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Quantifying Economic Impacts of
Large-Carnivore Depredation on
Bovine Calves
ALBERT P. SOMMERS, Upper Green River Cattle Association, P.O. Box 266, Pinedale, WY 82941, USA
CHARLES C. PRICE, Upper Green River Cattle Association, P.O. Box 375, Daniel, WY 83115, USA
CAT D. URBIGKIT,
1
Sublette County Farm Bureau, P.O. Box 1663, Pinedale, WY 82941, USA
ERIC M. PETERSON, University of Wyoming Cooperative Extension Service, P.O. Box 579, Pinedale, WY 82941, USA
Management and Conservation Article
Quantifying Economic Impacts of
Large-Carnivore Depredation on
Bovine Calves
ALBERT P. SOMMERS, Upper Green River Cattle Association, P.O. Box 266, Pinedale, WY 82941, USA
CHARLES C. PRICE, Upper Green River Cattle Association, P.O. Box 375, Daniel, WY 83115, USA
CAT D. URBIGKIT,
1
Sublette County Farm Bureau, P.O. Box 1663, Pinedale, WY 82941, USA
ERIC M. PETERSON, University of Wyoming Cooperative Extension Service, P.O. Box 579, Pinedale, WY 82941, USA
ABSTRACT We examined and quantified the economic impact of grizzly bear (Ursus arctos) and gray wolf (Canis lupus) depredation on
calves in the Upper Green River Cattle Allotment in western Wyoming, USA, using records of the number of animals grazed and number lost
during 1990–2004. Our analysis indicated that increased calf losses coincided with grizzly bear and gray wolf arrival and population
establishment, with the first confirmed depredation by grizzly bears in 1995 and the first confirmed wolf depredation in 2000. From 1995
through 2004, 29,693 calves grazed on the allotment, and of the 1,332 calves lost to all causes, an estimated 520 calves were lost to grizzly bear
depredation and 177 calves to gray wolf depredation. We examined past and current grizzly and gray wolf compensation programs with respect
to reimbursement of producers for costs associated with large-carnivore depredation. Estimated 1995–2004 uncompensated financial impacts
from grizzly bear and gray wolf calf losses on the allotment were US$222,500. Our analysis suggested equitable compensation factors of 3.8:1
for grizzly bear depredation and 6.3:1 for gray wolf depredation. Inadequate compensation for livestock depredation results in resistance to
large-carnivore recovery programs. Development of compensation programs that fairly reimburse livestock producers for losses is, therefore, a
necessary component of carnivore recovery efforts. Our analysis also suggested that grizzly bear management actions were effectively targeting
livestock-depredating grizzly bears on the allotment.
KEY WORDS cattle, compensation, depredation, gray wolf, grizzly bear, livestock, Wyoming.
Inadequate compensation for livestock losses from depre-
dation causes decreased support for large-carnivore recovery
programs by livestock producers, who often bear much of
the burden of those programs (Anderson et al. 2002).
Existing compensation programs do not fully compensate
livestock producers for their losses. The Upper Green River
cattle allotment of western Wyoming—the largest public
lands grazing allotment in the National Forest system—
provided a setting for a natural experiment examining
increases in depredation levels with expanding predator
populations, complete with baseline information on live-
stock death rates before large-carnivore expansion into the
region.
From 1990 to 2004, the allotment was managed in 4
distinct, multipasture systems, from 5 rider camps by 6 paid
range riders. Three pasture systems were on the west and
north side of the Green River—hereafter, West Side (W
Side)—whereas the fourth pasture system was located on the
east and south side of the river—hereafter, East Side (E
Side)—and was generally rougher and more heavily
timbered than the West Side. Individual ranches placed
their entire herds of cow and calf pairs on either the West
Side or East Side. Herds were subsequently split into
pasture systems without regard to ownership. Cattle
interchange between pasture systems on the East and West
sides of the river was restricted by fencing. In addition,
topographic separation afforded by a wide, unforested river
corridor; a well-traveled forest-system road; and the physical
barrier of the river provided a degree of independence
between these areas.
Grizzly bears (Ursus arctos) and gray wolves (Canis lupus)
entered the allotment from the north as their populations
expanded out of Yellowstone National Park and surround-
ing wilderness areas (Wyoming Game and Fish Department
[WGFD] 2002, Dean et al. 2003). Along the river, in the
allotment, there was an elk (Cervus elaphus) feeding area,
which, with nearby elk calving areas, provided a prey-rich
and carrion-rich environment for grizzly bears as they
emerged from hibernation, whereas gray wolves preyed on
elk in the area during all seasons. Cattle entered the pasture
systems on the west side of the river, usually from 16–30
June, as elk completed calving and began to climb to higher
elevations. Cattle, therefore, moved into areas where
predators were accustomed to taking elk.
In 1993, members of the Upper Green River Cattle
Association (UGRCA) found a calf injured by a grizzly bear,
but it was 2 years later, in 1995, that the first depredation of
cattle by a grizzly bear on the allotment was officially
confirmed. In 2000, the UGRCA experienced the first
officially confirmed wolf depredation. These marked the
first confirmations of grizzly bear or wolf depredation
within the allotment since their presumed extirpation
decades before. During the study period, grizzly and wolf
depredation occurred in all pasture systems. Forage
conditions (i.e., range productivity, poison plants) remained
within normal fluctuations between the period before the
confirmation of large-carnivore presence and afterward,
whereas husbandry practices (e.g., vaccination programs,
pasture management systems, range rider numbers, grazing
period) remained essentially unchanged. More than a decade
of data provide the setting for an examination of how calf-
1
E-mail: catu2@mac.com
Journal of Wildlife Management 74(7):1425–1434; 2010; DOI: 10.2193/2009-070
Sommers et al. NGrizzly and Wolf Depredation 1425
loss trends have changed with large-carnivore population
expansion into the area and to what degree that expansion
has affected ranches grazing cattle in the allotment
monetarily.
Our objectives were to 1) quantify the level of depredation
impacts to calves by grizzly bears and gray wolves, 2)
quantify the uncompensated monetary impact of grizzly and
wolf depredation to producers on this allotment, 3) develop
compensation factors that create compensation equitable to
producers for these depredation losses, and 4) examine the
implications of agency management of predators on calf
losses.
STUDY AREA
The study area was the United States Department of
Agriculture [USDA], Forest Service, Upper Green River
Cattle Allotment (hereafter, allotment) within the Bridger–
Teton National Forest in western Wyoming, USA (Fig. 1).
Grazing permits on the allotment were held by members of
the UGRCA. The allotment was the largest Forest Service
cattle allotment in the United States, permitting 7,565 head
of cattle on approximately 52,609 ha. Ranches using the
allotment, and number of cattle placed on the allotment,
varied annually, depending on climatic and economic
conditions. The study area was located approximately
40 km south of the Yellowstone Grizzly Bear Recovery
Zone in western Wyoming, a designation in effect during
the study period. The allotment had a variety of land covers,
including lodgepole pine (Pinus contorta), quaking aspen
(Populus tremuloides), mountain big sagebrush (Artemisia
tridentata ssp. vaseyana), and shrub-dominated riparian
vegetation. Elevations ranged from 2,330 m to .3,050 m.
METHODS
Level of Depredation
In 1997, the UGRCA surveyed member ranches by written
questionnaire, requesting numbers for calves turned out and
calves lost on the allotment by year. Participation in the
survey was voluntary. Some ranches had discontinued
grazing the allotment, and their data were unavailable.
Because of the sparseness of ranch records before 1990, that
year was chosen as the survey starting point. In 1998, the
survey was expanded to collect annual data from individual
ranches on all cattle losses, not just calf losses. In 1998, the
UGRCA began compiling a list of known cattle deaths.
Nondepredation deaths (e.g., disease, poisoning, lightening)
were categorized by riders and ranchers, whereas confirmed
depredations included only those cattle officially classified as
killed or injured by grizzly bears or gray wolves, as
determined by agency (agencies listed below) personnel.
We have included no injury depredations in this study’s
analysis; thus, all confirmed depredations are cattle that have
been killed by grizzly bears or wolves. We acquired the data
generated by the survey and the list of known cattle deaths
from the UGRCA. We obtained records of confirmed
depredations from the WGFD, the USDA Wildlife
Services (USDA-WS), and the UGRCA. Confirmed
depredation determinations were made by WGFD,
USDA-WS, or United States Fish and Wildlife Service.
We applied linear regression analysis to yearly data to
quantify calf-loss trends and to assess the fit of the data set
to the regression trend line. To determine how changes in
predator presence affected calf-loss rates, we grouped annual
calf-loss data into 3 time-interval treatments: pregrizzly (the
period before confirmed grizzly bear depredation), grizzly-
only (the period containing confirmed grizzly bear depre-
dation but before confirmed wolf depredation), and grizzly–
wolf (the period containing both confirmed grizzly bear and
wolf depredations). These year-groups differed between
West Sides and East Sides, and we examined each side
separately. We tested differences in calf-loss rates for
statistical significance using the general linear module
(GLM) procedure of SAS software (SAS Institute, Cary,
NC). The GLM procedure uses the least-squares method to
fit GLMs. For statistical analysis, we used a random design
with 30 observations defined by year, side of river (i.e., W or
E sides), and treatment. We classified the 3 treatments by
presence of predator species (i.e., pregrizzly, grizzly-only, or
grizzly–wolf). We treated sides of the river as replicates
because the West Side and East Side of the river differed in
location and time of treatment application (i.e., predator
Figure 1. Study area and Upper Green River Cattle Allotment pasture
systems, Wyoming, USA, 1990–2004. The systems lying inside the bend of
the river make up the East Side treatment area.
1426 The Journal of Wildlife Management N74(7)
introduction–presence). Percentage of calves lost was the
dependent variable.
The pregrizzly time interval was the best estimate of the
historic calf-loss rate (e.g., losses from disease, lightening,
poisonous plants) on the allotment in the absence of grizzly
bears and wolves. After depredation was officially con-
firmed, calf losses exceeding the historic calf-loss rate were
attributed to grizzly bear and wolf depredation, including
direct depredation mortalities and mortalities resulting from
the indirect effects of depredation, predominantly stress-
related disease (Anderson et al. 2002, Primm and Murray
2005, Lehmkuhler et al. 2007). Known nondepredation
losses included plant poisoning, lightning strikes, and
disease (A. P. Sommers, UGRCA, unpublished data).
Members of UGRCA did not report an increase in plant
poisoning, lightning strikes, and other deaths not associated
with stress-induced disease during the study period.
We examined the UGRCA’s known-death loss list (e.g.,
dead cattle found by range riders) for West Side calves from
1998 to 2004 to compare known nondepredation calf losses
to grizzly bear–confirmed and wolf-confirmed depredations
to assess whether calf mortality due to disease could be
linked to depredation. We assumed all mortality other than
depredation and stress-induced disease remained constant,
based on consultation with UGRCA members. To make
this examination, we conducted regression analysis to
establish the degree of correlation between nondepredation
losses and depredation losses. We used only West Side data
to calculate this estimate because the East Side rider did not
submit any nondepredation cattle loss data in 1999.
We calculated estimated depredation rates, assuming that
wolf predation was additive to grizzly bear predation. We
used differences in calf-loss rates between depredation
treatments to estimate individual depredation rates by the
2 predator species. We estimated the number of depredation
deaths, by species, by multiplying number of calves placed
on the allotment by the depredation rate of the predator
species. The estimated depredation rate was the estimated
number of calves lost to depredation (i.e., calves killed and
calf mortalities resulting from effects of depredation)
divided by number of calves turned out on the allotment.
We tested the assumption that the grizzly bear depreda-
tion rate we developed for the grizzly-only period remained
the same during the grizzly–wolf treatment by comparing
the number of confirmed calf depredations by grizzly bear
between the grizzly-only and the grizzly–wolf years.
Uncompensated Monetary Impact of Depredation
We assembled previously employed depredation compensa-
tion factors from UGRCA, WGFD, and Defenders of
Wildlife [DOW] records and information to assess whether
there was an uncompensated monetary impact from grizzly
bear and wolf depredation to ranches using the allotment.
Before 1997, WGFD compensated livestock producers only
for confirmed grizzly bear depredations. In 1997, the
WGFD recognized that more calves were killed by grizzly
bears than were found, which was also the conclusion from a
grizzly bear–cattle interaction study (Anderson et al. 1997,
2002). From 1997 to 2004, WGFD paid damage claims
based on a compensation factor periodically altered by
WGFD policy to reflect a growing understanding of cattle–
grizzly bear interaction (Bruscino and Cleveland 2004).
Compensation for livestock depredation by gray wolves is
provided by DOW, a wildlife conservation organization,
which pays full market value for confirmed losses and 50%
of the value for probable losses (DOW 2010). No compen-
sation factor is included in the group’s program to account
for calves lost to wolf depredation but not found. Not all
producers sought compensation for losses from DOW, and
not all producers who sought compensation received it
(C. Urbigkit, Pinedale Online! and Wolf Watch, personal
communication).
We used the product of previously employed compensa-
tion factors and annual confirmed depredations belonging
to reporting ranches to estimate the number of calves for
which reporting ranches could have been compensated
because of grizzly bear and wolf depredation. Assigning a set
value per calf, we calculated the difference between the value
of estimated predator depredations and the estimate of
compensation paid to all reporting ranches in the allotment
to obtain an estimate of the uncompensated monetary
impact of grizzly and wolf depredation on calves.
Equitable Compensation
Past compensation programs used the number of confirmed
depredations, a subset of the total loss, for calculating
compensation. To establish the degree to which the
confirmed calf depredation subset can be a predictor of
total calf depredation, we conducted a regression analysis
pairing confirmed depredation of calves to the percentage of
total calf loss by reporting ranches. A strong correlation
would support development of a calf-depredation compen-
sation program using confirmed depredations as a predictor
of total depredation loss.
We defined the ratio of estimated depredation loss to
confirmed depredation loss as a compensation factor, which
could be employed as an adjustment to the number of
confirmed depredations. The adjusted loss number could be
used to compensate for unconfirmed depredation losses.
To develop a grizzly-depredation compensation factor for
the allotment, addressing unconfirmed depredation of
calves, we examined data from the grizzly-only treatments,
which differed by side of the river (i.e., West Side and East
Side grizzly-only treatments were 1995–1999 and 1998–
2002, respectively). We used only the West Side data
because West Side riders found grizzly bear depredations at
a far greater rate than did East Side riders. We examined
grizzly bear–confirmed depredation rate and estimated
grizzly bear–depredation rate pairs for each side of the river
during grizzly-only treatments to differentiate rider profi-
ciencies and differences in depredation rates between East
Side and West Side. We defined grizzly bear–confirmed and
wolf-confirmed depredation rates on calves as the percent-
age of confirmed depredations of calves belonging to
reporting ranches out of the total calf loss of reporting
ranches from all causes during a given treatment period.
Sommers et al. NGrizzly and Wolf Depredation 1427
Grizzly bear–confirmed and wolf-confirmed depredation
rates are the rates at which riders and ranchers find calves
that have been killed by grizzly bears and wolves in a given
place and time and which have been officially confirmed as a
depredation by agency personnel. Estimated grizzly bear
depredation rate was the estimated number of calves lost to
grizzly bear depredation (i.e., calves killed and calf
mortalities resulting from effects of depredation) divided
by the number of calves turned out on the allotment.
Disparity between species-specific, confirmed depredation
rates indicated either that riders from different areas or
timeframes differed in their proficiency in locating depre-
dations or that depredation rates were different.
In the beginning, range riders (both paid riders and
ranchers) were not experienced at finding or recognizing
livestock depredation. To develop a compensation factor
representing conditions where riders are now proficient at
finding depredations, we assessed rider proficiency at
finding depredations throughout the grizzly-only period.
Based on the comparison of grizzly bear–confirmed
depredation rates and estimated depredation rates, we
excluded the initial 2 years (1995–1996) of data from the
analysis to develop a compensation factor representing
current conditions where riders are proficient at finding
depredations. We calculated the estimated grizzly bear
depredation rate for 1995–1996 by subtracting the historical
loss rate on the West Side from the average calf-loss rate on
both sides for 1995–1996. We used the same method to
calculate the grizzly bear depredation rate for 1997–1999.
We calculated grizzly bear–confirmed depredation rates for
both 1995–1996 and 1997–1999 using the method defined
in preceding paragraphs.
We used calf-loss data from 1997–1999 to develop the
grizzly bear depredation compensation factor. Because not
all ranches submitted data every year, we used only
confirmed grizzly bear depredations from reporting West
Side ranches that provided calf-loss data on a given year. We
excluded confirmed depredations identified as belonging to
nonreporting ranches. When all ranches provided data, we
used all confirmed depredations in our analysis, which
included confirmed depredations of unknown ownership (in
some depredation cases, ranch identifying marks are
consumed or cannot be located).
In developing a wolf depredation compensation factor for
calf losses, we examined data from the grizzly–wolf
treatments, which was 2000–2004 for the West Side and
2003–2004 for the East Side. We used data from both sides
of the river because West Side and East Side riders found
depredations at nearly the same rate. We looked at wolf-
confirmed depredation rates and estimated wolf depredation
rates for each side of the river during grizzly–wolf
treatments. All confirmed wolf depredations of calves,
during 2000–2004, were from ranches who reported calf-
loss data on those years.
Implications of Agency Management
To assess how agency management actions affected the
depredation level of cattle by large carnivores, we obtained
grizzly bear trapping records from the WGFD for the
allotment and compared confirmed grizzly bear calf-
depredation trends with the annual number of grizzly bears
trapped and relocated off the allotment. Wolf management
did not occur on the allotment until 2003, and thus, we did
not analyze it.
RESULTS
Level of Depredation
Calf-loss percentages derived from the survey (Table 1)
demonstrated an increased trend in calf losses and a time lag
in the loss trend on the East Side. Regression analysis
(Fig. 2) indicated nearly identical positive trend slopes and
correlation values (West Side: R
2
50.599; East Side: R
2
5
0.568). Calves accounted for 87% of confirmed depreda-
tions, and most confirmed losses were to reporting ranches
(Table 2). Regression analysis between confirmed calf
depredations and nondepredation calf losses demonstrated
a correlation between nondepredation calf losses and the
level of depredation on the West Side (R
2
50.575; Fig. 3).
Calf losses increased from pregrizzly to grizzly-only to
grizzly–wolf treatments on the West Side and East Side (all:
P,0.001; Table 3; Fig. 2). Average annual estimated grizzly
bear–depredation rate was 1.9% for both the East and West
sides (Table 4). We estimated total calf loss due to grizzly
bear depredation during 1995–2004 to be 520 calves for
reporting ranches (Table 4). We estimated wolf depredation
rate to be 1.4% on the West Side and 1.9% on the East Side.
Total calf loss from wolf depredation (2000–2004) was
estimated at 177 calves for reporting ranches (Table 4).
Uncompensated Monetary Impact of Depredation
We estimated that 520 calves were lost to reporting ranches
from grizzly bear depredation during 1995–2004. Assigning a
2004 market value per calf of US$500, estimated loss to
ranchers in this allotment was US$260,000 (Table 4).
Various grizzly depredation compensation factors used by
WGFD projected compensation for
M
224 calves to reporting
ranches (Table 5). We estimated that WGFD could have
paid US$112,000 in grizzly bear compensation during 1995–
2004, and we estimated the uncompensated monetary impact
of 10 years of grizzly depredation on calves was US$148,000.
We estimated there were 177 calves lost to wolf
depredation from reporting ranches (Table 4), with a value
of US$88,500 at US$500 per calf from 2000 to 2004. Using
the DOW wolf-compensation protocol, reporting ranches
would have been compensated US$14,000 for 28 confirmed
depredations in that period (Table 2). During that 5-year
period, calf losses resulting from wolf depredation cost
reporting ranches US$74,500 in uncompensated monetary
impact. We estimated total uncompensated monetary
impact to reporting ranches from grizzly bear and wolf
depredation on calves in the allotment during 1995–2004 to
be US$222,500.
Equitable Compensation
Our regression analysis indicated a strong relationship (R
2
50.774) between confirmed calf depredations and calf-loss
1428 The Journal of Wildlife Management N74(7)
Table 1. Bovine calf losses on Upper Green River Cattle Allotment and allotment ranches reporting data, Wyoming, USA, 1990–2004.
West side East side Total
Yr
No. of
calves
a
No.
lost
b
%
lost
c
Ranches
No. of
calves
a
No.
lost
b
%
lost
c
Ranches
No. of
calves
a
No.
lost
b
%
lost
c
Ranches
Reporting
d
On
allotment
e
Reporting
d
On
allotment
e
Reporting
d
On
allotment
e
1990 1,215 33 2.7 4 10 333 0 0 1 4 1,548 33 2.1 5 14
1991 1,113 19 1.7 4 9 330 2 0.6 1 4 1,443 21 1.5 5 13
1992 1,630 28 1.7 5 13 690 15 2.2 2 4 2,320 43 1.9 7 17
1993 1,842 72 3.9 6 11 835 15 1.8 3 4 2,677 87 3.2 9 15
1994 2,041 37 1.8 7 10 824 11 1.3 3 4 2,865 48 1.7 10 14
1995 1,823 54 3.0 6 9 792 8 1.0 3 4 2,615 62 2.4 9 13
1996 2,159 94 4.4 7 9 775 18 2.3 3 4 2,934 112 3.8 10 13
1997 2,263 142 6.3 7 10 758 11 1.5 3 4 3,021 153 5.1 10 14
1998 1,722 80 4.6 6 9 1,318 49 3.7 4 4 3,040 129 4.2 10 13
1999 2,106 65 3.1 7 8 811 35 4.3 3 4 2,917 100 3.4 10 12
2000 1,597 56 3.5 6 8 1,259 37 2.9 4 4 2,856 93 3.3 10 12
2001 1,694 65 3.8 6 8 956 26 2.7 3 3 2,650 91 3.4 9 11
2002 2,394 146 6.1 8 8 900 30 3.3 3 3 3,294 176 5.3 11 11
2003 2,376 157 6.6 8 8 806 21 2.6 3 3 3,182 178 5.6 11 11
2004 2,415 176 7.3 8 8 769 62 8.1 3 3 3,184 238 7.5 11 11
Total 28,390 1,224 12,156 340 40,546 1,564
a
No. of calves placed on allotment.
b
No. of calves not returning from the allotment that yr.
c
The % of calf loss occurring during the grazing season.
d
No. of ranches providing information for grazing season.
e
No. of ranches with calves on the allotment.
Sommers et al. NGrizzly and Wolf Depredation 1429
rates to reporting ranches (Fig. 4). During grizzly-only
treatments, grizzly bear–confirmed depredation rate for
reporting ranches on the West Side (1995–1999) and East
Side (1998–2002) was 9.4% (41/435) and 2.3% (4/177),
respectively (Tables 1, 2). The 1995–1996 (excluded
learning period) West Side grizzly bear–confirmed depre-
dation rate for reporting ranches was 2.7% (4/148), and the
grizzly bear depredation rate was 1.3%; the confirmed
grizzly bear depredation rate was 12.9% (37/287), and the
estimated grizzly bear depredation rate was 2.3% for 1997–
1999 (Tables 1, 2). During the grizzly–wolf treatments, the
wolf-confirmed depredation rate on the West Side and East
Side was 4.2% (25/600) and 3.6% (3/83), respectively
(Table 2). The grizzly bear depredation compensation factor
we derived was 3.8:1 (i.e., 3.8 calves lost to grizzly bear
depredation for every calf confirmed as a grizzly depreda-
tion; Table 6). The wolf depredation compensation factor
was 6.3:1 (Tables 2, 4).
Implications of Agency Management
Depredation trends decreased following management ac-
tions by the agency (Fig. 5). Confirmed grizzly bear
depredations increased from 1995–1997. In 1997, one adult
male grizzly bear was relocated off the allotment, and from
1997 to 1998, confirmed grizzly bear depredations subse-
quently decreased, before increasing again in 1999. Then, in
1999, 2 adult male grizzly bears were relocated off the
allotment, and from 1999 to 2001, confirmed grizzly bear
depredations subsequently decreased, before increasing
again during 2001–2003. In both 2003 and 2004, 3 adult
male grizzlies were relocated off the allotment, and from
2003–2004 depredations subsequently decreased.
DISCUSSION
Level of Depredation
A primary monetary impact of grizzly and wolf presence to
ranches using the study area was depredation on calves.
Selective depredation of calves by large carnivores was
consistent with other studies (Murie 1948, Anderson et al.
2002, Lehmkuhler et al. 2007). Data from the UGRCA
provided information regarding depredation on other classes
of cattle (Table 2) and the ongoing survey may provide
additional information to quantify effects of depredation on
yearling and adult cattle.
Our analysis of calf-loss percentages indicated increasing
calf losses that were remarkably similar between East and
West sides and reflected the time lag in expansion of
predator populations across the allotment. The strength and
similarity in trend slopes, and the time lag provided reason
to employ the statistical analysis differentiating presence of
predators as study treatments. The strength in the statistical
difference in calf losses between treatments provided strong
evidence that depredation affects calf loss, allowed differ-
entiation between grizzly bear and wolf depredation, and
supported quantification of losses by predator species.
Figure 2. Upper Green River Cattle Allotment bovine calf-loss trends in
treatment sites, Wyoming, USA, 1990–2004. The East Side regression
exhibits a 5-year time lag, indicating temporal independence. The slope and
correlation are nearly identical.
Table 2. Confirmed bovine-calf and yearling and cow depredations by depredation treatment on the Upper Green River Cattle Allotment, Wyoming, USA,
1990–2004.
Treatment
Total calf depredations
Calf depredations to
reporting ranches
Yearling and cow
depredations
Grizzly bear Wolf Grizzly bear Wolf Grizzly bear Wolf
West side pregrizzly (1990–1994) 0 0 0 0 0 0
West side grizzly-only (1995–1999) 47 0 41 0 5 0
West side grizzly–wolf (2000–2004) 48 25 48 25 4 10
East side pregrizzly (1990–1997) 0 0 0 0 0 0
East side grizzly-only (1998–2002) 5 0 4 0 0 0
East side grizzly–wolf (2003–2004) 0 3 0 3 0 0
Figure 3. Yearly number of confirmed depredations, paired with the
number of known nonpredation losses, of bovine calves, West Side
treatment site, Upper Green River Cattle Allotment, Wyoming, USA,
1998–2004. The relationship suggests stress-induced disease losses are
partly explained by threat of depredation.
1430 The Journal of Wildlife Management N74(7)
Our study indicated that increases in calf-loss rates
exceeding the historic loss rate after confirmed depredations
began were the result of large-carnivore depredation.
Depredation losses included calves killed by depredation
and associated stress-induced mortality. We found a strong
relationship between confirmed calf depredations and
known nondepredation calf losses (Fig. 3; Table 7). Ander-
son et al. (1997) showed the same tendency for nondepre-
dation calf losses to vary with the level of confirmed grizzly
bear–depredated calves on the Blackrock Allotment, which
had terrain similar to our study area. However, the Elk
Ranch Allotment in Anderson et al. (1997) did not show the
same correlation. This strong correlation between confirmed
depredations and nondepredation losses (i.e., mostly disease
losses) suggested that the level of depredation may be a
driving force in stress-induced disease of calves. Anderson et
al. (2002) noted most grizzly bear and wolf depredation of
cattle occurs at night. Cattle that cannot rest at night
become stressed, which may lead to increased risk of disease
(Elenkov and Chrousos 1999, Primm and Murray 2005,
Lehmkuhler et al. 2007). Thus, a portion of total calf loss
was probably due to stress-induced losses, triggered by
depredation. Conversely, diseased calves may have been
prone to depredation, a natural hypothesis not supported by
herd health observations provided by UGRCA members.
Our results were similar to previous depredation studies.
We estimated the grizzly bear depredation rate to be 1.9%
(Table 4), whereas Anderson et al. (1997) data yields a grizzly
bear depredation rate of 1.3%, based on our definition of
estimated grizzly bear depredation rate. Our assumption that
the grizzly bear depredation rate was constant between
treatments was supported by the 47 confirmed grizzly bear
depredations during the grizzly-only treatment compared
with 48 in the grizzly–wolf treatment on the West Side, and
both treatments were 5-year periods (Table 2).
Our analysis produced an estimated wolf depredation rate
of 1.4% on the West Side and 1.9% on the East Side
(Table 4), whereas a wolf–cattle interaction study in Idaho,
USA, estimated the wolf depredation rate to be 1.2% during
that 2-year study (Oakleaf et al. 2003). The grizzly bear and
wolf depredation rates in Anderson et al. (2002) and Oakleaf
et al. (2003) were based on depredated calves found with
telemetry. Our grizzly bear and wolf depredation rates were
slightly larger than rates from these other studies, perhaps
because our depredation rates included calves killed by
depredation and deaths from depredation-influenced disease.
Table 4. Summary of grizzly bear and wolf depredation calculations,
Upper Green River Cattle Allotment, Wyoming, USA, 1995–2004.
Calculation variable
West
side
East
side
Grizzly-only treatment, no. of calves
turned out (A) 10,073 5,244
% calf loss (B) 4.3 3.4
% historic calf-loss rate (C) 2.4 1.5
% grizzly bear–depredation rate (D5B2C) 1.9 1.9
Estimated grizzly bear–depredation loss of
calves (A3D) 191 100
Grizzly–wolf treatment, no. of calves turned
out (E) 10,476 1,575
Estimated grizzly bear–depredation loss of
calves (E3D) 199 30
Grizzly–wolf treatment, no. of calves turned
out (E) 10,476 1,575
% calf loss (F) 5.7 5.3
% wolf-depredation rate (G5F2C2D) 1.4 1.9
Estimated wolf depredation loss of calves
(E3G) 147 30
Table 5. Estimated compensation by Wyoming Game and Fish
Department for grizzly bear–depredated calves to reporting ranches on
Upper Green River Cattle Allotment, Wyoming, USA, 1996–2004.
Yr
Confirmed
grizzly bear
depredations
Compensation
factor employed
Compensation
(No. of calves)
1996 4 1.00 4.0
1997 19 1.35 25.7
1998 12 1.67 20.0
1999 8 1.67 13.4
2000 6 1.67 10.1
2001 2 1.67 3.3
2002 11 3.50 38.5
2003 23 3.50 80.5
2004 8 3.50 28.0
Total 100 224
Figure 4. Percentages of ranches in Upper Green River Cattle Allotment
reporting yearly bovine calf-loss, paired with confirmed depredations,
Wyoming, USA, 1993–2004. The presence of a strong relationship supports
the development of a compensation factor based on confirmed depredations.
Table 3. Summary of average annual bovine-calf–loss rates by depredation
treatment on Upper Green River Cattle Allotment, Wyoming, USA, 1990–
1994.
Treatment intervals
No. of
calves No. lost
%
lost
a
West side pregrizzly (1990–1994) 7,841 189 2.4
West side grizzly-only (1995–1999) 10,073 435 4.3
West side grizzly–wolf (2000–2004) 10,476 600 5.7
East side pregrizzly bear (1990–1997) 5,337 80 1.5
East side grizzly-only (1998–2002) 5,244 177 3.4
East side grizzly–wolf (2003–2004) 1,575 83 5.3
Combined pregrizzly bear 13,178 269 2.0 A
Combined grizzly-only 15,317 612 4.0 B
Combined grizzly–wolf 12,051 683 5.7 C
a
Percentages with the same letters do not differ significantly at P,
0.001.
Sommers et al. NGrizzly and Wolf Depredation 1431
The West Side historic (1990–1994) calf-loss rate was
higher than that on the East Side (Table 3), possibly
because of the presence of grizzly bears on the West Side
before 1995. West Side ranchers found what was believed to
be a calf mauled by a bear in 1993, which suggested there
was some level of grizzly bear depredation before 1994.
The calf-loss rates we found are consistent with those found
in similar studies (Table 3). A cattle mortality study in
Canada found a 2.02% calf-loss rate on summer-grazing
pastures, where depredation was uncommon, and a 5.7% calf-
loss rate on pastures with grizzly bear and wolf depredation
(Bjorge 1983). Oakleaf et al. (2003) estimated that the
nondepredation calf-death rate was 2.3% in Idaho. Analysis
of data from a Wyoming grizzly bear–cattle interaction study,
based on calf-loss records, produced an average annual calf-
loss rate of 2.5%, before confirmed grizzly bear depredation,
and an average annual calf-loss rate of 6.2%, after grizzly bear
depredation was discovered (Anderson et al. 2002).
Uncompensated Monetary Impact of Depredation
The Western Wyoming United States Forest Service
Grazing Model for a 610–brood-cow ranch generated
US$27,822 per year of projected profit for a Bridger–Teton
National Forest ranch operation (Taylor et al. 2007). Using
this benchmark, the estimated 1995–2004 monetary impact
of uncompensated predation on the Upper Green River
Cattle Allotment is roughly equivalent to the profit expected
from 493 cows per year, 16.6% of the allotment’s average
herd. Our study did not address the lost potential income
from calves that would otherwise be retained into yearling,
feeding, or breeding herd enterprises.
Equitable Compensation
Equitable compensation factors should account for the
variables unique to a particular allotment, including
topography, predator abundance, vegetation characteristics,
and herding intensity. Historically, WGFD and DOW used
confirmed depredations as the basis for compensation paid
to ranchers for livestock losses resulting from large-carnivore
depredation. Agency use of compensation factors acknowl-
edges that not all depredations are found (Bruscino and
Cleveland 2004). The disparity between compensation
factors used to compensate ranchers on the Upper Green
River Allotment during our study period and compensation
factors we developed suggest that those compensation
factors insufficiently provided for equitable compensation.
Our 6.3:1 wolf depredation compensation factor for the
allotment was conservative compared with the 8:1 ratio of
calves killed by wolves to calves found killed by wolves
estimated in Idaho (Oakleaf et al. 2003). Our wolf
depredation compensation factor was higher than the grizzly
bear depredation compensation factor, likely because wolf
depredations are harder to find and confirm than grizzly
bear depredations (Bjorge and Gunson 1985).
We determined whether confirmed depredations were a
reliable predictor of actual depredation loss on the allotment
to verify whether confirmed depredations can be used as a
basis for an equitable compensation program, as confirming
a depredation is a difficult and subjective process. If
depredations were not found and confirmed in proportion-
ate numbers, then confirmed depredations may not track
actual depredation losses on the allotment. Absence of a
Figure 5. Grizzly bear management action and West Side treatment area’s
confirmed depredations, Upper Green River Cattle Allotment, Wyoming,
USA, 1993–2004. Aggressive management of depredating grizzly bears
reduces subsequent calf depredation.
Table 7. Calf losses found and categorized by manner of death on the West Side of the Upper Green River Cattle Allotment, Wyoming, USA, 1998–2004.
Yr Total loss Nondepredation loss
Confirmed grizzly bear
depredations
Confirmed wolf
depredations
Total confirmed
depredations
1998 35 25 10 0 10
1999 48 34 14 0 14
2000 33 28 4 1 5
2001 18 16 2 0 2
2002 41 27 11 3 14
2003 67 39 23 5 28
2004 91 67 8 16 24
Total 333 236 72 25 97
Table 6. Grizzly bear–depredation compensation factor summary for
reporting West Side ranches, Upper Green River Cattle Allotment,
Wyoming, USA, 1997–1999.
Parameter Calves
Calves turned out 6,091
Total calf loss (A) 287
Historic calf loss (B) 146
Depredation loss above historical loss (C5A2B) 141
Confirmed grizzly bear depredations 37
Ratio of calves lost to depredation:confirmed
depredation 5grizzly bear compensation factor 3.8:1
1432 The Journal of Wildlife Management N74(7)
correlation between calf loss and confirmed depredations
(i.e., depredation level) would suggest some other reason
(e.g., increased cattle rustling) for calf-loss variations or
insufficient sampling. However, confirmed depredations
and calf loss were correlated, suggesting confirmed depre-
dations were an accurate predictor of calf loss, and thus
depredation loss, and supported development of a compen-
sation factor.
There is no disparity between East Side and West Side
estimated grizzly bear depredation rates, meaning the level
of depredation was similar on both sides. However, because
there is disparity between East Side and West Side grizzly
bear–confirmed depredation rates, there is evidence of
variability in riders locating depredations. We excluded
East Side grizzly bear depredation data (i.e., confirmed
depredations) to develop a compensation factor that
represented current conditions, where rider proficiency in
finding depredations was higher than exhibited by the East
Side rider during that period. However, we estimated calf-
depredation losses (Table 4) on the East Side because there
were significantly higher calf losses from the pregrizzly to
the grizzly-only to the grizzly–wolf treatment years. A
heavily timbered, rough area, like the East Side, complicated
locating both natural and depredation deaths of cattle and
may warrant a different grizzly bear–depredation compen-
sation factor in the future.
We hypothesized that, initially, range riders and ranchers
were not efficient at finding or recognizing livestock
depredation and that, after a learning period, West Side
riders achieved and maintained greater proficiency in
recognizing depredation. We eliminated the 1995–1996
West Side data from development of a grizzly bear
depredation compensation factor because, as the estimated
grizzly bear–depredation rate nearly doubled, the grizzly
bear–confirmed depredation rate increased 5-fold from the
period 1995–1996 to the period 1997–1999. Therefore, we
excluded the initial 2-year period of rider training to develop
a compensation factor representing current conditions. We
used calf-loss data from the 1997–1999 period to develop
the grizzly bear–depredation compensation factor.
Compensation factors we developed should equitably
compensate ranches using the allotment for direct impacts
of grizzly bear and wolf depredation. However, there exist
indirect impacts from grizzly bear and wolf range expansion
into the allotment. For instance, cattle subject to depreda-
tion by large carnivores were reported to breach fences to
escape, resulting in cattle occupying areas out of rotation
and complicating cattle management. There are areas,
especially small open meadows in the timber, where cattle
will not stay, resulting in loss of available forage because of
the presence of predators (A. P. Sommers, personal
communication). The UGRCA cited instances where
depredation-induced disturbances forced the UGRCA to
rotate cattle to the next pasture earlier than scheduled or to
remove cattle from the allotment early. Loss of summer
forage and increased forage pressures on private ranch lands,
which previously would have been allocated to other uses,
may precipitate reduction in cattle numbers, thus reducing
economic efficiency. Examining these indirect impacts was
beyond the scope of our study, but future research should
seek to verify and quantify indirect impacts of depredation.
Implications of Agency Management
Grizzly bear calf–depredations decreased in years following
relocation or removal of depredating adult male grizzly bears
off the allotment (Fig. 5), indicating that calf-loss rates were
tied to the level of grizzly bear depredation and management
actions by WGFD. This decrease in calf depredations
suggests WGFD was effective in identifying and trapping
grizzly bears responsible for calf depredation. Management
(i.e., relocation or removal) of adult male grizzly bears
seemed to decrease depredation levels but did not adversely
affect grizzly bear populations (Anderson et al. 2002,
Moody et al. 2005).
MANAGEMENT IMPLICATIONS
Introduction and expansion of populations of large preda-
tors (e.g., grizzly bears and wolves) into grazing allotments
creates a monetary impact on livestock operators because of
increased calf losses from grizzly bear and wolf depredation.
Evidence suggests that aggressive management of predating
grizzly bears reduces subsequent depredation (Anderson et
al. 2002). Increased management requirements on allot-
ments because of large-carnivore depredation create in-
creased economic burdens on livestock permittees (Bruscino
and Cleveland 2004).
Whereas species recovery is in the public’s interest, a
disproportionate share of the cost of predator recovery
programs falls upon a few individuals. Adequate compen-
sation programs are an efficient means to acknowledge this
responsibility and to fairly apportion costs and benefits.
ACKNOWLEDGMENTS
Ranchers were responsible for collecting data, conducting
the analysis, and writing the research report. We appreciate
the efforts of M. Bruscino, Wyoming Game and Fish
Department Bear Management Officer, and M. Smith,
University of Wyoming Department of Renewable Re-
sources. We also thank C. Ellison, University of Wyoming
Department of Renewable Resources, for providing a
statistical analysis of Table 3 data. We would like to thank
numerous other reviewers, including B. Rashford and J.
Knight, as well as UGRCA.
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1434 The Journal of Wildlife Management N74(7)
