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Research Article
Changing Migratory Patterns in the
Jackson Elk Herd
ERIC K. COLE,
1,
U.S. Fish and Wildlife Service, National Elk Refuge, PO Box 510, Jackson, WY 83001, USA
AARON M. FOLEY,
U.S. Geological Survey, Northern Rocky Mountain Science Center, 2327 University Way, Suite 2, Bozeman, MT 59715, USA
JEFFREY M. WARREN, U.S. Fish and Wildlife Service, Red Rock Lakes NWR, 27650B South Valley Rd., Lima, MT 59739, USA
BRUCE L. SMITH,
2
U.S. Fish and Wildlife Service, National Elk Refuge, PO Box 510, Jackson, WY 83001, USA
SARAH R. DEWEY, National Park Service, Grand Teton National Park, PO Drawer 170, Moose, WY 83012, USA
DOUGLAS G. BRIMEYER, Wyoming Game and Fish Department, PO Box 67, Jackson, WY 83001, USA
W. SUE FAIRBANKS,
3
Department of Natural Resource Ecology and Management, Iowa State University, 339 Science Hall II, Ames, IA 50011,
USA
HALL SAWYER, Western Ecosystems Technology, Inc., 200 South 2nd Street, Laramie, WY 82001, USA
PAUL C. CROSS, U.S. Geological Survey, Northern Rocky Mountain Science Center, 2327 University Way, Suite 2, Bozeman, MT 59715, USA
ABSTRACT Migratory behavior in ungulates has declined globally and understanding the causative factors
(environmental change vs. human mediated) is needed to formulate effective management strategies. In the
Jackson elk herd of northwest Wyoming, demographic differences between summer elk (Cervus elaphus)
population segments have led to changes in migratory patterns over a 35-year time period. The proportion of
short-distance migrants (SDM) has increased and the proportion of long-distance migrants (LDM) has
concurrently declined. The probability of winter-captured elk on the National Elk Refuge being LDM
decreased from 0.99 (95% CI ¼0.97–1.00) to 0.59 (95% CI ¼0.47–0.70) from 1978 to 2012. We tested
4 hypotheses that could contribute toward the decline in the LDM segment: behavioral switching from
LDM to SDM, differential survival, harvest availability, and calf recruitment. Switching rates from LDM to
SDM were very low (0.2% each elk-year). Survival rates were similar between LDM and SDM, although
harvest availability was relatively low for SDM that tended to use areas close to human development during
the hunting season. Average summer calf/cow ratios of LDM declined from 42 to 23 calves per 100 cows
from 1978–1984 to 2006–2012. Further, during 2006–2012, LDM summer calf/cow ratios were less than
half of SDM (23 vs. 47 calves per 100 cows). Our data suggest recruitment is the driving factor behind the
declining proportion of LDM in this region. Effectiveness of altering harvest management strategies to
conserve the LDM portion of the Jackson elk herd may be limited. Published 2015. This article is a U.S.
Government work and is in the public domain in the USA.
KEY WORDS Cervus elaphus, elk, Greater Yellowstone Ecosystem, migration, migratory distance, National Elk
Refuge, predation, recruitment, summer range, survival.
Migration is a phenomenon exhibited by numerous genera
and usually is a behavioral response to distribution of
resources (Milner-Gulland et al. 2011). Ungulate migration
is an adaptive behavioral strategy to obtain more nutritious
forage resources and to avoid predation (McCullough 1985,
Fryxell and Sinclair 1988, Bergerud et al. 1990). Some taxa
have altered migratory behavior for a variety of reasons
including, but not limited to, anthropogenic activities,
changing climate, and predation risk (Caccamise et al. 2000,
Mbaiwa and Mbaiwa 2006, Wilcove and Wikelski 2008).
Numerous partially migratory elk (Cervus elaphus) popula-
tions occur throughout western North America (Martinka
1969, Rudd et al. 1983, Woods 1991, Haggerty and Travis
2006, Robinson et al. 2010). Some advantages of migration
may have been lost over time as climatic patterns have
changed. For instance, Middleton et al. (2013a) suggested
that elk migrating to high elevation areas in Yellowstone
National Park (NP) were subject to drought induced changes
in forage quality that resulted in lower fat reserves, lower
pregnancy rates, and lower recruitment. Additionally,
Hebblewhite and Merrill (2011) and Middleton et al.
(2013a) found that migratory elk were subject to higher
predation rates than non-migratory elk, perhaps because
Received: 11 September 2014; Accepted: 19 April 2015
Published: 18 June 2015
1
E-mail: eric_cole@fws.gov
2
Present Address: 44 Duncan District Road, Sheridan, MT 59749.
3
Present Address: Department of Natural Resource Ecology and
Management, Oklahoma State University, 564 Agricultural Hall,
Stillwater, Oklahoma.
Eric K. Cole and Aaron M. Foley contributed equally to this work.
The Journal of Wildlife Management 79(6):877–886; 2015; DOI: 10.1002/jwmg.917
Cole et al. Elk Migratory Changes 877
large predators like bears (Ursus spp.), wolves (Canis lupus),
and mountain lions (Puma concolor) are easier to conserve in
areas more distant from human habitation, which, in the
United States, also tend to be higher elevation regions. The
differential exposure to limiting factors between non-
migratory and migratory elk groups is a concern because
of the ecological and wildlife management consequences
associated with conserving traditional migration behavior
(Berger 2004, Wilcove and Wikelski 2008).
Many species of waterfowl, salmonids, and ungulates have
mixed migration strategies (Allendorf et al. 2008). Managers
often try to preserve the migratory behaviors of these species
by adjusting hunting and fishing regulations in different
regions, but this is difficult when migratory and sedentary
segments of a population use a shared seasonal range during
harvest seasons (Tacha et al. 1984, Caccamise et al. 2000,
Wilson 2002, Reiss et al. 2009). Harvest via commercial
fishing and recreational hunting can strongly influence
annual population sizes (Solberg et al. 1999, Levin et al.
2006, Allendorf et al. 2008). Thus, understanding how
subpopulations differ in use of space is important for
quantifying the potential impact of harvest activities on each
subpopulation (Mauritzen et al. 2002). For instance, resident
Canada goose (Branta canadensis) populations are commonly
hunted prior to and after migration to minimize harvest of
migratory geese while maximizing harvest of residents
(Caccamise et al. 2000). Surprisingly, little research has
explored whether selective harvest could be partially driving
different population growth trajectories between elk that
display different migratory behavior (Smith 2007). For
example, in their study of migratory and resident elk east of
Yellowstone NP, Middleton et al. (2013a) did not consider
differential harvest mortality between migratory and resident
elk. Understanding whether differential harvest exists, and
what the consequences may be, is critical for managing
partially migratory populations.
The National Elk Refuge (hereafter termed the Refuge)
hosts one of the world’s largest concentrations of wintering
elk, with an average of 7,300 elk occupying the Refuge from
November to May each year, representing approximately
65% of the Jackson elk herd. Management of the Refuge and
Jackson elk herd has been the subject of intense scrutiny and
debate (Boyce 1989, U.S. Fish and Wildlife Service
[USFWS] and National Park Service [NPS] 2007, Smith
2011). Elk receive supplemental feed on the Refuge operated
by the USFWS and on 3 other feedgrounds northeast of
the Refuge operated by the Wyoming Game and Fish
Department (WGFD). Supplemental feeding has been
employed in all but 9 winters on the Refuge since 1912. For
the period of 1995–2014, elk were fed pelletized alfalfa at a
mean daily rate of 3.6 kg per elk an average of 66 days a year.
Supplemental winter feeding has minimized elk winter
mortality, enhanced elk hunting opportunities, and reduced
elk damage on private lands via maintaining elk on
feedgrounds (Boyce 1989). However, supplemental feeding
concentrates high numbers of elk in the same sites each
winter, and elk density commonly exceeds 150 elk/km
2
on
the Refuge (E. Cole, USFWS, unpublished data). Such
densities have resulted in loss of woody plant communities
and bird habitat (Smith et al. 2004, Anderson 2007) and
increased the prevalence of density-dependent diseases
(Murie 1951, Franson and Smith 1988, Samuel et al.
1991, Herriges et al. 1992, Smith and Roffe 1997).
Migrations of elk from the Refuge to summer ranges in
Grand Teton NP, the Gros Ventre Mountains, Teton
Wilderness, and Yellowstone NP have been well docu-
mented (Anderson 1958, Cole 1969, Craighead et al. 1972,
Boyce 1989, Smith and Robbins 1994). Boyce (1989)
suggested that approximately 35% of the Jackson elk herd
occupied summer ranges in southern Yellowstone NP in
1964, and Smith and Robbins (1994) estimated that 31% of
cow elk captured on the Refuge between 1978 and 1982
summered in Yellowstone NP. In contrast, only <2% of elk
sampled by Smith and Robbins (1994) summered between
Wilson and Moose, Wyoming in southern Grand Teton NP
(Fig. 1). Anecdotal observations by wildlife managers,
hunters, and others suggested that the proportion of elk
occupying the Wilson to Moose, Wyoming area had
increased dramatically, whereas the proportion of elk that
summer elsewhere (e.g., Yellowstone NP, Teton Wilderness,
and Grand Teton NP; Fig. 1) had declined over 3 decades.
We examined the changes in proportion of these elk captured
in winter on the Refuge from 1978 to 2012 and evaluated the
possible ecological and management factors that could be
responsible for the observed changes. We then discuss the
implications of these findings to meeting the Refuge and
Jackson elk herd population objectives and the management
strategies for conserving declining migratory populations
where recreational harvest occurs.
STUDY AREA
We conducted this study in and around the Jackson elk herd
unit (approximately 8,000 km
2
) in northwest Wyoming,
which included the Refuge, Grand Teton NP, Bridger-
Teton National Forest (NF), and southern Yellowstone NP
(Fig. 1). Herd unit boundaries were delineated by the
WGFD to encompass a distinct group of elk from which
there would be <10% annual interchange with surrounding
elk herds (Gasson 1987). Elevations ranged from a low of
1,850 m in the Snake River flood plain to almost 4,200 m in
the Teton Range. Boyce (1989) and Smith and Robbins
(1994) described the herd unit’s boundaries, geological
features, and plant communities. Summer ranges of the elk
occupied a wide range of topographic and vegetative features,
from residential subdivisions and irrigated pasture, sagebrush
(Artemesia spp.) grasslands, forests of lodgepole pine (Pinus
contorta), and subalpine fir (Abies lasiocarpa), to alpine tundra
in the highest elevations of the study area. The 98-km
2
Refuge was established in 1912 with a primary purpose of
providing winter range for the Jackson elk herd. Boyce
(1989), Smith and Robbins (1994), Smith et al. (2004), and
Smith (2011) provided detailed descriptions of the history
and management of the Jackson elk herd.
Elk hunting occurred throughout the study period, with
season length, sex restrictions, and areas open to hunting
varying by year. The Yellowstone NP was closed to hunting,
878 The Journal of Wildlife Management 79(6)
but elk that summered there were subject to hunting during
migration to winter range. In Grand Teton NP, elk were
subject to harvest in areas east of the Snake River under
Public Law 81-787. During the 1970s, elk management was
focused on maximizing hunter opportunity to control elk
populations in northern Grand Teton NP, and the Teton
Wilderness. This was accomplished by extending hunting
seasons into November for unlimited general license as well
as limited quota license opportunities. Hunting was allowed
on the Refuge and hunting opportunities on private lands
south of Grand Teton NP were limited because of housing
density, subdivision covenants, and land access. Despite
these limitations, WGFD has worked with landowners to
maximize elk harvest on private lands adjacent to the Refuge.
In recent years, WGFD has designed hunting seasons to
reduce harvest of migratory elk from Yellowstone NP and
Teton Wilderness through bull-only seasons and reduced
season length, quotas, and license types in areas east of the
Refuge.
METHODS
Capture and Collars
We used radio-collar data of female elk from 3 distinct
periods of study on the Jackson elk herd conducted by Grand
Teton NP, Western Ecosystems Technology, Inc. (WEST),
the Refuge (Smith and Robbins 1994, Smith 2007, E. Cole,
unpublished data), Iowa State University (ISU; Barbknecht
et al. 2011), and WGFD. Winter (Jan–Mar) captures were
on the Refuge, Buffalo Valley within and outside of Grand
Teton NP, and 3 state feedgrounds in the Gros Ventre
drainage (Alkali, South Park, and Patrol Cabin; Table 1,
Fig. 1). Summer elk captures (Jul) were conducted within
Grand Teton NP and Teton Wilderness Area (Table 1,
Fig. 1). Capture activities were approved by WGFD
(Chapter 33 permits #394 and #624) and ISU Animal
Care and Use Committee (Protocol #8-05-5962).
Telemetry data were divided into 3 7-year periods to
correspond with the independent studies comprising the data
used here. The first period (P1) was 1978–1984, period 2
(P2) was 1994–2000, and period 3 (P3) was 2006–2012. Elk
captured during P1 and P2 were fitted with very high
frequency (VHF) radio collars (U.S. Department of
Agriculture Denver Wildlife Research Center and Telonics,
Inc., Mesa, AZ) and monitored via aerial and ground
telemetry. Elk captured during P3 were fitted with global
positioning system (GPS) radio collars (Lotek Inc.,
Newmarket, ON, Canada; Advanced Telemetry Systems,
Inc., Isanti, MN; and Telonics, Inc.). Average number of
locations per elk was 55 (range ¼6–156) and 46 (range ¼5–
103) during P1 and P2, respectively. Elk with GPS collars
during P3 had varying fix rates (range ¼2–24 hr) that
Figure 1. Elk capture sites, feedgrounds (triangles), and National Parks within the Jackson elk herd study area in northwestern Wyoming, USA (left) and hunt
areas where female elk were legal for harvest (right). Note that hunt areas 75 and 79 are within Grand Teton National Park. The close-up image (bottom)
depicts the summer range of short-distance migratory (SDM) elk south of the dotted line; black areas within hunt area 78 were privately owned and light gray
areas were National Forest lands. Note the National Elk Refuge is hunt area 77.
Cole et al. Elk Migratory Changes 879
resulted in considerably more locations per individual (mean
number of locations per elk ¼1,004, range ¼69–4,416).
Only adult females were collared except during P2 when all
captured females were 1-year-old.
Summer Range Classification
The summer range between Wilson and Moose, Wyoming is
only 8–10 km west and northwest of the Refuge, and we
defined elk that summered in this area as short-distance
migratory elk (SDM). We did not classify these elk as
resident elk (Hebblewhite and Merrill 2011, Middleton et al.
2013a) because these elk do not reside on winter ranges year-
round. The SDM occupying the area between the towns of
Wilson and Moose, Wyoming (Fig. 1) are distinct from
long-distance migratory elk (LDM) because of 1) shorter
migratory distance between summer range and the Refuge,
2) greater anthropogenic influences such as housing
development and agricultural activity, and 3) relatively late
seasonal migration to winter range (Fig. S1, available online
at www.onlinelibrary.wiley.com). Three elk that summered
within 8–10 km northeast of the Refuge in the Bridger-
Teton NF were considered LDM elk in our analyses because
they did not meet criteria 2 and 3 in our definition of SDM.
We classified elk as LDM or SDM based on the location of
summer-range centroids relative to the SDM–LDM
boundary (Fig. 1). We estimated summer home ranges
using locations obtained 1 July to 30 September, except for 2
elk that were still migrating after 1 July. For these elk, we
used locations after the net squared displacement reached an
asymptote (when the distance between the winter range and
the elk became consistent). We used minimum convex
polygons (MCP; Worton 1987) to identify centroid
locations for each individual-year summer ranges. Because
the VHF-collared elk during P1 and P2 had relatively fewer
locations compared to GPS radio-collared elk, we randomly
selected X locations per GPS elk with the caveat that X was
within the range of VHF locations (n¼6–156) with the
intention to reflect intensity of data acquisition during P1
and P2.
Proportion Migratory
We tested for a declining probability of a marked female elk
on the Refuge being LDM using generalized linear models
in R 3.0.3 (R Development Core Team 2005), binomially-
distributed errors, and a logit link. We assessed model
goodness-of-fit assuming a x
2
distribution for the estimated
deviance with n–k degrees of freedom, where nis the sample
size and kis the number of estimated parameters (Neter et al.
1996). We calculated standard errors using the delta method
(Oehlert 1992).
We used radio-collar data from all elk captured on the
Refuge to assess the frequency of elk that switched from
LDM to SDM. We divided the number of switches from
SDM to LDM (or vice versa) by the total number of elk-
years. To further evaluate whether movement behaviors have
changed over time, we computed average distance between
each summer home-range centroid of elk captured on the
Refuge and the Refuge centroid during P2 and P3.
Behavioral switching may be a function of distance because
elk that summer on the periphery of the SDM–LDM
boundary area may be more likely to become SDM relative to
elk that summer elsewhere (e.g., Yellowstone NP). We used
a subset of individuals from P3 to graphically test for
monotonically declining distance between consecutive
summer centroids per individual and the Refuge. Lastly,
we obtained the switching rate and estimated elk population
sizes for both LDM and SDM to model how many years of
consistent switching would result in the current proportion
of LDM to SDM assuming constant rates of birth, death,
emigration, and immigration. The number of SDM or LDM
elk in year tare SDM
tþ1
¼SDM
t
(aþ1) and LDM
tþ1
¼
(1 a)LDM
t
, where ais the net proportion that switched
from LDM to SDM.
We used radio-telemetry data from all female elk from all 3
periods to estimate annual survival of LDM and SDM. We
defined an elk-year as 1 January to 31 December. We chose 1
January as our start date because the earliest captured elk
occurred on 17 January. The first study period concluded on
21 November 1984, the final year of P1; we ended P2 and P3
on the same day of their final years. We right censored
individuals that switched from LDM to SDM, or vice versa,
and created a new encounter history with the new status
starting the year switching occurred. We used Kaplan–Meier
staggered entry survival analysis (Heisey and Patterson 2006)
via R package wild1 (Sargeant 2011).
For the harvest availability analyses, we limited our scope to
P3 when GPS radio-collar data were available. We compared
proportional use of hunt areas among elk captured on
different sites (e.g., Refuge, Buffalo Valley, etc.) and did not
detect differential proportional use. Habitat-induced bias
(Frair et al. 2004, Nielson et al. 2009) due to different terrain
Table 1. Years of elk capture, study publication or agency, capture methods and collar type, and number of collared female elk used for analysis in
northwestern Wyoming during 1978–2012. Collar types were very high frequency (VHF) and global positioning system (GPS). NER refers to National Elk
Refuge. NPS refers to National Park Service. WGFD refers to Wyoming Game and Fish Department.
Capture years Project Method and collar type n
1978–1982 Smith and Robbins (1994) Trapping/darting; VHF 68
1994–1997 Smith et al. (2007) Darting; VHF 42
2005–2007 NER, unpublished Trapping/darting; VHF 31
2008–2011 NER, unpublished Darting; GPS 51
2007–2010 NPS, unpublished Darting; GPS 45
2008–2010 WGFD, unpublished Darting; GPS 4
2006–2010 Barbknecht et al. (2011) Net-gun; GPS 10
2010–2012 WGFD, unpublished Darting; GPS 29
880 The Journal of Wildlife Management 79(6)
features among hunt areas was not an issue because GPS fix-
rate success during open rifle season was 97%. Lastly, because
elk may have moved among hunt areas to avoid hunting
pressure, we examined differences in day-time and night-
time use of hunt areas; we found no statistical differences in
averaged individual elk-year proportional use of hunt areas.
Thus, all GPS data of elk during P3, regardless of capture
location, were combined for this analysis.
For both LDM and SDM, we computed proportion of
locations spent within 14 hunt areas during open rifle seasons
(18 Aug to 31 Jan) during P3 (Fig. 1). We then used a mixed
effects Cox proportional hazards model (Cox 1972,
Therneau et al. 2003) to evaluate relative harvest hazard
of each hunt area. This type of analysis uses locational data
(which hunt areas elk were within during open rifle season)
of all elk during a given date of harvest (month, day, and year)
to assess risk. We randomly selected 1 location per elk-day
only when individual elk visited multiple hunt areas during 1
day. We excluded non-harvest mortalities, which were
mostly of unknown causes, and used hunt area as a random
effect in R package coxme (Therneau et al. 2003).
We collected summer (Jul–Aug) calf/cow ratios from
multiple sources (Smith and Robbins 1994, Smith and
Anderson 1996, NPS and WGFD, unpublished data) which
were grouped by migratory status based on locations of aerial
surveys. We summed number of calves and cows observed
throughout the migratory range for each year surveyed and
plotted the calf/cow ratios for each period. We used analysis
of variance (ANOVA) to test for differences in mean calf/
cow ratios among periods for LDM. We also used a t-test
with the Welch degrees of freedom modification (Welch
1938) because of the assumption of unequal variances when
testing for statistical difference in calf/cow ratios between
LDM and SDM during P3. There were insufficient ratios for
SDM during P1 and P2 because the presence of a small
SDM population in the Wilson to Moose, Wyoming area
did not warrant summer surveys at that time.
RESULTS
During 1978–2012, 191 monitored females provided data
suitable for analysis. Multiple years of summer range
selection data were collected on 129 females, ranging from
2(n¼49) to 16 years (n¼1; Table S1, available online at
www.onlinelibrary.wiley.com). Only 3 individuals switched
between LDM and SDM. The model testing for a change in
the proportion of females being LDM fit the data well
(x2
189 ¼152.2, P¼0.98). There was a strong support for a
decrease in the probability of a marked female on the Refuge
being LDM during the years data were available (Table S1;
Fig. 2); the probability of a marked female being LDM
declined from 0.99 (95% CI ¼0.97–1.00) to 0.59 (95%
CI ¼0.47–0.70) between 1978 and 2012 (Fig. 2).
We amassed data on 553 elk-years and only 3 (0.5%) elk
switched summer ranges. Of these 3 elk, 2 switched from
LDM to SDM, an annual switching rate of 0.2%. Both elk
that switched from LDM to SDM came from Grand Teton
NP. The relationship between centroids in consecutive
summers was not correlated with distance to the Refuge
among the subset of 88 GPS-collared elk captured between
2006 and 2012 (Fig. S2, available online at www.
onlinelibrary.wiley.com).
We further assessed the plausibility of behavioral switching
as a primary driver of the observed change in LDM and
SDM behaviors using the observed switching rate in a simple
coupled geometric growth model assuming equal birth and
death rates between LDM and SDM. Given starting
populations of 8,000 and 100 in 1978, a net switching of
0.2% would result in a proportion LDM (SDM
t
/(SDM
t
þ
LDM
t
)) of 93% in 2012 which is higher than the observed
59% (Fig. S3, available online at www.onlinelibrary.wiley.
com).
Periods 1–3 contained 154, 143, and 244 LDM elk-years,
respectively. Only 2 SDM elk-years were observed during
P1; P2 and P3 contained 28 and 115 SDM elk-years,
respectively. Eighty-one percent (71/88) of mortalities were
due to harvest, including 2 wounding losses. Point estimates
of annual survival probability were lower, but not signifi-
cantly, during P1 (0.82, 0.75–0.89 95% CI) and P3 (0.83,
0.78–0.88 95% CI) than P2 (0.92, 0.88–0.97 95% CI) for
LDM elk (Fig. 3). Further, survival probabilities were not
significantly different between LDM and SDM elk during
any period.
During P3, we used 130,177 hunting-season GPS
locations to assess proportional use in hunt areas among
LDM and SDM elk. We used 231 elk-years and 30 harvest
mortalities in conjunction with 9,458 un-duplicated hunt-
ing-season elk GPS locations to assess hunt area-specific
hazard risks with hunt area 78 as the baseline. There was
variation in harvest availability; elk in hunt area 77 (the
Refuge) were the most available for harvest, whereas elk in
hunt area 78 were the least available (Fig. 4). The SDM spent
a high proportion of their time within the least hazardous
region, hunt area 78 (Fig. 5), but only 2% of hunting-season
locations were within the Bridger-Teton NF, a public
hunting tract within hunt area 78 (Fig. 1, Fig. S4, available
online at www.onlinelibrary.wiley.com). Compared to
SDM, LDM more often used multiple hunt areas (Fig. 5)
and were most likely to be found in hunt areas 75 and 77,
which were the most hazardous (Fig. 4).
Figure 2. Probability with 95% CI of a female elk marked during winter on
the National Elk Refuge, Wyoming, being from a long-distance migratory
(LDM) population segment, 1978–2012.
Cole et al. Elk Migratory Changes 881
There was an obvious decline in summer calf/cow ratios in
the LDM segments through time (Fig. 6); during P1 and P2,
LDM averaged 42 (SD ¼7) and 40 (SD ¼5) calves per 100
cows, respectively (F
2
¼24.1, P0.001). During P3, the
number of calves per 100 LDM cows decreased to 23
(SD ¼5), which was less than half of the 47 (SD ¼7) calves
per 100 cows in the SDM segment during the same time
period (T
6.09
¼6.25, P0.001).
DISCUSSION
We found an increase in the proportion of short-distance
migrants and a decrease in the proportion of long-distance
migrants captured from 1978 to 2012 on the Refuge,
suggesting commensurate changes in elk distribution in the
southern portion of the Greater Yellowstone Ecosystem
(GYE) and a decrease in the number of elk that undertake
long-distance migrations in the Jackson elk herd. We tested
4 hypotheses that could potentially influence the opposite
population growth trajectories between LDM and SDM of
the Jackson elk herd: behavioral switching rates, adult female
survival, harvest availability, and recruitment.
Annual survival rates of both LDM and SDM adult female
elk were 80–92%, which is similar to the average survival
rates of 85% from 26 studies (see Webb et al. 2011b). Most of
the change in survival rates appeared to be associated with the
time period rather than migration status because LDM and
SDM survival during a given time period were separated by
only a few percentage points. Smith’s (2007) finding that
Grand Teton NP elk had higher survival rates than elk from
elsewhere (i.e., Yellowstone NP, Gros Ventre, and Teton
Wilderness) during the 1990s may be attributed to including
both LDM and SDM elk from Grand Teton NP in his
analysis. Even though survival was comparable between both
elk segments during our study, harvest availability varied.
Figure 4. Relative hazard of hunt areas derived from a combination of
global positioning system (GPS) data during open hunting seasons and
harvested female elk during 2006–2012 in northwestern Wyoming.
Coefficient estimates are relative to hunt area 78 and the horizontal dotted
line indicates 1 where there is no difference. Error bars are standard error.
Histogram bars are not visible for several hunt areas because of very low
relative hazard values.
Figure 5. Average proportional use of hunt areas by long-distance
migratory (gray) and short-distance migratory (white) individual female
elk in northwestern Wyoming during 2006–2012. Classification of long and
short distance migratory elk were based from centroids of summer (Jul–Sep)
home ranges. Error bars denote standard deviations.
Figure 6. Box plots of summer calf/cow ratios from long-distance migratory
(LDM) and short-distance migratory (SDM) elk during 3 periods in
northwestern Wyoming. Periods (P) 1, 2, and 3 were during 1978–1984,
1994–2000, and 2006–2012, respectively. The dark line inside of boxes
indicates the median and the top and bottom of the boxes are 25th and 75th
percentiles, respectively (the entire box contains 50% of the data). Outliers,
defined as being outside of the inter-quartile range times 1.5, are represented
by dots outside of the box.
Figure 3. Annual survival rates of long-distance migratory (LDM) and
short-distance migratory (SDM) female elk during 3 temporal periods in
northwestern Wyoming. Only 2 SDM elk-years were available during
period 1 (P1). Period 1 ¼1978–1984, P2 ¼1994–2000, and P3 ¼2006–
2012. Error bars show 95% confidence intervals.
882 The Journal of Wildlife Management 79(6)
The SDM spent a high proportion of time within hunt area
78, an area with a large amount of privately owned lands with
limited hunter access. However, when SDM elk left summer
ranges to enter the Refuge (hunt area 77), vulnerability
increased and survival rates likely decreased. In recent years,
wildlife managers have structured hunts to limit harvest of
the northern migrants (e.g., Yellowstone NP and Teton
Wilderness elk) and secure public access to private lands to
improve harvest rates and decrease numbers of SDM elk that
occupy the Wilson to Moose, Wyoming area. Although
there is opportunity to direct harvest activities toward hunt
areas based on the proportional use of various hunt areas by
elk, the highly consistent survival rates among both
subpopulations indicate this management strategy may not
be sufficient to reverse trends in the proportional change
between SDM and LDM.
Hunting mortality of calves may affect recruitment rates
because calves are an important element of elk population
dynamics (Raithel et al. 2007). Work done by Smith and
Anderson (1998) indicated hunting mortality did not differ
between calves and adult elk; however, this was during the
early 1990s when number of hunters was 3 times greater
associated with the relatively large Jackson elk herd
population size (D. Brimeyer, WGFD, personal communi-
cation). During the early 1990s, hunting seasons promoted
harvest of LDM elk through hunting seasons that extended
into November for general and limited quota licenses.
Between 1993 and 1997, an average of 1,920 limited quota
any elk licenses were offered each year in the northern hunt
areas of the Jackson elk herd unit, in which LDM elk
migrate. Hunter numbers in the Jackson herd averaged over
9,190 hunters during this time period. In recent years,
hunting seasons have been designed to protect LDM elk
while increasing harvest of SDM elk. Since 2012, no limited
quota any elk licenses have been offered in the hunt areas that
focused hunting pressure on LDM. Hunter numbers since
2012 (2012–2014) averaged 2,985 hunters. Although
hunting seasons and quotas have become more conservative
for the areas where LDM are more vulnerable, the hunt units
for the SDM have been liberalized through the addition of
license types and extending season lengths to the end of
January (Hunt Area 78).
We also explored whether elk switched from LDM to
SDM summer ranges and whether the switching rates were
high enough to alter population growth trajectories during
the 35-year study period. Switching from LDM to SDM was
extremely low (0.002 elk-years), which supports the general
consensus that female elk exhibit high site fidelity (Irwin and
Peek 1983, Edge et al. 1986, Webb et al. 2011a). Further, elk
herds elsewhere with resident and migratory segments also
exhibited low switching rates (Hebblewhite and Merrill
2007, Middleton et al. 2013a). However, juvenile elk in the
Jackson elk herd had high dispersal rates in the early 1990s,
which may be attributed to density effects when the
population peaked at approximately 18,000 elk (Smith
and Anderson 2001). Additionally, the authors did not test
whether dispersing elk were relocating to the Wilson to
Moose, Wyoming area or to other summer ranges within our
study area. Our model also indicated that the switching rate
from LDM to SDM was not sufficient to account for the
observed declines in the proportion of LDM. Similarly,
Smith and Anderson (2001) determined that switching
(dispersing) did not differentially influence population
growth of summer herd segments within the Jackson elk
herd.
Recruitment, a key driver in elk population dynamics
(Gaillard et al. 1998, Raithel et al. 2007), appears to be the
primary driver of the decline in LDM. Recruitment, as
indexed by summer calf/cow ratios, in LDM declined and
during recent years was half of summer calf/cow ratios
observed in SDM elk (Fig. 6). The current 23 calves per 100
cows in LDM is considered low recruitment (White et al.
2010) and is nearly half of historical LDM summer calf/cow
ratios (Fig. 6). Potential effects on summer calf/cow ratios
include pregnancy rates influenced by winter range con-
ditions (Thorne et al. 1976, Weber et al. 1984), spring
weather conditions (Lubow and Smith 2004, Smith et al.
2006), forage quality and quantity through summer climate
(Cook et al. 2004), elk density (Stewart et al. 2005), sex and
age composition (Albon et al. 1986, Noyes et al. 1996), and
predators, both directly and indirectly (Barber-Meyer et al.
2008, Creel and Christianson 2008).
We did not have sufficient data to model influences on
summer calf/cow ratios although we conducted exploratory
analyses to examine changes in environmental covariates
throughout the study period (Supplementary Material 1,
available online at www.onlinelibrary.wiley.com). There is
likely a differential exposure to predation between SDM and
LDM elk because SDM are likely partially buffered from
predators (Hebblewhite and Merrill 2007). Neonate preda-
tion by grizzly bears (Ursus arctos) has increased since the
1980s (Middleton et al. 2013b) and winter calf/cow ratios
were significantly negatively correlated with grizzly bear
density at a herd-unit scale in the southern portion of the
GYE (Foley et al. 2015). Wolves also prey on neonates but
probably to a lesser extent than grizzly bears (Barber-Meyer
et al. 2008, Griffin et al. 2011). Wolves can affect
recruitment in 2 ways—directly and indirectly. Wolves
directly predate calves but also may increase anti-predator
behavior in cow elk (see Garrott et al. 2005) that results in
reduced pregnancy rates (Creel and Winnie 2005, Christian-
son and Creel 2010). In 2006–2007, only 70% (53/76) of
adult female elk sampled during January–March in Buffalo
Valley, within the LDM summer range of the Jackson herd
unit, were pregnant (S. Fairbanks, Iowa State University,
unpublished data), and 71% of migratory elk in Clark’s Fork
herd unit were pregnant when sampled during winters of
2008–2010 (Middleton et al. 2013a). These pregnancy rates
were considerably lower than the 89% (141/158) rate from 3
feedgrounds (Bench Corral, Soda Lake, and Scab Creek) in
the Pinedale, Piney, and Upper Green River herd units
during 2006–2007 (Barbknecht et al. 2011, S. Fairbanks,
unpublished data) personal communication; Fig. S6,
available online at www.onlinelibrary.wiley.com). During
the years when pregnancy data were collected, Jackson and
Clark’s Fork had 79% higher indices of wolf densities than
Cole et al. Elk Migratory Changes 883
the 3 feedgrounds (Foley et al. 2015). Further, during 1976–
1982 when wolves were not present on our study area, the
Refuge had an 87% pregnancy rate (Smith and Robbins
1994) that did not differ from the 86% rate in 1998–2002
when wolves were colonizing Jackson Hole (Smith et al.
2006). The inverse relationship between pregnancy rates and
wolf density might suggest that anti-predator behavior
affects pregnancy rates. Comparing pregnancy rates between
elk with and without supplemental feed via winter feed-
grounds may not be appropriate, but the phenomenon of
lower pregnancy rates in relation to higher predation risk has
been observed throughout the GYE (Creel et al. 2011).
However, lower recruitment rates may also be manifested
through weather conditions (Proffitt et al. 2014) and forage
quantity and quality (Cook et al. 2001, 2004) via changes in
climate patterns (Middleton et al. 2013a) and weather-
mediated predisposition of neonates to predation and disease
(Smith et al. 2006). Foley et al. (2015) found a positive
correlation in winter calf/cow ratios with previous year
summer rainfall and a negative correlation with previous year
maximum snow-water equivalent. Climate and predation
data at a finer spatial and temporal scale are required to better
understand their relative impacts on elk recruitment.
MANAGEMENT IMPLICATIONS
The proportional decline of LDM compared to SDM has
significant management implications for the Jackson elk
herd. This change suggests that long-distance migratory
elk have declined over a 35-year time period, and short
distance migrants that summer immediately adjacent to the
Refuge winter range have increased dramatically. Long-
distance migratory elk populations are biologically and
economically important, and strategies designed to protect
long-distance migratory elk may limit the ability of elk
managers to reduce the Refuge population to objective
levels. Population objectives are 11,000 elk for the Jackson
elk herd, with 5,000 of these wintering on the Refuge
(USFWS and NPS 2007), but 2014 surveys enumerated
approximately 11,600 elk in the Jackson elk herd with
8,300 of these wintering on the Refuge (WGFD 2014).
Current harvest strategies such as modified hunt area
boundaries and hunting season dates designed to protect
LDM may have little effect because survival rates of adult
female elk, which are mostly determined by harvest, were
comparable between LDM and SDM population segments
based on our data. Low recruitment rates appear to be
driving the decline of the LDM segment, which limits
remedial options of wildlife managers. Conversely, strate-
gies to maximize harvest of SDM have proved insufficient
to offset high recruitment among SDM and meet the
Refuge population objectives. Failure to reduce elk
numbers to the Refuge population objective will necessitate
continued reliance on supplemental feeding, higher
prevalence, and risk of density-dependent disease outbreaks
throughout the Jackson elk herd, and continued loss of
shrub and woodland communities on the Refuge due to
browsing by large numbers of elk (Smith et al. 2004,
USFWS and NPS 2007).
ACKNOWLEDGMENTS
We thank D. Thoma and P. Farnes for sharing climatic data.
W. Ketchum and D. Harris assisted with compilation of
historical elk data. Graduate students A. Barbknecht and F.
Henry worked on ISU’s elk study, which was funded by
WGFD, Morris Animal Foundation, ISU, and Wyoming
Wildlife-Livestock Disease Partnership. T. Pratt and T.
Schoultz assisted with data collection for the Refuge.
Funding for A. M. Foley and P. C. Cross was provided by
National Science Foundation and National Institutes of
Health Ecology of Infectious Disease (grant number DEB-
1067129) and the United States Geological Survey. The
findings and conclusions in this article are those of the
authors and do not necessarily represent the views of the U.S.
Fish and Wildlife Service and Wyoming Game and Fish
Department. Any mention of trade, product, or firm names is
for descriptive purposes only and does not imply endorse-
ment by the U.S. Government.
LITERATURE CITED
Albon, S., B. Mitchell, B. Huby, and D. Brown. 1986. Fertility in female red
deer (Cervus elaphus): the effects of body composition, age and
reproductive status. Journal of Zoology 209:447–460.
Allendorf, F. W., P. R. England, G. Luikart, P. A. Ritchie, and N. Ryman.
2008. Genetic effects of harvest on wild animal populations. Trends in
Ecology & Evolution 23:327–337.
Anderson, C. C. 1958. The elk of Jackson Hole: a review of Jackson elk
studies. Bulletin 10, Wyoming Game and Fish Commission, Cheyenne,
Wyoming, USA.
Anderson, E. M. 2007. Changes in bird communities and willow habitats
associated with fed elk. Wilson Journal of Ornithology 119:400–409.
Barber-Meyer, S. M., L. D. Mech, and P. J. White. 2008. Elk calf survival
and mortality following wolf restoration to Yellowstone National Park.
Wildlife Monographs 169:1–30.
Barbknecht, A. E., W. S. Fairbanks, J. D. Rogerson, E. J. Maichak, B. M.
Scurlock, and L. L. Meadows. 2011. Elk parturition site selection at local
and landscape scales. Journal of Wildlife Management 75:646–654.
Berger, J. 2004. The last mile: how to sustain long-distance migration in
mammals. Conservation Biology 18:320–331.
Bergerud, A., R. Ferguson, and H. Butler. 1990. Spring migration and
dispersion of woodland caribou at calving. Animal Behaviour 39:360–368.
Boyce, M. S. 1989. Elk management in North America: the Jackson herd.
Cambridge Press, Cambridge, United Kingdom.
Caccamise, D. F., L. M. Reed, P. M. Castelli, S. Wainright, and T. C.
Nichols. 2000. Distinguishing migratory and resident Canada geese
using stable isotope analysis. Journal of Wildlife Management 64:1084–
1091.
Christianson, D., and S. Creel. 2010. A nutritionally mediated risk effect of
wolves on elk. Ecology 91:1184–1191.
Cole, G. F. 1969. The elk of Grand Teton and southern Yellowstone
National Parks. Research Report GRTE-N-1, and manuscript for Fauna
of the National Parks of the United States. U.S. National Park Service,
Office of Natural Science Studies, Washington, D.C., USA.
Cook, R. C., J. G. Cook, and L. D. Mech. 2004. Nutritional condition of
northern Yellowstone elk. Journal of Mammalogy 85:714–722.
Cook, R. C., D. L. Murray, J. G. Cook, P. Zager, and S. L. Monfort. 2001.
Nutritional influences on breeding dynamics in elk. Canadian Journal of
Zoology 79:845–853.
Cox, D. R. 1972. Regression models and life tables. Journal of Royal
Statistical Society, Series B 34:187–220.
Craighead, J. J., G. Atwell, and B. W. O’Gara. 1972. Elk migrations in and
near Yellowstone National Park. Wildlife Monographs 29:3–48.
Creel, S., and D. Christianson. 2008. Relationships between direct
predation and risk effects. Trends in Ecology & Evolution 23:194–201.
Creel, S., D. A. Christianson, and J. A. Winnie Jr. 2011. A survey of the
effects of wolf predation risk on pregnancy rates and calf recruitment in
elk. Ecological Applications 21:2847–2853.
884 The Journal of Wildlife Management 79(6)
Creel, S., J. Winnie Jr, B. Maxwell, K. Hamlin, and M. Creel. 2005. Elk
alter habitat selection as an antipredator response to wolves. Ecology
86:3387–3397.
Edge, W. D., C. L. Marcum, S. L. Olson, and J. F. Lehmkuhl. 1986.
Nonmigratory cow elk herd ranges as management units. Journal of
Wildlife Management 50:660–663.
Foley,A.M.,P.C.Cross,D.A.Christianson,B.M. Scurlock,and S.Creel.2015.
Influences of supplemental feeding on winter elk calf:cow ratios in the
southern greater Yellowstone ecosystem. Journal of Wildlife Management
79:in press.
Frair, J. L., S. E. Nielsen, E. H. Merrill, S. R. Lele, M. S. Boyce, R. H.
M. Munro, G. B. Stenhouse, and H. L. Beyer. 2004. Removing GPS
collar bias in habitat selection studies. Journal of Applied Ecology
41:201–212.
Franson, J. C., and B. L. Smith. 1988. Septicemic pasteurellosis in elk
(Cervus elaphus) on the United States National Elk Refuge, Wyoming.
Journal of Wildlife Diseases 24:715–717.
Fryxell, J., and A. Sinclair. 1988. Causes and consequences of migration by
large herbivores. Trends in Ecology & Evolution 3:237–241.
Gaillard, J.-M., M. Festa-Bianchet, and N. G. Yoccoz. 1998. Population
dynamics of large herbivores: variable recruitment with constant adult
survival. Trends in Ecology & Evolution 13:58–63.
Garrott, R. A., J. A. Gude, E. J. Bergman, C. Gower, P. White, and K. L.
Hamlin. 2005. Generalizing wolf effects across the Greater Yellowstone
Area: a cautionary note. Wildlife Society Bulletin 33:1245–1255.
Gasson, W. 1987. Managing elk the Wyoming way. Wyoming Wildlife
9:16–25.
Griffin, K. A., M. Hebblewhite, H. S. Robinson, P. Zager, S. M. Barber-
Meyer, D. Christianson, S. Creel, N. C. Harris, M. A. Hurley, D. H.
Jackson, B. K. Johnson, W. L. Myers, J. D. Raithel, M. Schlegel, B. L.
Smith, C. White, and P. J. White. 2011. Neonatal mortality of elk driven
by climate, predator phenology and predator community composition.
Journal of Animal Ecology 80:1246–1257.
Haggerty, J. H., and W. R. Travis. 2006. Out of administrative control:
absentee owners, resident elk and the shifting nature of wildlife
management in southwestern Montana. Geoforum 37:816–830.
Hebblewhite, M., and E. H. Merrill. 2007. Multiscale wolf predation risk
for elk: does migration reduce risk? Oecologia 152:377–387.
Hebblewhite, M., and E. H. Merrill. 2011. Demographic balancing of
migrant and resident elk in a partially migratory population through
forage-predation tradeoffs. Oikos 120:1860–1870.
Heisey, D. M., and B. R. Patterson. 2006. A review of methods to estimate
cause-specific mortality in presence of competing risks. Journal of Wildlife
Management 70:1544–1555.
Herriges, J. D., T. E. Thorne, and S. L. Anderson. 1992. Vaccination to
control brucellosis in free-ranging elk on western Wyoming feed grounds.
Pages 107–112 in R. D. Brown, editor. The biology of deer. Springer-
Verlag, New York, New York, USA.
Irwin, L. L., and J. M. Peek. 1983. Elk habitat use relative to forest
succession in Idaho. Journal of Wildlife Management 47:664–672.
Levin, P. S., E. E. Holmes, K. R. Piner, and C. J. Harvey. 2006. Shifts in a
Pacific Ocean fish assemblage: the potential influence of exploitation.
Conservation Biology 20:1181–1190.
Lubow, B. C., and B. L. Smith. 2004. Population dynamics of the Jackson
elk herd. Journal of Wildlife Management 68:810–829.
Martinka, C. 1969. Population ecology of summer resident elk in Jackson
Hole, Wyoming. Journal of Wildlife Management 33:465–481.
Mauritzen, M., A. E. Derocher, Ø. Wiig, S. E. Belikov, A. N. Boltunov, E.
Hansen, and G. W. Garner. 2002. Using satellite telemetry to define
spatial population structure in polar bears in the Norwegian and western
Russian Arctic. Journal of Applied Ecology 39:79–90.
Mbaiwa, J. E., and O. I. Mbaiwa. 2006. The effects of veterinary fences on
wildlife populations in Okavango Delta, Botswana. International Journal
of Wilderness 12:17–23.
McCullough, D. R. 1985. Long range movements of large terrestrial
mammals. Pages 444–465 in M. A. Rankin, editor. Contributions in
marine science. University of Texas Marine Science Institute, Port
Aransas, Texas, USA.
Middleton, A. D., M. J. Kauffman, D. E. McWhirter, J. G. Cook, R. C.
Cook, A. A. Nelson, M. D. Jimenez, and R. W. Klaver. 2013a. Animal
migration amid shifting patterns of phenology and predation: lessons from
a Yellowstone elk herd. Ecology 94:1245–1256.
Middleton, A. D., T. A. Morrison, J. K. Fortin, C. T. Robbins, K. M.
Proffitt, P. White, D. E. McWhirter, T. M. Koel, D. G. Brimeyer, and W.
S. Fairbanks. 2013b. Grizzly bear predation links the loss of native trout to
the demography of migratory elk in Yellowstone. Proceedings of the Royal
Society B: Biological Sciences 280:20130870.
Milner-Gulland, E., J. M. Fryxell, and A. R. E. Sinclair. 2011. Animal
migration: a synthesis. Oxford University Press, Oxford, United Kingdom.
Murie, O. J. 1951. The elk of North America. Stackpole Books, Harrisburg,
Pennsylvania, USA.
Neter, J., M. H. Kutner, C. J. Nachtsheim, and W. Wasserman. 1996.
Applied linear statistical models. Fourth edition. McGraw-Hill, New
York, New York, USA.
Nielson, R. M., B. F. Manly, L. L. McDonald, H. Sawyer, and T. L.
McDonald. 2009. Estimating habitat selection when GPS fix success is
less than 100%. Ecology 90:2956–2962.
Noyes, J. H., B. K. Johnson, L. D. Bryant, S. L. Findholt, and J. W. Thomas.
1996. Effects of bull age on conception dates and pregnancy rates of cow
elk. Journal of Wildlife Management 60:508–517.
Oehlert, G.W. 1992. A note on the Delta method. American Statistician
46:27–29.
Proffitt, K., J. Cunningham, K. L. Hamlin, and R. A. Garrott. 2014.
Bottom-up and top-down influences on pregnancy rates and recruitment
of Northern Yellowstone Elk. Journal of Wildlife Management 78:1383–
1393.
R Development Core Team. 2005. R: a language and environment for
statistical computing. R Foundation for Statistical Computing, Vienna,
Austria.
Raithel, J. D., M. J. Kauffman, and D. H. Pletscher. 2007. Impact of spatial
and temporal variation in calf survival on the growth of elk populations.
Journal of Wildlife Management 71:795–803.
Reiss, H., G. Hoarau, M. Dickey-Collas, and W. J. Wolff. 2009. Genetic
population structure of marine fish: mismatch between biological and
fisheries management units. Fish and Fisheries 10:361–395.
Robinson, B. G., M. Hebblewhite, and E. H. Merrill. 2010. Are migrant
and resident elk (Cervus elaphus) exposed to similar forage and predation
risk on their sympatric winter range? Oecologia 164:265–275.
Rudd, W. J., A. L. Ward, and L. L. Irwin. 1983. Do split hunting seasons
influence elk migrations from Yellowstone National Park? Wildlife
Society Bulletin 11:328–331.
Samuel, W., D. Welch, and B. Smith. 1991. Ectoparasites from elk (Cervus
elaphus nelsoni) from Wyoming. Journal of Wildlife Diseases 27:446–451.
Sargeant, G. A. 2011. wild1: R tools for wildlife research and management.
R package version 1. <http://cran.r-project.org/web/packages/wild1/
vignettes/csm.pdf>. Accessed 18 Apr 2013.
Smith, B. L. 2007. Migratory behavior of hunted elk. Northwest Science
81:251–264.
Smith, B. L. 2011. Where elk roam: conservation and biopolitics of our
national elk herd. Lyons Press, Guilford, Connecticut, USA.
Smith, B. L., and S. H. Anderson. 1996. Patterns of neonatal mortality of elk
in northwest Wyoming. Canadian Journal of Zoology 74:1229–1237.
Smith, B. L., and S. H. Anderson. 1998. Juvenile survival and population
regulation of the Jackson elk herd. Journal of Wildlife Management
62:1036–1045.
Smith, B. L., and S. H. Anderson. 2001. Does dispersal help regulate the
Jackson elk herd? Wildlife Society Bulletin 29:331–341.
Smith, B. L., E. K. Cole, and D. S. Dobkin. 2004. Imperfect pasture: a
century of change at the National Elk Refuge in Jackson Hole, Wyoming.
Grand Teton Natural History Association, Moose, Wyoming, USA.
Smith, B. L., and R. L. Robbins. 1994. Migrations and management of the
Jackson elk herd. National Biological Survey Resource Publication 199,
Washington, D.C., USA.
Smith, B., and T. Roffe. 1997. Evaluation of studies of Strain 19 Brucella
abortus vaccine in elk: clinical trials and field applications. National Elk
Refuge and U.S. Fish and Wildlife Service Final Report, Jackson,
Wyoming, USA.
Smith, B. L., E. S. Williams, K. C. McFarland, T. L. McDonald, G. Wang,
and T. D. Moore. 2006. Neonatal mortality of elk in Wyoming:
Environmental, population, and predator effects, Biological Technical
Publication BTP-R6007-2006, Washington, D.C., USA.
Solberg, E. J., B. E. Saether, O. Strand, and A. Loison. 1999. Dynamics of a
harvested moose population in a variable environment. Journal of Animal
Ecology 68:186–204.
Cole et al. Elk Migratory Changes 885
Stewart, K. M., R. T. Bowyer, B. L. Dick, B. K. Johnson, and J. G. Kie.
2005. Density-dependent effects on physical condition and reproduction
in North American elk: an experimental test. Oecologia 143:85–93.
Tacha, T. C., P. A. Vohs, and G. C. Iverson. 1984. Migration routes of
sandhill cranes from mid-continental North America. Journal of Wildlife
Management 48:1028–1033.
Therneau, T. M., P. M. Grambsch, and V. S. Pankratz. 2003. Penalized
survival models and frailty. Journal of computational and graphical
statistics 12:156–175.
Thorne, E. T., R. E. Dean, and W. G. Hepworth. 1976. Nutrition during
gestation in relation to successful reproduction in elk. Journal of Wildlife
Management 40:330–335.
U.S. Fish and Wildlife Service [USFWS] and National Park Service [NPS].
2007. Bison and Elk Management Plan: National Elk Refuge, Grand
Teton National Park. USFWS and NPS, Lakewood, Colorado, USA.
Webb, S., M. Dzialak, S. Harju, L. Hayden-Wing, and J. Winstead. 2011a.
Influence of land development on home range use dynamics of female elk.
Wildlife Research 38:163–167.
Webb, S. L., M. R. Dzialak, J. J. Wondzell, S. M. Harju, L. D. Hayden-
Wing, and J. B. Winstead. 2011b. Survival and cause-specific mortality of
female Rocky Mountain elk exposed to human activity. Population
Ecology 53:483–493.
Weber, B. J., M. L. Wolfe, G. C. White, and M. M. Rowland. 1984.
Physiologic response of elk to differences in winter range quality. Journal
of Wildlife Management 48:248–253.
Welch, B. L. 1938. The significance of the difference between two
means when the population variances are unequal. Biometrika 29:30–
362.
White, C. G., P. Zager, and M. W. Gratson. 2010. Influence of predator
harvest, biological factors, and landscape on elk calf survival in Idaho.
Journal of Wildlife Management 74:355–369.
Wilcove, D. S., and M. Wikelski. 2008. Going, going, gone: is animal
migration disappearing. PLoS biology 6:e188.
Wilson, R. M. 2002. Directing the flow: migratory waterfowl, scale,
and mobility in western North America. Environmental History 7:247–
266.
Woods, J. G. 1991. Ecology of a partially migratory elk population.
Dissertation, University of British Columbia, Vancouver, Canada.
Worton, B. 1987. A review of models of home range for animal movement.
Ecological Modelling 38:277–298.
Wyoming Game and Fish Department [WGFD]. 2014. Annual big game
herd unit job completion reports. WGFD, Cheyenne, Wyoming, USA.
Associate Editor: Scott McCorquodale.
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