2000, Schwartz et al.

2003). This movement of subadult

males also increases

the likelihood they will encounter

hunters.

In Alaska,

regulations

prohibited

shooting

females accompanied

cub or yearling offspring. We believe this regulation

additionally protected

many females accompanied

by 2-

year old offspring

during

spring seasons because many

hunters were unwilling to shoot females accompanied

by offspring of any age. This further

contributed

hunter selectivity for males during spring. The reg-

ulation protecting females accompanied by cub and

yearling offspring functionally

protected

adult females

from

hunter

harvests

during

approximately

83%

of open

hunting

periods;

such females were typically

vulnerable

only during

autumn

following weaning of their 2 year-

olds (assuming a new litter was born the following

spring).

Harvest rates and kill density

We estimated

harvest

rates as: (1) the proportion

marked

bears

killed by hunters

and (2) reported

kills in

a subunit

divided by the estimated

population

of bears

in the portion of the subunit open to hunting. Popu-

lation sizes were estimated by stratified

extrapolation

from density estimation

areas

(Miller

et al. 1997) to the

surrounding

area. In southcentral

Alaska, we developed

upper and lower bounds for estimated

harvest rate by

making conservative and liberal assumptions about

whether

marked

bears that disappeared

during

hunting

season but were not reported

in the harvest had been

killed. Only bears

>2 years

old were included in harvest

rate calculations.

In Katmai

and Black Lake, we estimated

the cumu-

lative number

of marked

bears available

for harvest in

each of 4 categories (adult males, adult females,

subadult males, and subadult females) by applying

annual survival

rates to the number

of bears originally

marked. The harvest rate was calculated by dividing

the cumulative number of marked-bear

years into the

number of marked bears killed by hunters through

1996.

Kill density was defined as the number of bears

reported

killed per 1,000 km2. Kill density for male

bears >5 years old was calculated

based on the harvest

data

and the entire

area in the harvest

management

area

(Game Management Subunit). Surface area was not

corrected for areas

of unacceptable

bear

habitat

such as

high elevations or lakes, so kill density based on

occupied bear habitat would be slightly higher than

values we report

here.

Population composition

Standard

techniques for measuring

population

com-

position in bears are not available. All available tech-

niques,

short

of a complete census, have biases. Because

Ursus 14(2):130-152 (2003)

136 HUNING EFFECTS ON

CUB

SURVIVORSHIP

* Miller et al.

male bears have larger home ranges and greater

daily

movements than

females, and because most methods of

measuring composition are based on knowledge of

which bears were present in an area during a period,

male abundance

will be overestimated relative

to female

abundance.

We used 3 approaches to estimate population

composition.

For the first

estimate,

we inferred

compo-

sition from the sex and age composition of harvested

bears. A predominance of males in the harvest of

a heavily hunted bear population should reduce the

proportion

of living males compared

to a less exploited

population

(Fraser

et al. 1982). This should

be especially

notable

in older

cohorts.

Harvest data

were examined

for

such indicators

in Susitna

and Black Lake.

For the second estimate,

we collected empirical

data

on population composition during density estimation

procedures

in MidSu and UpSu using capture-mark-

resight (CMR) techniques (Miller et al. 1997). The

CMR technique

requires

a series of replicated

searches

(typically

1 search/day)

of a defined search

area

using 3-

4 fixed-wing aircraft

(PA 18). Both previously radio-

marked

bears and unmarked

bears were in the search

area. When unmarked

bears were observed they were

captured

and radiomarked.

At the end of the density

estimate

we had a total number

of individuals

of known

sex and age that

had been in the study

area

at least once.

However, some individuals

were in the study area

than others. To correct for this bias we calculated

composition by weighting each individual known to

have been present

on the study area

during

at least one

replication by the proportion of replications during

which radio telemetry indicated that individual was

present.

For our last estimate, teams of pilots (all of whom

were experienced

bear guides) and biologists assigned

unmarked bears in Black Lake and Katmai into

recognizable categories: adult males, medium-sized

bears of unknown sex, subadults, and family groups.

We have no test of the accuracy of these assign-

ments and acknowledge

that they should be interpreted

cautiously. We divided the number of adult males

(marked

+ visually classified unmarked

adult males)

by the number

of bears

seen during

CMR flights

to esti-

mate the percentage

of adult males in Black Lake and

Katmai. Additionally, we estimated composition from

bears

captured

during

the first

2 years

in each study

area.

Estimation of population composition based on data

collected during CMR density estimates was not pos-

sible in Black Lake and Katmai

because of the higher

bear

density in these coastal study areas.

Population density

Population density in MidSu, UpSu, Denali, Katmai,

and Black Lake was estimated using the maximum

likelihood estimator and CMR procedures

described

Miller et al. (1997). No method was available to test

for significance

of differences in density estimates ob-

tained using this estimator,

so comparisons

were based

on overlapping

confidence intervals (G. White, Colo-

rado State University, Ft. Collins, Colorado, USA,

personal communication,

2003). Separate

density esti-

mates were calculated

for independent

bears (offspring

accompanying

adult females were excluded) and for all

bears

(including dependent offspring,

Miller et al. 1997).

Density was reported

for Denali in units of independent

bears by Keay (2001). Here we also estimated

density

for bears of all ages in Denali using methods of Miller

et al. (1997) for comparison

with densities reported

Scandinavia

and southern

Canada.

Survival estimates

Cub survivorship. Survival

rate for cubs accom-

panying radiomarked

females was based on periodic

observations

from aircraft

to count cubs. In most cases

cubs were not radiocollared.

Monitoring to determine initial litter size occurred

during

the first 3 weeks of May (1 flight/week,

weather

permitting) when females accompanied by neonatal

young emerged from dens (Miller 1990d). Subse-

quently, monitoring to determine survivorship was

less intense (0.5-2 flights/month).

During

the period of

den entrance

(late September

and

early

October

in GMU

13; mid October to early November on the Alaska

Peninsula), more frequent

monitoring

was resumed to

count cubs before den entrance. The date midway

between

the last time a cub was seen with its mother

and

the first

time it was missing from the litter

was used as

the date of mortality.

Cub survivorship

was calculated

using the staggered

entry Kaplan-Meier

technique (Pollock et al. 1989).

Annual survivorship was calculated from emergence

from dens as newbors to emergence as yearlings the

following spring. Mortality of an entire litter was

assumed when a female bear with cubs died. In cases

where we lost contact with radiomarked females

accompanied by cubs (possible radio failures, de-

struction

of transmitters

by hunters,

dispersal,

or other

causes), the cubs were treated

as censored

data

(Pollock

et al. 1989). Tests of differences in survival rate

between areas were conducted

using the log rank test

(Pollock et al. 1989). To compare survivorships

between Susitna and Denali, data for Susitna were

Ursus 14(2):130-152 (2003)

HUNTING EFFECTS ON

CUB

SURVIVORSHIP

* Miller et al. 137

collapsed into 6 monthly categories (May-Oct) to

match data from Denali.

In Susitna, data on first year cub survivorship

was

calculated

for 2 seven-year

periods

(1980-86, 1990-96).

Each of these periods

included

the 5-year

period

before

our density estimates in the MidSu area (1985 and

1995), the year of the density estimate,

and the follow-

ing year. Cub survivorship

was also calculated

for the

intervening

period (1987-89) and for the entire period

(1980-96).

For data from Susitna, a logit log-linear model

(Agresti 1990) was used to determine

if survivorship

in a litter

of bear cubs was explained

by 3 variables:

(1)

period (1980-1986, 1990-1996), (2) female age (<8

years old or >9 years

old), or (3) litter

size (1, 2, or >3;

199 cubs in 94 litters, range 1-4 (Miller 1997a). We

considered female age a surrogate

for maternal

experi-

ence; 98% of 72 radiomarked

females produced

a litter

by age 8. Eleven females were in the sample for each

period;

these were older and presumably

better

mothers

during

the second period.

For both pairs

of study areas,

multinomial

tests (Analytical

Software

2000) were used

to test hypotheses

that

the number of cubs dying during

the breeding season (May-Jun) and the non-breeding

season (Jul-Oct) was the same as expected

based on the

length of these periods.

In the Black Lake study area, hunting seasons were

open during alternate regulatory years (fall of odd-

numbered

years and spring

of the following year). This

permitted

evaluation of cub survival within the same

area

during years following open hunting

and following

years after

hunting

was closed.

Adult survivorship. Survivorship for bears >5

was calculated for radiomarked

bears using the stag-

gered entry Kaplan-Meier procedure (Pollock et al.

1989). When a radiomarked

bear was tracked for

a number of years, each year's data were treated as

independent.

Age and reproductive parameters

We calculated

observed

mean age of first

litter

based

on the age at which radiomarked

nulliparous

females

were first observed with a litter. This underestimates

actual mean age for females because of a bias against

females

that

are

late in producing

their

first

litter

or those

that

die prior

to producing

a litter

(Garshelis

et al. 1998).

We corrected

for this bias by assuming

that

females that

had not produced

a litter

at an age greater

than

the mean

age produced a litter in the year following their loss

through

mortality

or signal loss. This procedure

gener-

ated a mean age at first litter less biased by premature

loss of females producing

a litter at older ages. Litter

size was calculated

based on first

observation

out of the

den. Because of small numbers

of litters with 4 cubs,

litters of 3 and 4 cubs were combined for X2

tests of

independence. We also calculated the proportion of

litters

losing all cubs and the proportion

of those losing

some cubs that lost all cubs.

For the Alaska Peninsula studies, mean age was

calculated

based on age of captured

bears.

For studies

Susitna,

mean age was based

on marked

bears

present

the density

estimation

area

during

the density

estimation

study.

Biomass

For Alaska Peninsula studies, biomass was calcu-

lated separately

for adult

males, adult

females, subadult

males, subadult

females, yearlings, and cubs based on

mean weight at capture in mid-May-mid-June. For

cubs and yearlings, we supplemented

our limited data

with weights reported

by Glenn (1980) from captures

in June. Mean weights were multiplied

by the density

of individuals in each category. Density of each sex

and age group was calculated based on proportion

the population

as estimated from population

composi-

tion information

described

above. Biomass for UpSu in

1979 was previously reported

as 1.3 kg/km2 based on

captures during May-early June (Miller and Ballard

1982). In Denali, bears were captured and weighed

during May as well as September

(Keay 2001); only

May data were used to compare with weights from

Susitna. In all study areas, we used a spring scale

suspended from a helicopter or the helicopter's

integrated digital scale to weigh large bears and

a hand-held spring scale to weigh small bears. We

used 2-way analysis of variance to evaluate the

importance of location (coastal or interior) and

treatment (hunted or unhunted) for captured and

weighed female bears >5 years old (Analytical

Software 2000).

Identity of infanticidal bears

Few attacks

on litters

have been observed,

and

the sex

residency

status

of the attacker

is rarely

known.

data

presented

here,

we supplemented

the

data

from

McLellan

(1994) for several protected

and hunted

populations

Alaska. We included nonlethal attacks

that resulted in

injury

to dependent

offspring

or permanent

separation

cubs that

likely led to their

deaths.

Protected

populations

were at McNeil River State Game Sanctuary,

Katmai,

and Denali and included data reported

by Glenn et al.

(1976), Dean et al. (1986), Olson (1993), and Hessing

and Aumiller (1994), plus more recent cases witnessed

Ursus 14(2):130-152 (2003)

138 HUNTING

EFFECTS ON CUB SURVIVORSHIP

* Miller et al.

*AII bears

*All males

50 ..--

All males >5.0

40 -- - - . . .-

Subunit 13E

~ 1965-97 *n

,30

= ??

20-- - - ------- --------- --- -----

A A A A

0 a An

1960 1965 1970 1975 1980 1985 1990

Regulatory year

Fig. 3. Trends in brown bear harvests in south-central

Management Subunit 13E, 1965-97.

by agency personnel

or documented

during

radiotelem-

etry flights in Katmai

and Black Lake.

Results

South-central Alaska studies: changes in

population composition in Subunit 13E

Inferences from harvest data. Numbers of bears

harvested

in Subunit 13E (including

MidSu and UpSu)

trended upward during 1965-97 (Fig. 3). Years of

maximum harvest were 1982-86 and 1995-96, when the

bag limit was 1 per

year

instead of 1 per

4 years

(Fig. 3).

During 1965-97, significant

increases

in kills occurred

for all bears

(F= 78.9; = 1.3; 1, 31 df; P < 0.001), for

males of all ages (F = 48.3; P = 0.6; 1, 31 df; P <

0.001), and

for males >5 years

old (F= 22.2; = 0.3; 1,

31 df; P < 0.001; Fig. 3). The rate

of increase

in harvest

during our study period was less dramatic; this

suggested a preexisting harvest impact on bear abun-

dance.

During 1979-97, the kill of all bears increased

= 12.1; P = 1.3; 1, 17 df; P = 0.003). Positive slopes

occurred as well, for kills of males >5 years

old and for

kills of males of all ages, but these were not significant

(F=0.6; P3-0.14; 1, 17 df; P 0.46 and F = 2.7; p,=

0.4; 1, 17 df; P = 0.12, respectively).

A total of 912 bears of known sex and age were

reported killed in Subunit 13E during 1965-97. Of

these, 55% were males. Males consti-

tuted 57%

of 592 bears <5 years

old in

* * the harvest and 51% of 321 bears >5

....---------------- --- years old (Fig. 4). Males constituted

39-67% of the annual

harvest

(3-year

running averages, Fig. 4). The sharp

-...*

--------- decline in the proportion

males in the

hunter

kill of bears >5 years

old during

the early 1990s (Fig. 4) was consistent

* with an interpretation that adult males

were less abundant

in the population

*-.-.-. . .... adult bears than

previously.

This inter-

* pretation

was consistent with data on

population

composition

(see following

----------- section) that indicated reductions in

AA A abundance of adult males.

A A Harvest rate of marked males (17%

based on 194 marked

bear-years)

was

1995 2000 also higher than for marked females

(8% based on 441 marked

bear-years)

during 1980-95 (X2

= 8.9, P = 0.003).

Alaska's Game For both sexes combined, harvest rate

of marked bears

was 10.8%;

this value

is biased toward

females because

females were radiomarked

than males. In Subunit 13E,

harvest rate was calculated

as 22%

(possible

range

= 15-

40%) based on known kills and the range

of population

estimates (Miller 1992, 1993b). Over the 16-year study

in Subunit 13E, adult

male kill density was 0.54 males

>5 years old killed/year/1,000

km2.

The harvest of more males than females did not

reflect differences

in sex ratio at birth. Sex ratio at exit

from dens was not different from 50:50 for 19 male and

16 female neonatal cubs handled between 6 May and 5

June during 1979-93 (X2 = 0.61, P = 0.43; Miller

1997a).

Measured changes in population composi-

tion. There were fewer males in the population

of bears

using MidSu during the 1995 density estimate than

during

the 1985 density

estimate

(x2 = 14.1, P < 0.001;

Table 1). There were also fewer older males (>5 years

old) in 1995 than in 1985 (x2 = 4.83, P= 0.02; Table 1).

Sex ratio for bears >5 years old at time of first

capture

was 70 males: 100 females

during

1980-85 (n

= 34 bears

captured)

and 43 males:100 females during 1993-95

(n = 30 bears).

This difference was not significant

(X2

0.86, P = 0.35).

Between 1985 and 1995, there were no significant

differences

in mean age of females present

at least once

in the density

estimation

area for females >2 (Wilcoxon

rank sum test, P = 0.81) or for females >5 (P = 0.86).

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS ON CUB SURVIVORSHIP

* Miller et al. 139

Similarly, there were no significant 90

differences

in mean age of independent

males (P = 0.46) or for males >5 (P = 80

1.0; Table 1).

>70

South-central Alaska studies:

Temporal changes in cub . , 60

survivorship

The Susitna survival rate of cubs 50

was similar during 1980-86 (0.67,

95% CI = 0.55-0.79) and 1990-96 E 40

(0.64, 95% CI

= 0.52-0.77) (X = 0.08, |

1 df, P = 0.78; Table 2). Overall,

mean

cub survival 1980-96 was 0.67 (95% 30 ingsaed?

CI = 0.60-0.75, Table 2). Approxi-

mately half of the litters experienced 2067 68 69 70 71 7:

no losses during both earlier and later

periods (Table 2). There was also no

change in the frequency

of whole litter Fig. 4 Perce

loss between periods (X2

= 0.02, P = and >5 years

0.87; Table 2). Over the whole study average).

period, 28% of cub litters observed

were completely lost between den exit

and den entrance

the following fall (Table 2).

None of the factors examined in the logit log-linear

model influenced cub survivorship.

Cub survivorship

was not correlated

with period (X2

= 0.08, P = 0.78),

female age (X2

= 0.03, P = 0.79), or litter size (2 = 0.96,

P = 0.62).

South-central Alaska studies: Spatial

comparisons of cub survival rates

In hunted

Susitna,

cub survivorship

was almost

twice

that in nearby

unhunted Denali (X2

= 20.58, 1 df, P <

0.001; Table 3). In Susitna,

adult male survival

and, by

1995, proportion

of males in the adult population,

was

lower than in Denali (Table 3).

The rate of loss of entire litters was higher in

unhunted Denali than in the hunted population in

Susitna

(Table

3; X = 12.2, 1 df, P < 0.001). However,

the proportion

of litters experiencing loss of >1 cub

where the entire litter

was ultimately

lost was higher in

hunted Susitna

(Table 3; X2

= 7.7, 1 df, P = 0.006).

Alaska Peninsula studies: Changes in

population composition

Inferences from harvest data. During 1987-96,

guided nonresident hunters killed 72% of brown bears

taken

in Subunit 9E (n= 1,520), which encompasses

the

Black Lake study area; resident hunters killed 28%.

Males composed 66% of the total harvest and 74% of

Bear kills

Subunit 13E

1967-2001

Bears >5 years-old 1967-2001

ears <5 years-old

Bag limit

= 1/year <

ison

1980 \'---...~..... ,Study period

2 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 0 1

Regulatory year

nt males in harvests of brown bears aged <5 years old

old in Alaska's Subunit 13E, 1967-2001 (3-year running

harvested bears >5 years old. Forty-nine percent

of all

males in the harvest were >5 years

old, and these males

averaged 11 years old. Sellers (1998) estimated a

population of 3,200 brown bears in areas of Subunit

9E open to hunting.

Based on this estimate,

the overall

annual harvest rate (known kills plus estimated un-

reported

kills) was 5.0% during 1987-96.

Harvest rates of marked bears in Black Lake also

indicated a hunter bias toward males. By 1999, 31% of

all males marked

in 1988-92 (n = 35) were taken by

hunters compared to only 15% of females (n = 45).

Minimum annual harvest

rates of marked bears during

1988-92 were 9% for adult males and 2% for adult

females. Including

subadult

bears,

the harvest rates

were

9% for males and 4% for females.

In contrast, only 2 bears marked in Katmai were

killed by hunters

during 1989-2000. Both of these were

adult males killed outside

the park

boundary,

at least 85

km south of their capture locations. Forty-eight adult

males were marked throughout the entire study in

Katmai, including bears originally marked when they

were <5 years old that became >5 during the study.

Based on radiotracking

data, we estimated an annual

survival rate for adult males in Katmai of 0.96 (95%

CI = 0.72-1.0). Using this survival rate, we estimated

a total of 225 marked adult male bear-years were

available

during 1989-96. This estimate and the kill of

2 adult males were used to calculate an annual harvest

Ursus 14(2):130-152 (2003)

140 HUNTING

EFFECTS

CUB

SURVIVORSHIP

* Miller et al.

Table 1. Temporal changes in brown bear populations in the Middle Susitna (MidSu) study area of

southcentral Alaska during a period of increasing hunting pressure between 1985 and 1995 based on

independent bears (excludes offspring still with their mothers).

1985

Replications

in density

and composition

estimate

Density

of independent

bears, both

sexes/1,000 km2

(95%

Cl)

Density

of independent

males/1,000 km2

(95%

Cl)

Independent

bears

Males

Females

Males

(%)

Males >5 years old

Females >5 years old

Males

(%)

among bears >5 years old

Weighted

number

of independent

bears

Males

Females

Males

(%)

Males >5 years old

Females >5 years old

Males

(%)

among bears >5 years old

Male

survivorship

based on radiomarked

bears >2 years old (95%CI)

Female

survivorship

based on radiomarked

bears >2 years old (95%CI)

18.8 (15.2-24.3)

9.3 (7.0-14.4)

45.2a

43.5a

7.6

10.9

41.1a

5.0

8.3

37.6a

0.82 (0.6-0.95, n 7

deaths during

1980-85)

0.90 (0.84-0.96, n = 9

deaths during

1980-85)

23.3 (19.3-30.1)

3.6 (2.4-14.7)

20.0a

22.2a

3.0

14.6

17.1a

2.6

10.2

20.3a

0.71 (0.38-1.0, n - 2

deaths during

1991-95)

0.90 (0.85-0.97, n - 3

deaths during 1991-95)

Median

age

Independent

males

Males >5 years old

Independent

females

Females >5 years old

aSignificant

difference

between 1985 and 1995 (P < 0.05).

rate for adult

males of 0.9% in Katmai.

Overall,

4% of

all males marked

at Katmai

were killed by hunters

2000, which was significantly fewer (x2 = 11.3, P =

0.001) than at Black Lake. The harvest rate for all

other marked cohorts at Katmai was 0% (315 adult

female bear-years,

38 subadult

male bear-years,

and 25

subadult

female bear-years).

We inferred

that the male-

biased harvest in Black Lake resulted in fewer adult

males in the Black Lake population

than in the Katmai

population.

Measured changes in population composi-

tion. During CMR density estimation flights, adult

males made up a higher percentage

of all bears seen in

Katmai

(20.0%,

n = 456) than

at Black

Lake (10.9%,

n =

607; x2 = 17.06, P < 0.001). The sex ratio of bears

captured

during 1989-90 in Katmai (including uncap-

tured companions of consorting pairs) was 79 adult

males:

100 adult

females

compared

to 39 adult

males:

100

adult

females at Black Lake (X2

= 3.32, P = 0.07). The

sex ratios of captured subadult bears did not differ

between the 2 areas:

122 males:100 females (n = 38) at

Katmai and 127 males:

100 females (n = 36) at Black

Lake (X2 = 0.06, P = 0.8).

There were proportionally

more subadults

at Black

Lake than at Katmai.

Subadults

made up a significantly

smaller

percent

of all bears >2 years old in the capture

sample

from

Katmai

(16%)

than

Black Lake (44%;

14.95, P < 0.001). Subadult

males

comprised

20%

of all

males >2 years

old captured

Katmai,

compared

to 58%

at Black Lake (x2 - 11.92, P = 0.001). Subadult

females

comprised 12% of all females captured at Katmai,

compared

to 33% at Black Lake (X2

- 4.85, P = 0.03).

The mean

age of adult

males at Katmai

was 10.7 years

(n = 28) and was 9.7 at Black Lake (n = 15; Wilcoxon

Rank Sum, P = 0.65). The mean ages of adult females

were 10.8 and 12.6 at Katmai and Black Lake,

respectively

(Wilcoxon Rank Sum, P = 0.13).

Alaska Peninsula studies: Spatial differences

in cub survivorship

In the hunted

brown bear population

at Black Lake,

cub survivorship

was significantly

higher

(2 =7.7, 1 df,

Ursus 14(2):130-152 (2003)

9.2 (9)

12.4 (10)

10.1 (8)

10.7 (15)

11.0 (8)

12.4 (8)

11.6 (8)

15.1 (12)

1995

HUNTING

EFFECTS

CUB

SURVIVORSHIP

* Miller et al. 141

Table 2. Temporal comparisons of cub survivorships and litter loss (percent) in Alaska's Middle

and Upper

Susitna (MidSu

and UpSu) study areas during periods of increasing hunting pressure (95%

Cl, n = number of

cubs accompanying radiomarked

females). Rates calculated from den exit as newborn cubs until den entrance

the following fall.

Individual

cub survivorship

Litters without

mortality

Partial

litter

loss

Whole litter loss

1980-86 (moderate hunting)

0.67 (0.55-0.79, n = 64)

52.1%

(n= 13)

24.0% (n = 6)

24.0%

(n = 6)

1990-96 (heavy hunting)

0.64 (0.53-0.77, n = 63)

51.9%(n= 14)

25.9%

(n = 7)

22.2%

(n = 6)

1980-96a

0.67 (0.60-0.74, n = 167)

48.7%

(n = 37)

23.7%

(n = 18)

27.6%

(n = 21)

alncludes

1987-89, not included

in the previous

columns.

P = 0.006) than in the unhunted

population

at Katmai

(Table

4). Bear density and

biomass was lower at Black

Lake than in Katmai

(Table 4). Biomass at Black Lake

was about 19 times higher

than in Susitna

(1.3 kg/km2,

Miller and Ballard 1982). The limited data based on

radiomarked males were consistent with an interpreta-

tion that adult male survivorship

was lower

in the hunted

population

at Black Lake than at Katmai

(Table 4), but

small sample

sizes of marked males precluded detecting

a significant

difference

(X2

= 0.08, 1 df, P = 0.78).

The rate of loss of entire litters was higher

in Katmai

than Black Lake (Table 4; X2

= 4.8, 1 df, P = 0.02).

Unlike our Susitna studies, the proportion of litters

experiencing

loss of >1 cub that were completely lost

was higher in unhunted Katmai than in Black Lake

(Table

4; x2 = 9.6, 1 df, P = 0.002).

Alaska Peninsula studies: Temporal

differences in cub survivorship

On the Alaska Peninsula, cub survival rates were

compared following seasons when bear hunting was

open and

closed during

the

preceding

spring

and

autumn.

In the Black Lake study area

during

1988-95, survivor-

ship of cubs accompanying

radiomarked

females (to den

entrance)

was 0.60 (95%

CI= 0.44-0.67) following open

hunting

seasons. Following closed hunting

seasons, cub

survivorship was 0.65 (95% CI: 0.51-0.79). These

differences were not significant (2 = 0.03, 1 df, P =

0.86). Similar comparisons for cub survivorship

data

only during the period from den emergence through

June 30 (the primary

breeding season) were also not

significant

(2 = 0.63, 1 df, P = 0.43).

Additional comparisons

Density and kill density. Based on overlapping

95% confidence intervals, bear density in MidSu was

not different

between 1985 and 1995 (Table 1). In spite

of intensive harvests, during 1980-1997 population

growth (k) calculated

from survivorship

and reproduc-

tive data from radiomarked bears was 1.02. Measured

density of independent

males was not significantly

dif-

ferent

between 1985 and 1995 (Table 1). Both measure-

ments of density had large confidence intervals

(Table

1). Preliminary

results based on surveys conducted in

2003 suggest

that

bear

populations may have declined

GMU 13 since our Susitna studies ended in 1997 (E.

Becker, Alaska Department

of Fish and Game, Anchor-

age, Alaska, personal

communication

2003).

Based on non-overlapping

confidence intervals, in-

dependent bear density was higher in Denali than in

MidSu (Table 3). Bear density was higher in Katmai

than at Black Lake (Table

4).

In Subunit 13E (which includes our Susitna study

areas),

average

annual

adult kill density was 0.54 males

and 0.45 females per 1,000 km2. Kill density in 13E

(1961-91) was higher than in any other management

area in interior

Alaska (Miller 1993b).

We know of no bears killed within the Denali and

Katmai study areas during our studies. Annual adult

male kill density at Black Lake was 3.1/1,000 km2

(annual range 2.1-3.7). Adult female kill density at

Black Lake was 1.1/1,000 km2 (annual

range 0.9-1.3).

Reflecting

the higher bear density at Black Lake, adult

male kill density was about 6 times higher and adult

female kill density about

double that in Subunit 13E.

Bear body mass. In both Susitna and the Alaska

Peninsula samples, bears were heavier in the hunted

populations than in the nearby unhunted population.

Mean weights for adult females were about a third

higher in the hunted

populations

in Susitna

than in the

unhunted

Denali population

(Table 3). Similarly,

mean

adult female weights were about 20% higher in the

hunted Black Lake population than in the unhunted

Katmai population (Table 4). Two-way analysis of

variance on weight of females >5 years old revealed

that the most significant determinant of weight was

whether

bears were coastal or interior

(F = 561; 3,157

df; P < 0.001) followed by whether they were in

a hunted area (F= 170; 3,157 df; P < 0.001). The

Ursus 14(2):130-152 (2003)

142 HUNTING

EFFECTS

ON CUB SURVIVORSHIP

* Miller et al.

Table 3. Demographic comparisons between a heavily hunted brown bear population in south-central Alaska

(Susitna study areas in Subunit 13E), 1980-97, and an unhunted population in nearby Denali National Park

and

Preserve, 1991-98.

Susitna Denali National Park

Parameter Value n Value n

Cub survival 0.67 167 0.34 88

(95% CI) (0.60-0.75) (0.24-0.44)

Adult

(>5 yr)

female survival

(1980-95) 0.92a 257b 0.97125

(95% CI) (0.68-0.92)a

Adult

(>5 yr)

male survival

(1980-95) 0.80a 63a 0.98 59b

(95% CI) (0.68-0.92)a (0.95-1.0)

Males (%)

among bears >5 yr

old 35 (1985) - 36

21 (1995)

Litters

lost (%) 26 74 59 41

Litters

(%) losing

>1 cub

that lose all

cubs 50 38 17 29

Density

(independent

bears/1000

km2)

in 1985 18.8

(spring) - -

(95% CI) (15.2-24.3)

Density

(independent bears/1000

km2)

in 1995 23.3

(spring) -34.7 (fall)

(95%

CI) (19.3-30.1) (32.2-38.7)

Mass

(in

spring)

of females

(kg)

>5 yr

old 133 50 98 65

SD 17.9 13.7

Mean

age of independent

males 9.2 (1985) 14 (1985) 9.5 21

11.0

(1995) 5 (1995) -

Mean

age at weaningc 2.1d 54 2.9d 19

Mean

age at first

litterc 5.6d 37 10.3d 15

aData from 1980-95.

bBear-years.

CCalculated

based

on age in

whole

numbers

(2.5 yrs-old

= 2).

dData

from Miller

(1997a).

interaction term between area and hunting was not

significant

(F = 0.19; 1 df; P = 0.67). Mean age of the

adult

female bears

weighed in each area

was 15.3 years

in Denali (n = 65), 14.1 in Black Lake (n = 34), 12.8 in

Katmai

(n = 11), and 12.5 in Susitna

(n = 50). Ages of

weighed adult female bears did not differ among the 4

areas (Kruskal-Wallis

one-way analysis of variance

5.3; 3, 157 df; P= 0.15).

Cub survivorship in Denali and Katmai. Bears

in Katmai rely on salmon consumption to maintain

high densities while diets of Denali bears do not in-

clude salmon. Regardless, cub survivorship did not

differ between these 2 unhunted populations (0.34;

Tables 3 and 4).

Timing of cub mortality. In Katmai,

62% of the

cubs lost (n = 50) were lost during breeding season

compared

to 35% at Black Lake (n = 37 cubs lost). In

Denali, 54% of cubs lost (n = 58) were lost during

breeding

season compared

to 67% (n = 51 cubs lost) in

Susitna. Based on expected values calculated

from the

length of these periods, these differences

were signifi-

cant at Katmai (x2 = 18.5, P < 0.001), Denali (x2=

10.6, P = 0.001), and Susitna (x2 = 25.5, P < 0.001),

but not at Black Lake (X2

= 0.05, P = 0.8).

Litter sizes. The distribution

of litter

sizes differed

between Black Lake and Katmai

(X2

= 11.3, 2 df, P =

0.003). Mean litter size at emergence from dens was

smaller

in Katmai

than at Black Lake (Wilcoxon rank

sum test, P < 0.001; Table 5).

Mean litter size at emergence from dens was 2.1 in

both unhunted

Denali and in heavily hunted Susitna

(Wilcoxon rank

sum, P = 0.47), and the distribution

litter

sizes was not different

(X2

= 1.75, 2 df, P = 0.41;

Table 5). The distribution

of litter sizes in Susitna

differed between early in the period of heavy hunting

(1980-86) and later

(1990-96; X2

= 6.9, 2 df, P = 0.03).

This resulted

from decreased

proportion

of litters of 2

cubs and

increased

proportion

of litters

of 3 cubs later

the period of heavy hunting. There was a significant

difference between numbers of litters <2 cubs and

litters

of >3 cubs between 1980-86 and 1990-96 (x2=

6.32, 1 df, P = 0.01). However, mean litter sizes were

not significantly

different

between these periods (Wil-

coxon rank

sum test, P = 0.12).

Bears attacking family groups. Cases from

hunted

populations

on the Alaska

Peninsula

and Kodiak

Island

include

published

accounts

by Troyer

and Hensel

(1962), observations

made

during

radio-telemetry

flights

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS

CUB SURVIVORSHIP

* Miller et al. 143

Table 4. Demographic comparisons on the Alaska Peninsula between a moderately hunted brown bear

population at Black Lake and an unhunted population in Katmai

National Park

and Preserve.

Black

Lake

(1988-96) Katmai

(1989-96)

Parameter Value n Value n

Cub

survival 0.57 107 0.34 99

(95%

CI) (0.48-0.67) (0.26-0.42)

Adult

(>5 yr)

female survival

(1980-95) 0.90 229a 0.91 210a

(95% CI) (0.86-1.00) 0.87-0.95

Adult

(>5 yr) male survival

(1980-95) 0.75 9a 0.96 25a

(95%

Cl) (0.33-1.00) (0.72-1.0)

Males (%)

among bears >5 yr old 28b 43b

Adult males (%) among all bears 11c 456c 20c 607C

Litters lost (%) 14 37 35 43

Litters

(%)

losing >1 cub that lose all cubsd 24 21 69 26

Density

(independent

bears/1000

km2) 122e 412e

(95% CI) (108-139) - (325-545) -

Mass (in

spring)

of females (kg) >5 yr

old 200f 34 162 12

SD 34.7 31.8

Bear biomass (kg/km2) 24 82

Mean

age of independent

males 6.9 32 9.2 35

Mean

age at weaningg 2.4 33 2.7 25

Mean

age at first

litter9 6.3 8 7.2 12

aBear-years.

bBased

on sample of bears captured.

CBased

on aerial classification of bears observed

during capture-mark-resight

survey

flights.

dExcludes litters lost when mother died.

eData

from Miller

(1997a).

fincludes

4 males weighed during

this study

and 21 weighed by L.

Glenn

(Alaska Department

of Fish

and Game,

Anchorage,

Alaska,

USA, unpublished

data collected at Black

Lake

during

1970-77).

gCalculated

based on age in whole numbers

(2.5 yrs-old

= 2).

and accounts

by experienced

hunting guides. In total, 19

attacks

were documented,

and in all cases the attackers

were adult males. In 8 cases the age of the males

involved was known and averaged

9.4 years (range 5-

15). Most documented

attacks in hunted

areas

occurred

during

the breeding

season, but

this may reflect the large

number of hunting guides in the field during

the spring

bear season. In only 1 case was the killer known, and

this was a 14-year-old

resident

male bear.

In unhunted areas on the Alaska Peninsula, adult

males were identified

as the attackers

in all 4 cases that

occurred

during

the breeding

season. Because most eye-

witness accounts occur when bears are congregated

Brooks River in Katmai and McNeil River during the

peak

of salmon

availability,

the timing

of these incidents

is biased

toward

mid- to late-summer.

Adult

males were

identified

either

directly

or by circumstantial

evidence to

have been the attacker

in 10 of the 13 cases where the

identity

of the killer

was known. Adult

females were the

attackers in the other cases (Hessing and Aumiller

1994). In at least 8 adult

male cases, the perpetrator

was

classified by observers to be a resident based on his

presence

during

previous years.

Discussion

Information on population regulation mechanisms

in bears is difficult to obtain, and it is not surprising

that information

gaps are sometimes filled by inference

and speculation.

Comparisons

between study areas

may

be confounded by habitat differences that are poorly

documented

or understood.

Comparisons

within an area

subjected to different treatments over time may be

confounded

by small sample sizes that yield estimates

with low precision

or biased key parameters.

Further, it is difficult to obtain unbiased data on

population composition. Carrying

capacity as well as

vital rates for bears may vary stochastically between

years and this variability may confound studies of

density dependence. Our studies in Alaska are not

immune to these problems but are nevertheless in-

structive

regarding

effects of hunting on hypothesized

changes in vital rates of bears. We summarize key

characteristics of our 4 Alaska study areas in Table 6.

Our studies in Alaska do not support earlier

suggestions that hunting biased toward male brown

bears increased cub survivorship. Similarly, other

reviews (Miller 1990b, Derocher and Taylor 1994,

Ursus 14(2):130-152 (2003)

144 HUNTING

EFFECTS ON

CUB

SURVIVORSHIP

* Miller et al.

,, ,

Garshelis 1994, McLellan 1994, Taylor 1994) found

inconclusive evidence for such compensatory

effects.

Our studies included spatial comparisons between

hunted areas and unhunted areas. We also made tem-

poral comparisons

of cub survivorship

within a period

of increased harvests during which male abundance

declined in a portion of interior

Alaska. For a portion

of coastal Alaska, we also contrasted

cub survivorship

following years in which hunting

was open and closed.

We examined both low density interior populations

and high density coastal populations where salmon

was a significant

component

of diets. Cub survivorship

was higher in the hunted Alaskan populations

than in

the unhunted populations. This finding is consistent

with a decline in cub survivorship

in bear populations

living near carrying capacity in unhunted

parks com-

pared to populations

in similar habitats with hunting-

induced reductions

in density to levels below carrying

capacity.

We found no differences in cub litter sizes be-

tween hunted

and

nearby

unhunted

areas

in southcentral

Alaska (Denali and Susitna).

In contrast,

on the Alaska

Peninsula, litter sizes were larger in a hunted area

(Black Lake) than

in nearby,

unhunted

Katmai

National

Park.

In Susitna, with increasing hunter harvest and a

declining

proportion

of adult

males

in the population,

found

no significant

differences

between

mean cub litter

sizes early and late in the period of increased

hunting.

However, we did find a significant increase in the

proportion

of 3-cub litters

and decline in proportion

of 2

cub litters later in the period of intense hunting

compared to the earlier period. Although we do not

conclude

this, our

litter

size data

from

Susitna

were

consistent

with an increase

in litter size correlated

with

hunting

rather

than

with a decline, as would be expected

from the hypothesis advanced

by Wielgus and Bunnell

(2000). Wielgus and Bunnell (2000) and Wielgus et al.

(2001) were careful to clarify that their conclusions

might apply only to very small populations

at the edge

of the species' range.

Our results from Alaska differed from the predic-

tions of Swenson et al. (2001b) and Swenson (2003) in

Scandinavia

and

Wielgus and

Bunnell

(2000) in Canada.

Although these authors

proposed

different

mechanisms

for their findings, both of these studies concluded that

removal of males through

hunting

had negative effects

on brown

bear

populations.

The disparity

between their

results and ours merit an examination

of their studies

and the factors that may help explain our different

conclusions.

Table 5. Litter sizes for litters of newborn cubs in

south-central and coastal study areas in Alaska.

Litter

size is based on first observation subsequent

to emergence from dens. Data for Denali from Keay

(2001 and unpublished data).

Number of litters

Study Mean

area 1 cub 2 cubs 3 cubs 4 cubs litter

size

Black Lake 4 14 26 2 2.57

Katmai 11 26 14 0 2.06

Susitna 8 26 4 1 1.95

(1980-86)

Susitna 7 14 13 0 2.18

(1990-96)

Susitna 17 50 23 1 2.09

(1980-96)1

Denali 5 28 9 0 2.1

'Includes

data

from 1987-89 not included

in other rows.

Comparisons between Alaskan, Scandinavian,

and Canadian studies

Proportion males removed in Scandinavian

studies. The rate

of male removal

in the hunted

areas

in Susitna in Alaska was approximately

twice that in

Scandinavia.

In hunted southern

Scandinavia,

11 adult

males were killed during

the 12-year

period Q(

= 0.92/

year, range 0-4; Swenson et al. 2001b). Based on an

average size (4,108 km2) of cub areas as defined by

Swenson et al. (2001b), approximately

0.22 adult

males

were killed annually

per 1,000 km2 of cub area. Adult

male kill density in Subunitl3E was 0.54/1,000 km2.

Density for bears

of all ages was similar

in the hunted

Susitna area and in the hunted area in southern

Scandinavia.

In southern

Scandinavian,

density varied

between 8 and 20 bears of all ages/1,000 km2

(J. Swenson, Norwegian Institute

for Nature

Research,

Trondheim, Norway, personal communication, 2003)

based on methods described

by Swenson et al. (1994).

In Susitna,

density

was 27 bears

of all ages/1,000 km2

the MidSu area

(in 1985) and 11 bears

of all ages/1,000

km2 in the UpSu area

(Miller

et al. 1997).

Swenson et al. (2001b) estimated

that a 20% kill of

adult males in southern

Scandinavian

resulted in their

reduced

cub survival. This was not an annual

rate but

rate

"for

the

years

in which

adult

males

died"

(Swenson

2001b:76). In Susitna,

we estimated

a 17%

annual

har-

vest of males based on marked

males of all ages.

These comparisons

suggested that a decrease in cub

survivorship

from

adult

male removal

by hunters

similar

to that

suggested

by Swenson

et al. (2001b) should

have

been evident in our hunted area in Susitna in south-

central

Alaska.

Because we did not detect

this effect, we

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS

CUB

SURVIVORSHIP

* Miller et al. 145

I~~~~~~~~~~~~~~~~~~~~~~,,,

,,,, ,, ,,, , . . . . . . . . . . , ,,,,,

Table 6. Summary of characteristics of Alaska study

areas. K represents carrying capacity.

Southcentral

Alaska Alaska

Peninsula

Hunted

populations

Susitna Black

Lake

Studied

1980-97 Studied

1988-96

Heavy

harvest Moderate

harvest,

approximately

9.5% approximately

Declining proportion Proportion

males prob-

males in population ably

stable

Population

below K Population

below K

Density

(all

bears, UpSu Density

(all

bears)

MidSu,

respectively) = 191/1000 km2

= 10.7-27.1/1,000 km2

Unhunted

populations

Denali

National Park Katmai

National

Park

Studied 1991-98 Studied

1989-96

Human kill

negligible Human kill

negligible

Population

at K Population

at K

Density

(all bears) Density

(all

bears)

= 37.1/1,000 km2 = 551/1,000 km2

conclude

that the conclusions of Swenson et al. (2001b)

are not generally

applicable.

recently,

Swenson (2003) reported

on a manage-

ment

experiment

in Sweden during

which large

numbers

of male bears were killed by hunters.

This experiment

was conducted on a rapidly

growing

population

believed

to be below carrying

capacity. A dramatic

35-fold in-

crease in annual adult male mortality

and a 6-fold in-

crease in annual mortality to all bears resulted in a

reported

doubling

of cub mortality

(Swenson

2003). This

experiment was similar in design to our temporal

MidSu comparisons

but yielded different results with

a much higher

degree of male reduction

in the Swedish

study.

Proportion males removed in Kananaskis

and Selkirk studies. In southern Canada, bear

density (all ages) was reported

as 16.1/1,000 km2 in

Kananaskis

area of southwestern

Alberta

and 16.8/1,000

km2

in the Selkirks

of British

Columbia,

northern

Idaho

and northeaster Washington (Wielgus and Bunnell

2000). Density was calculated based on home range

overlap techniques for 5 radiocollared

adult bears in

Kananaskis

and 9 in the Selkirks

(Wielgus and Bunnell

2000). In the 6,300-km2

Kananaskis

study area,

5 male

bears were reported

shot during 1980-84, an average

of 1/year for an annual adult male kill density of

approximately

0.16 adult males/1,000 km2, about the

same as in southern

Scandinavia.

Based on the (prob-

ably generous) assumption

that a quarter

of the pop-

ulation

density was adult

male, we calculated

an annual

adult

male removal

rate

in Kananaskis

of approximately

4%. This calculated removal rate was less than for

Scandinavia and Susitna. These rough calculations

suggested that any depensatory effect from male

removal in Kananaskis

should also have been evident

in southcentral

Alaska, if the pattern suggested by

Wielgus and Bunnell (2000) was a general

consequence

of male-biased

hunting.

Alaska Peninsula comparisons. Bear densities

in our hunted

and unhunted

areas

in Susitna

and Denali

were similar to densities in Scandinavia

and southern

Canada. Density for bears of all ages for the Denali

study area was 37.1/1,000 km2 (95% CI = 34.4-41.1).

Densities in both hunted and unhunted areas on the

Alaska Peninsula

were much higher: 191/1,000 km2 at

Black Lake and 551/1,000 km2 at Katmai

(Miller

et al.

1997; these density estimates

vary from Tables 3 and 4

because

they include

bears

of all ages). The high density

in our Alaska Peninsula areas probably reflects more

abundant

food, notably salmon, in coastal Alaska com-

pared

to interior

areas

(Miller

et al. 1997). This conclu-

sion was also indicated

by the heavier weight of adults

in the coastal study areas

(Glenn 1980) compared

to the

interior

Alaska (Hilderbrand

et al. 1999).

Katmai

has the highest density currently

documented

for a brown bear population

(Miller et al. 1997). The

annual

harvest

rate

for adult

males at Black Lake (>9%,

roughly) was lower than Susitna and the Scandinavian

studies (Swenson et al. 2001b) but higher

than southern

Canada

(Wielgus and Bunnell 2000).

Proximity to carrying capacity in Alaskan,

Canadian, and Scandinavian studies

Proximity to carrying capacity in our studies was

inferred.

Our inferences were supported

by the higher

densities, higher biomass, lower mortality, and lower

bear weights in the national

park

populations.

We lack data on bear habitat quality that could

suggest that differences in bear weights were caused

solely or primarily

by availability or quality of bear

foods. However, we believe a more persuasive

case can

be made that differences in density and biomass of the

bears

reflecting

proximity

to carrying

capacity

is a more

parsimonious explanation for the weight differences.

We believe the relatively low cub survivorships in

Katmai

and Denali compared

to hunted populations

Black Lake and Susitna,

respectively,

resulted

because

the populations

in the unhunted

parks

were at carrying

capacity.

It is accepted

ecological theory

that

at carrying

capacity, density dependent competition for food and

Ursus 14(2):130-152 (2003)

146 HUNTING

EFFECTS ON CUB SURVIVORSHIP

* Miller et al.

intraspecific predation

would be expected to increase

mortality

rates for dependent offspring and subadults,

decrease reproductive

rates, or both (Andrewartha

and

Birch 1954; Caughley 1966, 1977).

Cub survivorships

in hunted populations

thought to

be below carrying capacity in southern Scandinavia

(Swenson et al. 2001b), central

Alaska, and the Alaska

Peninsula

were

remarkably

similar

(0.65, 0.67, and

0.57,

respectively).

Cub survivorship

in the northern Scandi-

navian population

(0.96) was the highest ever reported

and occurred in a very low density population (16.4

bears/1,000

km2, J. Swenson personal

communication,

2003). Swenson et al. (2001b) and Sather et al. (1998)

thought both Scandinavian populations were below

carrying capacity. The characteristics

of the northern

Scandinavian

population described by Swenson et al.

(2001b) appear

to be rare

(unhunted

but below carrying

capacity and surrounded by a hunted population

producing

few emigrants).

We offer no explanation

for the high cub survivor-

ship observed

in the northern

study area

in Scandinavia

(Swenson et al. 2001b). However, we suggest that

circumstances

described for this area indicate it was

atypical

for naturally-occurring

brown

bear

populations.

If so, this would

make

the northern

Scandinavian

area

inappropriate

model from which to draw general

conclusions about

bear

demographics.

Sample size constraints

The southern Canada study (Wielgus and Bunnell

2000) was constrained

by small sample

sizes. This study

claimed hunting

of adult

males caused females to avoid

preferred

foraging habitats, resulting in reduced litter

sizes (Wielgus and Bunnell 2000). Litter

size (x = 1.4,

SE = 0.24) for marked

females in the hunted

Kananaskis

area of southwestern

Alberta

came from 5 litters over

a 4-year

period.

In the Selkirk

area,

mean litter

size (x =

2.2, SE = 0.13) was based on 10 litters

observed

during

a 6-year

period (Wielgus and Bunnell 2000). The mean

litter size in Kananaskis

was the smallest reported

for

brown bears in North America and was based on the

smallest sample size. This, along with the absence of

differences in other vital rates, suggested that the re-

ported

low mean litter

size for Kananaskis

should

be in-

terpreted

cautiously.

Vital rates

for adult

females during

the period of hunting in Kananaskis

were based on

monitoring only 5 female bears for a total of 11

adult female bear-years (Wielgus and Bunnell 1995:

Table 3).

SSI in Scandinavia and Alaska

In Scandinavia, available data indicated that in-

fanticidal

males were not fathers

of the cubs they killed

(E. Bellemain

et al. unpublished

data

cited by Swenson

2003). The ability of a male to recognize females with

whom he may have fathered cubs and to forego

infanticide

on such cubs would clearly

be advantageous.

Realization of this benefit by males does not require

removal

of males and resulting

increases

in SSI.

Swenson et al. (1997, 2001b:69) originally

reported

that the decreased cub survivorship

he reported was

caused by immigrating

males: "We suggest that immi-

grating males kill cubs, as predicted by the sexually

selected infanticide

hypothesis." More recently, Swen-

son (2003) indicated

that resident

adult

males kill most

of these cubs, and noted:

"... SSI increases

the fitness

a resident

male as much, or more, than an immigrating

male, and

nothing

in the SSI hypothesis

requires

that

the

species be territorial

or social."

Our

observations

agree with the more recent

view by

Swenson (2003); immigrant

males need not be invoked

to explain

infanticide

in bears.

Resident

male bears

were

infanticidal

in 2 cases documented

during

the breeding

season on the Alaska Peninsula. One of these cases

occurred

in a hunted

area

and the other

in an unhunted

area. Although anecdotal,

these observations

indicated

that resident males, not just immigrant males, were

infanticidal.

Adult females are also sometimes infanti-

cidal (e.g. Hessing and Aumiller 1994).

Comparisons of reproductive intervals between

Alaska and Scandinavia

suggest that if SSI occurs in

brown

bears, it would be more likely to be selected for

in Alaska than in Scandinavia.

In the southern Scan-

dinavian study area, 89% of females separate from

their offspring as yearlings (Swenson et al. 2001a). In

all Alaskan study areas, separation

from offspring as

yearlings was extremely

rare;

separation

usually occur-

red when offspring

were 2 years old (in their

3rd year of

life). If SSI exists in bears, selection for it should be

strongest in populations,

like Alaska, where it would

generate the greatest benefit by hastening estrous in

females with longer

intervals

between

litters.

In contrast,

Swenson (2003) suggested that the longer period of

coexistence between humans and bears in Scandinavia

compared

to North American

may have resulted

in the

evolution of different

behaviors.

Swenson et al. (2001b) suggested

that

the prevalence

of cub mortality in the spring, during the breeding

season, supported

their SSI explanation.

We also found

higher than expected incidence of mortality

of cubs in

the spring

in 3 of our

4 Alaskan

studies.

We suspect

this

Ursus 14(2):130-152 (2003)

HUNTING

EFFECTS

CUB SURVIVORSHIP

* Miller et al. 147

pattern

reflected

relatively high vulnerability

of young,

small, inexperienced cubs following their emergence

from dens. High mortality

rates

for young individuals

common in many mammals (Andrewartha

and Birch

1954, Caughley 1966).

Breeding opportunities

for males are not enhanced

unless the whole litter is ultimately lost. Therefore,

insights

into the likelihood

of the SSI hypothesis

may be

gained by examination of the frequency with which

entire litters are lost in bear populations exposed to

different levels of male removal. From Swenson's

(2001b) data for southern Scandinavia,

we calculated

a rate of whole litter loss of 42% (23 of 55 litters).

Among our study sites, this is most comparable

to the

rate of whole litter loss in unhunted

Katmai

(35%) and

unhunted

Denali (59% of 41 litters; J. Keay, unpub-

lished data).

The two national

parks

in Alaska

as well as

the hunted population

in southern

Scandinavia

all had

higher rates of whole litter loss than in the hunted

populations

at Black Lake and Susitna (14% and 26%,

respectively). These comparisons suggest that hunted

populations

do not universally

have higher

rates

of loss

of entire

litters.

The frequency

with which

entire

litters

are

lost may be

influenced

by the

frequency

of 1-cub

litters. In

the

Alaska

studies, litters of a single cub were most common in

Katmai

(22%

of litters)

and

least common in Black Lake

(9%).

In Denali

and

Susitna,

single cub litters

occurred

12%

and 19% of litters

respectively

(Table

5).

Similarly,

we found no consistent

pattern

among our

hunted

and unhunted

areas of the likelihood that litters

experiencing

loss of >1 cub were completely

lost. Com-

plete loss for such litters

was higher

in the unhunted

area

on the Alaska Peninsula (Katmai compared to Black

Lake) but lower in the unhunted

area in southcentral

Alaska (Denali compared

to Susitna).

The decrease in cub survival

in Sweden following the

intentional increase in male bear killing appeared

consistent

with the SSI explanation

offered

by Swenson

(2003). These recent results appear to support the

suggestion of Swenson (2003) that brown bears in

Europe

may respond

to hunting

pressure

differently

than

North American

brown bears.

Female avoidance of immigrant males

We believe that

Wielgus and Bunnell (1994a) did not

present

persuasive

evidence of increased

male immigra-

tion following hunting

in Kananaskis.

Immigration

was

inferred

based on increased

number

of captures

during

1982-83 compared to 1980-81, although trap-nights

were roughly equal. Carr (1989:7) offered another

explanation

for this difference in capture rates: "The

major

increase

in both

total

and

individual

captures

after

1981 was likely due to the crew's added

experience

and

enhanced

efficiency, along with increased

availability

bait."

We suspect that there is typically a flux of immi-

grant males through both hunted and unhunted

areas

(Glenn and Miller 1980; Reynolds 1997; R. Sellers,

unpublished data for Katmai). Correspondingly,

suggest that avoidance of the best habitats

of the type

posited by Wielgus and Bunnell (2000) should occur in

both hunted and unhunted

populations if it occurs in

either.

In other

studies,

adult

females,

with or without

young,

routinely dominated

subadult

males in using the most

favored sites at concentrated

food resources, such as

salmon streams

or dumps (Horocker 1962, Stonorov

and Stokes 1972, Egbert and Stokes 1976, Bledsoe

1987, Walker 1993, Craighead et al. 1995). Adult

females, including those with cubs, seldom completely

avoided these feeding aggregations

(Sellers and Aumil-

ler 1994). We suspect that adult

females with offspring

foraging at widely dispersed food resources such as

berries (which constituted the prime feeding areas in

Kananaskis)

would be less likely than those at concen-

trated

food sources

to be socially displaced

by males to

the point they are nutritionally disadvantaged. We

believe displacement

of adult

females is even less likely

to be caused by subadult

males.

Infanticide in brown bears

Brown

bears

have some characteristics

consistent,

but

others

that

are

inconsistent,

with the evolution

of SSI by

males. Unlike lions or primates,

for which SSI has been

demonstrated

(Pusey and Packer 1994, Van Noordwijk

and van Schaik 2000), bears do not defend territories

or form family groups; a single male does not domi-

nate a group

of adult

females; infanticidal

males do not

necessarily gain breeding opportunities

to the newly-

available females; and females are polyandrous

during

a single breeding

season. In our view, these character-

istics are impediments

to the evolution of SSI in bears,

although we acknowledge that polyandry has been

suggested as a female counterstrategy

to SSI by males

(van Schaik et al. 2000). Even in lions, where SSI is

well demonstrated

to occur when a dominant

male dies,

male-biased

hunting

may in some cases increase

popu-

lation

growth

rate

if it reduces

takeover

attempts

by non-

harem

males (Greene

et al. 1998).

Predation

and reduced competition may be motives

for some infanticide in brown bears. Bears are large

Ursus 14(2):130-152 (2003)

148 HUNTING EFFECTS ON

CUB

SURVIVORSHIP

* Miller et al.

predatory

carnivores

that will readily kill and consume

other mammals when they can. Adult female brown

bears sometimes

also kill cubs of other

females (Hessing

and Aumiller 1994). This may increase a female's

fitness by reducing

competition

her cubs would other-

wise confront

or through

nutritional

gains by consump-

tion of conspecifics.

The evolutionary history of bears appears to be

one where populations were seldom reduced below

environmental

carrying capacity

by high levels of adult

mortality.

Densities

in excess of carrying

capacities

were

avoided through

high offspring mortality

mediated by

food competition,

maternal

nutritional

constraints,

and

predation by conspecifics. For brown bears, few

predators

other than larger conspecifics can penetrate

a female's formidable ability to defend her cubs. It

would be expected that these evolved mechanisms

and

behaviors

would persist in modem bear populations

densities below carrying

capacity.

Our results are consistent with general ecological

theory

that suggest reduced

recruitment

or survivorship

occurs as populations approach

carrying capacity and

increases occur as populations decline from carrying

capacity densities (Andrewartha and Birch 1954,

Caughley 1977). Because animals

are

removed,

hunting

tends to drive populations

below carrying

capacity.

Cub survivorship: other North American

studies

Like our Susitna studies, high cub survivorship

was

also found in other hunted brown bear populations

interior

Alaska. Survivorship

was 87% (n = 76 cubs) in

the Noatak region of northwestern

Alaska subjected

moderate

male-biased hunting pressure (Ballard et al.

1993). High cub survivorship (72%, n = 137 cubs)

was also found in a heavily hunted populations

in the

northcentral

Alaska range (Reynolds 1997). The hunted

Noatak and northcentral

Alaska Range populations

both had higher cub survivorship

than the unhunted

Denali population (34%). This suggests that the high

survivorship

in heavily hunted Susitna (67%) relative

to Denali was not atypical of comparisons between

hunted and unhunted brown bear populations in

interior

Alaska.

Similar

results

were obtained

in other

Alaskan

studies

of high-density populations sustained by salmon. We

combined data from 4 hunted areas on Kodiak Island

(Smith

and

Van Daele 1991, V. Barnes,

U.S. Geological

Survey [retired], Kodiak, Alaska, USA, unpublished

data). In these high-density salmon-rich areas, lumped

cub survivorship

was 65% (range

= 56-70%, 468 cubs

in 196 litters).

High cub survivorship

(79%, 43 cubs in

24 litters) was also found in a high-density hunted

population

in a salmon-rich

habitat on Admiralty

Island

in southeastern Alaska (Schoen and Beier 1990). The

high cub survivorship

on Kodiak and Admiralty

Islands

indicate that there are additional hunted populations

occurring

in salmon-rich

habitats

that, like Black Lake,

have higher

rates

of cub survivorship

than the unhunted

population

in Katmai

(34%).

Results similar

to ours in Alaska were evident in the

United States-Canada

border

region. Cub survivorship

was slightly higher

in a hunted

population

on the North

Fork of the Flathead

River in southeastern

British Col-

umbia,

Canada

(0.87; Hovey and

McLellan

1996) than

an unhunted

population 100 km southeast

in the Swan

Mountains, Montana (0.79; Mace and Waller 1998).

Unlike our Alaskan national park populations

(Denali

and Katmai),

the unhunted

Swan Mountain

population

was probably below carrying capacity because of

management

kills. Regardless,

this comparison

suggests

that

our

results

showing high cub survivorship

in hunted

areas

relative

to ecologically similar

unhunted

areas

are

not unique

to Alaska.

Throughout

the range of the brown bear in North

America, there are areas with both high and low

survivorship

of cubs in hunted

and

unhunted

conditions.

We suspect that survivorship

of cubs and natality

rates

in bear populations

below carrying

capacity in North

America varies because of factors largely unrelated

the harvest

of males. In populations

at carrying

capacity,

our data indicate reduced cub survivorship

relative to

nearby hunted areas. This appears to be a density-

dependent

response

resulting

from

proximity

to carrying

capacity

in bears.

Management

implications

Bear hunters and some managers of hunted bear

populations

have eagerly

embraced

reports

purporting

show that

hunting

of bears

increases

survival

of young.

More recently,

other

studies

have suggested

that killing

of male bears

resulted

in smaller

litter

sizes or decreased

survivorship

of young. These studies have been em-

braced by groups opposed to bear hunting. When ap-

plied to populations

below carrying

capacity,

we believe

that both of these suggestions are inadequately sup-

ported

by available

data.

The latter

hypotheses

were also

inconsistent

with the results we report

here for hunted

populations in Alaska. In Alaska, increased hunting

pressure did not decrease cub survivorship.

Cub sur-

vivorship

also did not vary subsequent

to years

with and

without

hunting

seasons.

Ursus 14(2):130-152 (2003)

HUNTING EFFECTS

CUB

SURVIVORSHIP

* Miller et al. 149

A different pattern was evident for the unhunted

populations in 2 Alaskan national parks where bear

densities are likely at carrying

capacity. Compared

nearby hunted areas, cub survivorship

was lower in

nearby national parks. This was the reverse of what

would be expected if male-biased hunting disrupted

social structures

leading to increased infanticide. In

Alaska, litter size was not lower in hunted popula-

tions than in unhunted

populations.

These findings are

inconsistent with studies on small populations

of bears

that claimed hunting reduced litter size by restricting

female access to the best foraging

areas.

Managers of exploited bear populations should be

cautious

and explicit about

including density dependent

relationships in their demographic models for bear

populations

below carrying

capacity.

Our

results

support

the inclusion of density-dependent

reductions in cub

survivorship

as bear populations

reach carrying

capac-

ity. Harvests of brown bears should be conservative

because available

techniques

to estimate

population

size

are imprecise and expensive, and because brown bears

have low and variable reproductive

and survivorships

(Miller

1990a). At least in North

American

hunted

popu-

lations below carrying capacity,

inclusion of functional

relationships

between male removal and cub survivor-

ship or litter

size cannot be justified

based on currently

available information. We suspect this is true for very

small as well as larger

populations.

Acknowledgments

We thank V. Barnes for allowing us to cite his

unpublished

cub survivorship

data for Kodiak Island.

J. Swenson made many helpful comments and

clarifications of his data during preparation

of this

manuscript.

We further

appreciate

comments made by

referees J. Swenson, D. Garshelis, and R. Wielgus

during their review of this manuscript

and comments

made by B. McLellan on an early draft. Studies in

southcentral

Alaska were funded by the Alaska Power

Authority (1980-86) and as Federal Aid in Wildlife

Restoration

projects

(most

recently

Grant

W-24-4, Study

4.26). Studies on the Alaska Peninsula

were funded

the National Park Service, the U.S. Fish and Wildlife

Service, the Exxon Valdez

Trustee

Council, the Alaska

Fish and Game Department,

and numerous

Federal

Aid

in Wildlife

Restoration

Projects

(most

recently

Grant W-

24-4, Study 4.0). Many people from state and federal

agencies participated in these projects. Special

recognition

for their work on all these projects

goes to

D. McAllister

and

B. Taylor

(Alaska

Department

of Fish

and Game). Many pilots of fixed-wing aircraft and

helicopters

contributed

to the safety, efficiency, and ac-

curacy

of our studies;

these pilots are

the unsung

heroes

of our studies

in Alaska.

We thank

our

supervisors

at the

Alaska Department

of Fish and Game for their support

of this work and the National Wildlife Federation

for

support during

the preparation

of the manuscript.

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Cannibalism in brown bears (Ursus arctos) is infrequently reported worldwide. This study reports evidence of brown bear cannibalism in northern Hokkaido, Japan. In April 2017, we found a bear scat containing the body parts of a bear cub. We also found a series of tracks (width of the front track: 16 cm) of an adult male bear near the scat, which were likely associated with the excrement. The scat was found at the end of a long hibernation season and the beginning of mating season of brown bears in Hokkaido. The timing suggests that the cannibalism event was a consequence of infanticide by a male bear as part of mating strategy, namely, sexually selected infanticide.

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We analyzed harvest data to test hypotheses that nearly 4 decades of effort to reduce abundance of brown bears (Ursus arctos), black bears (U. americanus) and gray wolves (Canis lupis) in an 60,542 km2 area in south-central Alaska (Game Management Unit [GMU] 13) was positively correlated with moose (Alces alces) harvests in some time-lagged fashion. Predator-reduction efforts were progressively more aggressive over decades (both de facto and officially designated predator control) and did not have clear starting points which complicated our post hoc analyses. We documented no positive correlations (p > 0.05) between harvests of brown and black bears and subsequent moose harvests for any time lag. Moose harvest was negatively correlated with the previous years’ wolf harvest, but the relationship was weak (correlation = −0.33, p < 0.05). Consequently, we reject our hypotheses that harvest of predators was positively correlated with moose harvests. We also observed no differences in mean moose harvests during periods of officially designated wolf control (2005–2020) and a previous period (p > 0.50). We recommend that predator reductions designed to improve hunter harvests of moose be conducted within a research framework that will permit improved interpretations of results and the implementation of an adaptive-management approach to achieve management objectives.

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Large carnivores’ far ranging habits and their requirements for wide areas often led them to move into unprotected lands, making them especially vulnerable to various human threats. Therefore, it is crucial to better understand their mortality characteristics and potential threats so to help guide conservation efforts. Brown bear is a protected species in Iran, however, knowledge on its population structure and causes of mortality are sparse. The main objective of this study was to understand the causes and spatio-temporal patterns of brown bear mortality in Iran. We carried out a systematic survey of internet media sources to answer (1) the mortality of which age and sex group is reported in the media; (2) what are the most common causes of mortality; (3) what are the temporal and spatial patterns of brown bear mortality?. Overall, we found 135 mortalities of brown bears in Iran from 2004-2019. Our findings showed that 84% of mortalities were related to anthropogenic causes and being shot (59%) was the most common cause followed by vehicle collisions (18.7%). Only 2% of reported mortalities were due to natural causes, and no information on the causes of mortality was available for 14%. We further found no differences in the sex distribution of bears killed, but adults (68%) were more commonly killed than subadults (22%); and age was unknown in 9% of mortalities. Most mortalities (75%) were reported in summer and autumn. We found that the number of bear mortality increased with increasing elevation, road density, proportion of forest cover, and that it was higher in areas with a higher proportion of protected areas (PA). However, most reported mortality cases were found outside of PAs. The main takeaway messages from our study are that the conservation of large carnivores in Iran must occur in co-existence with humans in a human-dominated landscape. It is also essential to obtain reliable data on population structure as well as more data on mortality rates and causes. We propose, among other conservation actions, the establishment of a central database for the systematic collection of data on human-carnivore conflicts as well as a compensation scheme for reimbursement of damages by large carnivores.

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Wildlife pedigrees provide insights into ecological and evolutionary processes. DNA obtained from noninvasively collected hair is often used to determine individual identities for pedigrees and other genetic analyses. However, detection rates associated with some noninvasive DNA studies can be relatively low, and genetic data do not provide information on individual birth year. Supplementing hair DNA stations with video cameras should increase the individual detection rate, assuming accurate identification of individuals via video data. Video data can also provide birth year information for individuals captured as young of the year, which can enrich population‐level pedigrees. We placed video cameras at hair stations and combined genetic and video data to reconstruct an age‐specific, population‐level pedigree of wild black bears during 2010–2020. Combining individual birth year with mother–offspring relatedness, we also estimated litter size, interlitter interval, primiparity, and fecundity. We used the Cormack‐Jolly‐Seber model in Program Mark to evaluate the effect of maternal identity on offspring apparent survival. We compared model rankings of apparent survival and parameter estimates based on combined genetic and video data with those based on only genetic data. We observed 42 mother–offspring relationships. Of these, 21 (50%) would not have been detected had we used hair DNA alone. Moreover, video data allowed for the cub and yearling age classes to be determined. Mean annual fecundity was 0.42 (95% CI: 0.27, 0.56). Maternal identity influenced offspring apparent survival, where offspring of one mother experienced significantly lower apparent survival (0.39; SE = 0.15) than that of offspring of four other mothers (0.89–1.00; SE = 0.00–0.06). We video‐documented cub abandonment by the mother whose offspring experienced low apparent survival, indicating individual behaviors (e.g., maternal care) may scale up to affect population‐level parameters (e.g., cub survival). Our findings provide insights into evolutionary processes and are broadly relevant to wildlife ecology and conservation. We installed video cameras at hair stations and combined genetic and video data to reconstruct an age‐specific, population‐level pedigree of wild black bears during 2010–2020. Combining individual birth year with mother‐offpsring relatedness, we also estimated reproductive parameters and evaluated the effect of maternal identity on offspring survival. Maternal identity influenced offspring survival, where offspring of one mother experienced significantly lower apparent survival (0.39; SE = 0.15) than that of offspring of four other mothers (0.89–1.00; SE = 0.00–0.06)

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Monitoring the reproductive characteristics of a species can complement existing conservation strategies by understanding the mechanisms underlying demography. However, methodology to determine important aspects of female reproductive biology is often absent in monitoring programs for large mammals. Protein biomarkers may be a useful tool to detect physiological changes that are indicative of reproductive state. This study aimed to identify protein biomarkers of reproductive status in serum collected from free-ranging female brown bears (Ursus arctos) in Alberta, Canada, from 2001 to 2018. We hypothesized that the expression of proteins related to reproduction in addition to energetics and stress can be used to answer specific management-focused questions: (i) identify when a female is pregnant, (ii) detect if a female is lactating, (iii) determine age of sexual maturity (i.e. primiparity) and (iv) assess female fertility (i.e. reproduction rate). Furthermore, we investigated if silver spoon effects (favourable early life conditions provide fitness benefits through adulthood) could be determined using protein expression. A target panel of 19 proteins with established relationships to physiological function was measured by peptide-based analysis using liquid chromatography and multiple reaction monitoring mass spectrometry and their differential expression was evaluated using a Wilcoxon signed-rank test. We found biomarkers of pregnancy (apolipoprotein B-100 and afamin), lactation (apolipoprotein B-100 and alpha-2-macroglobulin) and sexual maturity (corticosteroid-binding globulin), but there were no statistically significant relationships with protein expression and fertility. The expression of proteins related to reproduction (afamin) and energetics (vitamin-D binding protein) was associated with the nutritional quality of the individual’s present habitat rather than their early life habitat. This study highlights potential biomarkers of reproductive status and provides additional methods for monitoring physiological function in wildlife to inform conservation.

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Bears are the largest terrestrial carnivores, and most bear species can be characterized as opportunistic omnivores. An infrequent foraging tactic for bears is cannibalism, where a bear consumes a conspecific individual, either through scavenging or following intraspecific predation. Although several reports of cannibalism events are known, no attempt has been made so far to gather the available information to analyze for general patterns. We therefore performed a systematic literature review to understand patterns of cannibalism in bears. We documented 39 studies detailing 198 cannibalism events. We only found evidence of cannibalism in 4 of the 8 bear species, with more events reported for polar bears (Ursus maritimus; n = 107, 54.0%) than for all other species combined. Cannibalism was most frequently associated with infanticide (n = 66, 33.3%) and conspecific strife (n = 30, 15.2%), both of which were more frequent among males than females. The most common apparent reason for cannibalism among predators is to increase fitness (i.e., eating a conspecific increases nutrition, whereas killing reduces competition for resources), but is also often linked to sexually selected infanticide in bears. Cannibalism most often appears to be an opportunistic consumption of an available carcass and not directly connected with the primary cause of death. As such, cannibalism in bears may be more casual and opportunistic than a behavior that evolved as a life history strategy.

An apparent case of infanticide in the Asiatic black bear in Japan

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Despite being well-researched in several other bear species, the act of infanticide has yet to be documented in Asiatic black bears (Ursus thibetanus). We captured video footage of an apparent infanticide event in May 2016 using sensor cameras placed outside the winter den of a known female in Nagano Prefecture, Japan. We observed the presence of a known male outside the den, interacting with the female and her offspring. The female ultimately died and her body did not appear to have been consumed by the male bear. From our observations we considered both sexually selected infanticide and nutritional demand as possible motives behind the male's attack.

Analysis of an effort to increase moose calf survivorship by increased hunting of brown bears in south-central Alaska

Article

Full-text available

Jan 1992

The Alces alces population in Game Management Unit 13 increased prior to and during a period of the early 1980s when increased Ursus arctos harvest led to reduced brown bear densities. Because the later portion of the increase in moose populations occurred when bears were being reduced, some observers have inferred that decreased bear densities caused the moose population increase. Analysis does not support this inference. Although calf survival was low primarily because of high predation by brown bears, the authors were unable to detect changes in calf survivorship during the period of bear reduction by hunters. Also, they found no evidence that the bear reduction caused or contributed to the moose population increase. -from Authors

Brown and black bear density estimation in Alaska using radiotelemetry and replicated mark-resight techniques

Article

Full-text available

Jan 1997

Fifteen brown bear (Ursus arctos) and three black bear (U. americanus) density estimates were obtained in Alaska during 1985 through 1992 using 2-9 replicates of capture-mark-resight (CMR) techniques in 17 different areas. Radiotelemetry used to document movement of marked animals into and from search areas eliminated the need to correct density estimates for edge or periphery effects caused by absence of geographic closure. To estimate population size, the authors used a maximum-likelihood estimator modified to accommodate temporary movements of marked animals into and from the search areas. Procedures provided density estimates that were repeatable, were comparable among areas, included estimates of precision, and were more objective than methods historically used to estimate bear abundance. Estimates were obtained within a wide spectrum of habitats and provided a range of Alaskan densities from 10.1 to 551 brown bears (all ages)/1000 km 2 and from 89 to 289 black bears (all ages)/1000 km 2. Brown bear densities were 6-80 times greater in coastal areas where abundant runs of multiple species of salmon (Oncorhynchus spp.) were available to bears than in interior areas.

Population dynamics of brown bears after the Exxon Valdez oil spill

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Full-text available

Jan 1999
URSUS

We estimated survival and reproduction rates of brown bears (Ursus arctos) on the coast of Katmai National Park, Alaska, during 1989-95 to assess effects of the 1989 Exxon Valdez oil spill. Fifteen percent of fecal samples (n = 27) from brown bears captured in 1989 contained hydrocarbons indicative of exposure to crude oil. Females captured in 1989 and 1990 were divided into 2 groups: 12with radiolocations that included oiled coastline and21 that used unoiled areas. Survival rates during 1989-91 were not different (P> 0.90) between females from oiled versus unoiled areas. Based on the assumption that the availability and toxicity of oil was negligible by 1992, we also compared survival rates of both groups during 1989-91 with 1992-95 and observed no difference (P > 0.40). Recruitment rates during 1989-95 were not different (P = 0.12) between females from oiled and unoiled areas. Finite growth rates for the 2 groups suggested both were stable (λ = 1.003 and 1.014, respectively, for bears using oiled and unoiled areas).

Possible Impacts of Hunting on the Grizzly/Brown Bear, a Threatened Species

Article

Full-text available

Jan 1980

Stephen Stringham

Is hunting detrimental to bear populations? Or do harvests stimulate compensatory reproduction and decrease natural mortality among the survivors? When the literature was reviewed to evaluate support for the various sides of this controversy, data were found still inadequate for conclusions to be drawn. At best, available information can aid in distinguishing which additional data are most critical and which hypotheses are most likely to be heuristic. Among six U. arctos populations in North America, those with lowest proportions of adult males had highest reproductive potentials, and vice versa. Likewise, within Yellowstone National Park, there was a strong negative correlation between numbers of adult males during a given year vs. number of offspring. However, those populations with highest reproductive potentials were also in the best habitats. So whether the former relationships were due to (a) effects of adult males on conception and survivorship, or (b) a coincidental product of nutritional differences, must still be tested. For 2 black bear (U. americanus) populations in Idaho, 1 in good habitat which was hunted heavily and the other in poorer habitat that was hunted lightly, higher natality in the former was attributed not to hunting but to better nutrition. When trophy hunting was simulated on a formerly little-exploited population of black bears in Alberta, the natality rate was not obviously altered. Dispersal of a once seasonally aggregated population of grizzly bears was apparently followed by marked increase in cub survival, perhaps because of lowered exposure of cubs to aggression by older bears. However, evidence does not confirm the idea that depletion of mature males substantially increases survivorship of cubs or otherwise offsets losses due to hunting. In fact, under some circumstances, trophy hunting may indirectly increase cub mortality. Aside from this aspect and the possible impacts of inverse culling on gene pools, trophy hunting may be less detrimental to bears than to certain ungulates, where fully-adult males regulate aggression by adolescent males and serve other important social roles.

Observations of intraspecific killing by Brown Bears, Ursus arctos

Article

Jan 1986
Can Field Nat

Reproductive patterns in eutherian mammals: adaptations against infanticide?

Chapter

Nov 2000

Male primates, carnivores and rodents sometimes kill infants that they did not sire. Infanticide by males is a relatively common phenomenon in these groups, but tends to be rare in any given species. Is this behavior pathological or accidental, or does it reflect a conditional reproductive strategy for males in certain circumstances? In this book, case studies and reviews confirm the adaptive nature of infanticide in males in primates, and help to predict which species should be vulnerable to it. Much of the book is devoted to exploring the evolutionary consequences of the threat of infanticide by males for social and reproductive behavior and physiology. Written for graduate students and researchers in animal behavior, behavioral ecology, biological anthropology and social psychology, this book shows that social systems are shaped not only by ecological pressures, but also social pressures such as infanticide risk.

Infanticide in lions: Conse quences and counterstrategies

Article

Jan 1994

Observations of conspecific predation by Brown Bears, Ursus arctos, in Alaska

Article

Jan 1994
Can Field Nat

Impact of increased bear hunting on survivorship of young bears

Article

Jan 1990

Sterling D. Miller

Reviews literature on Ursus arctos and U. americanus supporting a direct relationship between increased hunting (or decreased number of males) and increased survivorship of subadults (reproductively immature bears). Such studies usually have not concluded the existence of a relationship between hunting and increased subadult survival. Evidence from 1 area in Alaska suggests the absence of a relationship between heavy grizzly bear hunting and cub survivorship. -from Author

Implications of sexually selected infanticide for the hunting of large carnivores

Article

Jan 2003

Jon E Swenson

Effects of hunting on brown bear cub survival and litter size in Alaska

Abstract and Figures

Recommended publications

Characteristics of a naturally regulated grizzly bear population: Naturally Regulated Bears

GRIZZLY BEAR POPULATION ECOLOGY AND MONITORING DENALI NATIONAL PARK AND PRESERVE, ALASKA

Black Bear Reproduction and Cub Survivorship in South-Central Alaska

Terrestrial Mammal Study/Population Dynamics of Brown Bears after the Exxon Valdez Oil Spill