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Survival of Translocated Bighorn Sheep In the Deadwood Region of the Black Hills, South Dakota

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ABSTRACT—Bighorn Sheep (Ovis canadensis) historically inhabited the Black Hills region of South Dakota, but the species was extirpated from the area in the early 1900s concurrent with declines in population throughout their entire North American range. Translocation is a common management tool allowing for accelerated colonization of historic Bighorn Sheep habitat, but many attempts are unsuccessful. Mountain Lions (Puma concolor) and pneumonia are generally considered the most common limiting factors to Bighorn Sheep populations. Twenty-six Bighorn Sheep were translocated from Alberta, Canada to the Deadwood region of the northern Black Hills, an area with both a resident Mountain Lion population and potential for contact with Domestic Sheep (Ovis aries) and Goats (Capra hircus), known carriers of pathogens that are lethal to Bighorn Sheep. Adult survival and natality increased the population substantially in year 1, however, the only breedingage male was euthanized owing to concerns about potential for pathogen transmission from Domestic Sheep and Goats. In year 2, the population experienced a pneumonia outbreak, resulting in 57.9% of all mortalities during the study period. Mountain Lion predation was not detected, nor was direct contact with Domestic Sheep or Goats observed. Intensive monitoring was critical in determining the outcome of the translocation.
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Survival of Translocated Bighorn Sheep In the Deadwood
Region of the Black Hills, South Dakota
Author(s): Ty J Werdel, Jonathan A Jenks, Thomas E Besser, John T Kanta,
Chadwick P Lehman, Teresa J Frink
Source: Northwestern Naturalist, 99(3):222-231.
Published By: Society for Northwestern Vertebrate Biology
https://doi.org/10.1898/NWN18-06.1
URL: http://www.bioone.org/doi/full/10.1898/NWN18-06.1
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SURVIVAL OF TRANSLOCATED BIGHORN SHEEP IN THE
DEADWOOD REGION OF THE BLACK HILLS, SOUTH DAKOTA
TYJWERDEL
1
,JONATHAN AJENKS
Department of Natural Resource Management, South Dakota State University, Edgar S. McFadden Biostress
Lab, Brookings, SD 57007 USA
THOMAS EBESSER
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164
USA
JOHN TKANTA
South Dakota Game, Fish and Parks, 4130 Adventure Trail, Rapid City, SD 57702 USA
CHADWICK PLEHMAN
South Dakota Game, Fish and Parks, 13329 US Highway 16A, Custer, SD 57730 USA
TERESA JFRINK
Department of Applied Sciences, Chadron State College, Burkhiser Complex, Chadron, NE 69337 USA
ABSTRACT—Bighorn Sheep (Ovis canadensis) historically inhabited the Black Hills region of South
Dakota, but the species was extirpated from the area in the early 1900s concurrent with declines in
population throughout their entire North American range. Translocation is a common management
tool allowing for accelerated colonization of historic Bighorn Sheep habitat, but many attempts are
unsuccessful. Mountain Lions (Puma concolor) and pneumonia are generally considered the most
common limiting factors to Bighorn Sheep populations. Twenty-six Bighorn Sheep were
translocated from Alberta, Canada to the Deadwood region of the northern Black Hills, an area
with both a resident Mountain Lion population and potential for contact with Domestic Sheep (Ovis
aries) and Goats (Capra hircus), known carriers of pathogens that are lethal to Bighorn Sheep. Adult
survival and natality increased the population substantially in year 1, however, the only breeding-
age male was euthanized owing to concerns about potential for pathogen transmission from
Domestic Sheep and Goats. In year 2, the population experienced a pneumonia outbreak, resulting
in 57.9% of all mortalities during the study period. Mountain Lion predation was not detected, nor
was direct contact with Domestic Sheep or Goats observed. Intensive monitoring was critical in
determining the outcome of the translocation.
Key words: Bighorn Sheep, Black Hills, mortality, Mycoplasma ovipneumoniae,Ovis canadensis,
pneumonia, population, South Dakota, survival, translocation
Prior to the arrival of European Americans to
western North America, Bighorn Sheep (Ovis
canadensis) were abundant in most mountain
ranges and ‘‘badlands’’ along major rivers and
principal tributaries from their easternmost
range in the Pine Ridge region of South Dakota
to the westernmost regions of North America
(Buechner 1960). Although it may be impossible
to accurately determine population numbers of
Bighorn Sheep prior to the expansion of western
settlement, Seton’s (1929) population estimate of
1.5–2 million individuals provides a credible
baseline to compare to contemporary status
(Buechner 1960). Bighorn Sheep are an ecologi-
cally sensitive species, with many factors affect-
1
Current Address: Department of Horticulture and
Natural Resources, Kansas State University, Man-
hattan, KS 66506 USA; werdel@ksu.edu
222
NORTHWESTERN NATURALIST 99:222–231 WINTER 2018
ing their wilderness habitat (Buechner 1960).
Human impacts in the form of uncontrolled
harvest, introduced disease from Domestic
Sheep (Ovis aries), introduced forage competition
from domestic livestock, reduced and fragment-
ed habitat, and loss of movement corridors led
to major declines in Bighorn Sheep populations
in the late 19th century through the mid-20th
century (Buechner 1960). Since the mid-1900s,
state and federal wildlife management agencies
have attempted over 1,000 Bighorn Sheep
reintroductions to the species’ historic ranges,
with varying levels of success (Berger 1990;
Singer and others 2000a; Hedrick 2014; Parr
2015; WAFWA 2015).
In South Dakota, Bighorn Sheep historically
inhabited the Black Hills region, but the species
was extirpated from the area in the early 1900s
(Seton 1929; Witte and Gallagher 2012). South
Dakota Department of Game, Fish and Parks
(SDGFP) began reintroductions to the state in the
1960s, with successful restorations occurring in
Badlands National Park and the central and
southern regions of the Black Hills, including the
Custer State Park, Spring Creek, Rapid Creek,
Sheridan Lake, and Elk Mountain areas (Zim-
merman 2008; SDGFP 2013; Parr 2015). Howev-
er, the Deadwood area of the northern Black
Hills remained vacant, but deemed potentially
suitable for a reintroduction, based on habitat
suitability models and a qualitative assessment
of topography, forage, and water (SDGFP 2013).
Despite a prerelease habitat evaluation, no
information was available regarding historical
use of the immediate release site in the Dead-
wood region by Bighorn Sheep (SDGFP 2013).
Diseases and parasites can cause significant
mortality in Bighorn Sheep. The pneumonia
complex includes a number of causative agents
including lungworms (Protostrongylus spp.) and
bacteria (Mannheimia haemolytica,Bibersteinia
trehalosi,Mycoplasma ovipneumoniae; Besser and
others 2013) that become mortality agents
affecting Bighorn Sheep when present in con-
junction with other stressors, such as nutrition
and climate (Onderka and Wishart 1984; Foreyt
1990; Besser and others 2012). However, evi-
dence shows that Mycoplasma ovipneumoniae is
the most supported and parsimonious explana-
tion as the initiating agent for epidemic pneu-
monia (Besser and others 2013). Domestic Sheep
and Bighorn Sheep carrying these pathogenic
agents can transmit them to na¨
ıve Bighorn Sheep
populations if contact occurs (Besser and others
2014). Plowright and others (2013) documented
that surviving ewes become immune to the
effects of these pathogens, but that immunity is
not transferred to lambs. Cassirer and Sinclair
(2007) noted that pneumonia caused 43% of
mortalities of adult Bighorn Sheep occupying
Hells Canyon, Idaho, Oregon, and Washington.
They designated pneumonia-caused mortality as
the primary factor limiting population growth of
Bighorn Sheep. In that study, Mountain Lion
(Puma concolor) predation accounted for 27% of
Bighorn Sheep mortalities, but was not associat-
ed with population decline. In contrast, McKin-
ney and others (2006) observed no significant
diseases in Bighorn Sheep in the Mazatzal
Mountains, Arizona. However, they hypothe-
sized that Mountain Lion predation and nutri-
tional condition influenced population status of
Bighorn Sheep and suggested that short-term
removal of Mountain Lions contributed to
increased productivity and consequently, popu-
lation growth. In the Black Hills, lamb survival
of Bighorn Sheep occupying Spring Creek,
Rapid Creek, and Hill City was 2% over a 3-y
period (2010–2012) due to disease and predation
(Smith and others 2014). In contrast, Parr and
others (2018) found that in the absence of
disease, lamb survival in the Black Hills can
reach as high as 44%.
It has been suggested that Mountain Lions
pose a significant threat to Bighorn Sheep
populations due to ease of capture of this prey
species (Rominger and others 2004; Festa-Bian-
chet and others 2006). Predation by Mountain
Lions was the primary proximate cause of
mortality (75% of mortalities) on Bighorn Sheep
in one population in Arizona (Rominger and
others 2004). Moreover, Kamler and others
(2002) documented that Mountain Lions caused
66% of mortality on a translocated Bighorn
Sheep population in Arizona. In California,
Mountain Lions were responsible for 69% of
Bighorn Sheep mortalities (Hayes and others
2000). In contrast, others have suggested that
Mountain Lions cause limited mortality to Big-
horn Sheep and other large mammal popula-
tions (Rominger and others 2004; Cougar
Management Guidelines Working Group 2005).
In the Black Hills, lamb production and survival
are generally correlated with time since birth,
and populations of Bighorn Sheep can experi-
ence disease-mediated lamb mortality later in
WINTER 2018 223
WERDEL AND OTHERS:DEADWOOD BIGHORN SHEEP
the season than mortality due to Mountain Lions
(Smith and others 2014). However, other pred-
ators such as Coyotes (Canis latrans; Dekker
2009) and Bobcats (Lynx rufus; Parr and others
2014) have been associated with Bighorn Sheep
mortality.
To expand Bighorn Sheep restoration in the
Black Hills, 26 Bighorn Sheep were translocated
from the Luscar Mine near Hinton, Alberta,
Canada to the Deadwood region of the northern
Black Hills. In an effort to evaluate a critical large
mammal translocation, our objectives were to:
determine annual survival rates of Bighorn
Sheep, determine cause-specific mortality of
Bighorn Sheep, and to estimate growth rate of
the Deadwood herd.
METHODS
Study Area
Bighorn Sheep were initially captured in
Alberta, Canada, and translocated to our study
area, the Deadwood region, located in the
northern Black Hills in western South Dakota,
USA (UTM: Zone 13, 602979 E, 4911453 N) (Fig.
1). This area encompasses approximately 8177
ha of public (5203 ha) and private (2974 ha) land
and is located immediately adjacent to the
Deadwood, Lead, and Central City communities
in Lawrence County, South Dakota (SDGFP
2013). Elevations range from 1073 to 2209 m
above mean sea level. The Deadwood region of
the Black Hills lies in the central core of the
Blacks Hills, which is typified by canyons,
mountain peaks, and broad valleys (Hoffman
and Alexander 1987). Soils of the region include
limestones, dolomites, and sandstones of Paleo-
zoic origin (Hoffman and Alexander 1987). This
region of the Black Hills receives more precip-
itation in the form of snow (156 cm) and is cooler
(-58C) than more southern areas of the Black
Hills (Hoffman and Alexander 1987; NOAA
2017).
Ponderosa Pine (Pinus ponderosa) is the dom-
inant overstory tree species of the region; it
occurs in monotypic stands and is intermixed
with small stands of Quaking Aspen (Populus
tremuloides) and Paper Birch (Betula papyrifera)
(Mcintosh 1949; Orr 1959; Thilenius 1972;
Richardson and Petersen 1974; Hoffman and
Alexander 1987). Common plant species include
Kentucky Bluegrass (Poa pratensis), Timothy
(Phleum pretense), Smooth Brome (Bromus iner-
mis), sedges (Carex spp.), Western Wheatgrass
(Pascopyrum smithii), Prairie Dropseed (Sporobo-
lus heterolepis), fleabane (Erigeron spp.), and
yarrow (Achillea spp.) (Uresk and others 2009).
Additional ungulate species occupying the study
area included Mule Deer (Odocoileus hemionus),
White-tailed Deer (Odocoileus virginianus), and
Elk (Cervus elaphus). Potential species known to
predate on Bighorn Sheep occurring in the study
area included Mountain Lions (Smith and others
2014; Wilckens and others 2016), Coyotes,
Bobcats (Parr and others 2014), Bald Eagles
(Haliaeetus leucocephalus), and Golden Eagles
(Aquila chrysaetos). Potential species known to
transmit pathogens to Bighorn Sheep, including
Domestic Sheep and Goats (Capra hircus), were
located 5 km outside the study area.
Translocation and Data Collection
In February 2015, SDGFP and SDSU personnel
traveled to Hinton, Alberta, Canada to capture
and transport Bighorn Sheep to South Dakota.
Two sites in the Luscar Mine were baited with
FIGURE 1. The translocated Deadwood Bighorn
Sheep study area, including Domestic Sheep locations,
in the northern Black Hills of South Dakota.
224 NORTHWESTERN NATURALIST 99(3)
Alfalfa (Medicago sativa) hay for 1 wk prior to our
capture date. On 10 February 2015, modified 18
m x 18 m electromagnetic drop-nets were
constructed over bait sites, and the following
morning nets were used to capture Bighorn
Sheep (Jedrzejewski and Kamler 2004). Adult
male Bighorn Sheep were aged based on horn
annuli (Geist 1966) and adult females were aged
via tooth eruption and wear (Hemming 1969;
Krausman and Bowyer 2003). Twenty-one adult
females and 1 adult male Bighorn Sheep were
fitted with store-on-board global positioning
system (GPS; Model 2110D; 154–155 MHz) radio
collars (Advanced Telemetry Systems, Isanti,
MN). Two adult female Bighorn Sheep were
fitted with very-high-frequency (VHF; Model
2520B; 154–155 MHz) radio collars (Advanced
Telemetry Systems, Isanti, MN, USA). One
female Bighorn Sheep lamb and 1 male Bighorn
Sheep lamb were fitted with very high frequency
(VHF; Model M4200M; 154–155 MHz) expand-
able break-away radio collars (Advanced Telem-
etry Systems, Isanti, MN).
Uniquely identifiable ear tags were attached to
each individual Bighorn Sheep for future iden-
tification in the field. We collected blood samples
and swabbed nasal and pharyngeal passages for
disease testing. Swab and blood samples were
sent to Washington Animal Disease Diagnostic
Laboratory (WADDL), Pullman, Washington, to
test for the presence of Mycoplasma ovipneumo-
niae and pathogens related to pneumonia. Blood
samples were sent to The Holmes Research
Centre, University of Idaho, for selenium anal-
ysis. Blood serum for Brucella ovis,B. abortus,B.
suis, PI-3, Bovine Viral Diarrhea Virus, and
Bacillus thuringiensis serology was sent to USDA
APHIS National Veterinary Services Laborato-
ries. In addition, we administered (IM and
intranasally) a Mycoplasma ovipneumoniae vaccine
of the same strain (398) found in the nearest
Bighorn Sheep herd to our release site, Custer
State Park, to all Bighorn Sheep individuals. All
capture and handling methods were approved
by the South Dakota State University Institu-
tional Animal Care and Use Committee (Ap-
proval No. 14-096A).
Translocated Bighorn Sheep were released
approximately 3.5 km southwest of Deadwood,
South Dakota on private land. All radio-collared
Bighorn Sheep were located a minimum of 5
times per week post-release between February–
August 2015 and May–July 2016, and a mini-
mum of 3–4 times per week September 2015–
April 2016 and August–December 2016 using a
hand-held directional antenna and portable
receiver (model RA-23K, Telonics, Inc., Mesa,
AZ). Mortality events were generally located
within 12 h of receiving mortality signals from
collars; in the event Bighorn carcasses were
decayed or scavenged beyond recognition, sam-
ples were not collected, and individuals were
listed as ‘‘unknown’’ mortality events. Upon
finding Bighorn Sheep mortalities, we docu-
mented observations at the site, and carcasses
were transported to the SDGFP laboratory in
Rapid City, South Dakota, where necropsy was
performed and cause of death was determined.
The respiratory tract, including the lungs and
trachea, was sent to WADDL where comprehen-
sive testing for pathogen strains was conducted
using PCR (Besser and others 2013). Predation
events were documented by species of predator
via necropsy and investigation of the predation
site.
Data Analysis
We estimated survival of marked individuals
(n¼26) using the Kaplan-Meier method with
known-fate models in Program Mark (White and
Burnham 1999). Collared Bighorn Sheep encoun-
ter histories were converted to monthly encoun-
ter histories (n¼24) (White and Burnham 1999).
No individual Bighorn Sheep were censored in
the model, as each translocated individual was
identified as living or dead visually or via
telemetry during each encounter interval. GPS
collars fitted on live Bighorn Sheep released
automatically after approximately 700 d and
were recovered in the field, whereas GPS collars
fitted on Bighorn Sheep mortalities were recov-
ered at mortality sites; satellite location and time
data were offloaded from GPS collars. Mortali-
ties were assigned to the monthly encounter
interval based on GPS data or date of mortality
signal. We developed 9 a priori models to
investigate effects on Bighorn Sheep survival
(Table 1). Our variables included 2 temporal
seasonal models (winter season [October–Janu-
ary] versus remainder of year [February–Octo-
ber] and lambing season [May–June] versus
remainder of the year), age of individuals at
capture (adult versus subadult), year 1 (February
2015–January 2016) versus year 2 (February
2016–January 2017), regions (northern versus
WINTER 2018 225
WERDEL AND OTHERS:DEADWOOD BIGHORN SHEEP
southern), sex of individual, winter season-year
([October-January] and year), and month. These
variables were then compared to a constant
survival model.
Population size of the Deadwood Bighorn
Sheep herd was estimated weekly via telemetry
and visual identification. In lambing months
(May–June), Bighorn Sheep were located daily,
and a spotting scope was used to observe
neonate lambs from a distance .300 m. We
classified a ewe as having a lamb if it was
observed nursing or alone with a lamb, and
assumed lambs had died if they were no longer
observed with the ewe (Cassirer and Sinclair
2007). Lamb population numbers and recruit-
ment were recorded (May–June), and they were
monitored alongside collared adults throughout
the study period. Growth rates of the population
were calculated (February–January study peri-
ods) using geometric growth rate (k)and
instantaneous growth rate (r) models; k¼N
tþ1
/
N
t
and r¼ln(k).
RESULTS
In February 2015, we captured and radio
collared 26 Bighorn Sheep near Hinton, Alberta,
and translocated them to the Deadwood region
of the Black Hills, South Dakota. Among the 26
individuals, there were 23 adult females (.1.5
y), 1 adult male (.1.5 y), 1 subadult female
(,1.5 y), and 1 subadult male (,1.5 y). Of the 26
translocated individuals, none tested positive for
Mycoplasma ovipneumoniae prior to release. On 12
February 2015, the 26 Bighorn Sheep were
released onto private property 3.5 km southeast
of Deadwood, South Dakota.
Of the original 26 translocated Bighorn Sheep,
we documented a total of 19 mortality events,
February 2015–January 2017 (Table 1). Three
mortalities that resulted from a fall from a cliff
(adult female), a drowning (adult female), and a
broken neck (adult female) were categorized as
natural causes and accounted for 15.79% of
translocated Bighorn Sheep mortalities. Two
adult female mortalities resulted from collisions
with vehicles (10.53%), 1 on Interstate 90 and 1
on a county road. A single adult female died
within the first 3 wk post-release owing to stress
caused by capture and translocation (5.26%).
Four translocated Bighorn Sheep were eutha-
nized (21.05%): 1 adult male was euthanized
after moving to an area near Domestic Sheep 17
km north of the study area, near St. Onge, South
Dakota (evidence of pneumonia was not ob-
served at necropsy at WADDL in this lone
translocated breeding-age ram [.1.5 y]); and 3
adult females were euthanized based on symp-
toms consistent with pneumonia, including
lethargic behavior, consistent and prolonged
coughing, and drooping head and ears, and
evidence of pneumonia was observed at necrop-
sy examination at WADDL. Confirmed pneu-
monia accounted for the highest percentage
(42.11%) of mortalities of translocated Bighorn
Sheep (n¼8). If all confirmed pneumonia-
related mortalities are combined (n¼11), 57.9%
of all mortalities were a direct result of the
disease. Necropsies at the SDGFP laboratory
showed that mortalities that were pneumonia
related had varying stages of consolidated lung
tissue (lungs fused to chest cavity) and infection
(lesions exhibiting discolored discharge). One
adult female’s cause of death could not be
determined owing to scavenging of the carcass.
Winter season-year {S
oct-jan,year
} was consid-
ered the top model, of 9 total models evaluated,
for estimating annual translocated Bighorn
Sheep survival in the Deadwood region of South
Dakota (w
i
¼0.96). The remaining 8 models were
2DAIC
c
units from the top model, and the
weight of evidence supporting the top model
was 23.4 times greater than all other models
combined (Table 2). The top model, {S
oct-jan,year
},
continued to exhibit the lowest QAIC
c
even after
ˆ
c was artificially inflated to moderate (ˆ
c¼2.0,
QAIC
c
wt ¼0.72) and extreme dispersion (ˆ
c¼
3.0, QAIC
c
wt ¼0.48). Monthly survival for
October–January, year 1 (February 2015–January
2016) was 95.4% (95% CI ¼0.89–0.98; s
¯
x
¼0.021),
TABLE 1. Cause-specific mortality of translocated
Bighorn Sheep residing in the Deadwood region of
South Dakota, 2015–2017.
Cause-specific mortality n%
Natural causes 3 15.79
Falls from cliffs 1 5.26
Drowning 1 5.26
Broken neck 1 5.26
Capture stress 1 5.26
Vehicle collision 2 10.53
Euthanasia 4 21.05
Contact with Domestic Sheep 1 5.26
Pneumonia symptoms 3 15.79
Pneumonia 8 42.11
Unknown 1 5.26
Total 19 100
226 NORTHWESTERN NATURALIST 99(3)
and for all other months it was 99.4% (95% CI ¼
0.98–1; s
¯
x
¼0.003). Monthly survival for Octo-
ber–January, year 2 (February 2016–January
2017) was 82.9% (95% CI ¼0.72–0.90; s
¯
x
¼
0.047), and for all other months it was 97.6%
(95% CI ¼0.94–0.99; s
¯
x
¼0.011) (Fig. 2). Annual
survival rate of year 1 was 80.8% (95% CI ¼0.61–
0.92; s
¯
x
¼0.077) and annual survival rate of year
2 was 33.3% (95% CI ¼0.17–0.55; s
¯
x
¼0.103).
Survival rate of translocated Bighorn Sheep over
the course of the study was 30.7% (95% CI ¼
0.17–0.49; s
¯
x
¼0.085) (Fig.3).
The study began with a known number of 26
individual translocated Bighorn Sheep in a
closed, geographically isolated population post-
release. Each of the individuals was identifiable
by a radio collar and unique ear tag number.
Adult (.1.5 y) population, subadult (,1.5 y)
population, recruitment, deaths, total popula-
tion, and growth rates were recorded based on
weekly telemetry locations and visual monitor-
ing (Table 3). During May–June 2015, 15 lambs
were recruited into the population (11 females, 4
males; 65:100 lamb-to-ewe ratio; 100% lamb
survival [observed survival to 1 y]), whereas 5
lambs were recruited into the population during
the May–June 2016 lambing season (3 females, 2
males; 25:100 lamb-to-ewe ratio; 60% lamb
survival [observed survival to 1 y]). The year 1
(February 2015–January 2016) growth rate (k¼
1.38, r ¼0.322) was positive, whereas the year 2
(February 2016–January 2017) growth rate (k¼
0.667, r ¼–0.405) and rate for the entire study
period (February 2015–January 2017) (k¼0.92, r
¼–0.08) were negative.
DISCUSSION
Annual Bighorn Sheep survival and popula-
tion estimates documented in year 1 (February
2015–January 2016) showed that the translocated
Deadwood Bighorn Sheep herd was increasing
in size; there were no disease- or predation-
related mortalities documented during year 1,
which was inconsistent with previous studies in
populations established by translocation in the
Black Hills, SD (Smith and others 2014; Parr and
others 2018). Annual Bighorn Sheep survival
and population estimates documented in year 2
(February 2016–January 2016) reversed drasti-
cally from year 1, as we observed a sharp decline
TABLE 2. Models constructed a priori to evaluate influences on annual translocated Bighorn Sheep survival in
the Deadwood region of South Dakota, 2015–2017.
Model Description K
a
DAIC
c
AIC
c
w
i
Model
likelihood
{S
oct-jan, year
} Survival varied between winter
1
and rest of year
2
,
and between year 1
a
and year 2
b
3 0.0000 0.9590 1.0000
{S
oct-jan
} Survival varied between winter
1
and rest of year
2
2 6.3960 0.3917 0.0408
{S
t
} Survival varied by month 12 12.9050 0.0015 0.0016
{S
year
} Survival varied by year 2 16.4343 0.0003 0.0003
{S
may-june
} Survival varied between lambing season and non-
lambing season
2 21.4770 0.0000 0.0000
{S
constant
} Survival was constant 1 21.9561 0.0000 0.0000
{S
region
} Survival varied by region (Northern and Southern) 2 22.8282 0.0000 0.0000
{S
sex
} Survival varied by sex 2 22.9524 0.0000 0.0000
{S
agecapture
} Survival varied by age at capture [Adult (.1.5 y)
and Subadult (,1.5 y)]
2 23.4646 0.0000 0.0000
1
October–January
2
February–September
a
February 2015–January 2016
b
February 2016–January 2017
FIGURE 2. Survival estimates of translocated Big-
horn Sheep (n¼26) during winter and non-winter
periods 2015–2017, considering our top model
{S
oct-jan,year
}.
WINTER 2018 227
WERDEL AND OTHERS:DEADWOOD BIGHORN SHEEP
in the Deadwood herd size. This was due to
multiple factors, with a pneumonia event, which
was first observed 29 October 2016, being the
most severe. This type of quick and severe die-
off due to pneumonia has been documented as
early as 1924 (Marsh 1938) as well as in more
recent years (Cassirer and Sinclair 2007; Besser
and others 2012; Smith and others 2014).
Telemetry (3 to 7 d/wk), visual monitoring (3
to 7 d/wk), and GPS locations (every 5 h)
showed no indication of collared translocated or
uncollared Bighorn Sheep coming into contact
with Domestic Sheep in the area. However, the
Mycoplasma ovipneumoniae strain differed from
strains in known infected Bighorn Sheep popu-
lations within reasonable foray range (Black
Hills populations), so contact with a non-Big-
horn Sheep reservoir host was the presumptive
cause; Domestic Sheep and Goat locations were
in the vicinity (within 5 km) of the Deadwood
Bighorn Sheep home range. The Mycoplasma
ovipneumoniae strain attributed to the Deadwood
Bighorn Sheep herd die-off is one that had not
been previously documented in other Black
Hill’s Bighorn Sheep herds (SDGFP 2013; Smith
and others 2014; Parr 2015). One hypothesis that
could explain this pneumonia epizootic is that a
livestock trailer hauling Domestic Sheep to the
weekly, Thursday Sheep Sale at St. Onge, SD
(18.6 km from Deadwood, SD) came in close
proximity to Bighorn Sheep foraging in ditches
along a main road, and thus, transmitted the
disease without direct contact.
Survival rate of the collared Deadwood Big-
horn Sheep (n¼26) year 1 was 0.81, but declined
to 0.33 in year 2, which was lower than that
found by Parr and others (2018) who studied
Bighorn Sheep in the southern Black Hills; they
documented an annual ewe survival rate of 0.88
and ram survival rate of 0.85. The Deadwood
herd survival rate also was much lower than that
reported from other healthy Bighorn Sheep
populations (Jorgenson and others 1997 [0.95];
Singer and others 2000b [0.89]; Cassirer and
Sinclair 2007 [0.91]). Population estimates docu-
mented throughout the study period (February
2015–January 2017) showed declines in herd size
due to mortalities suffered during the last 4 mo
of the study. Parr and others (2018) found that a
Bighorn Sheep population in the southern Black
Hills was slightly increasing (k¼1.2) during
their study. An interesting finding in our study
was that there were no predation events.
Mountain lions were hypothesized to be the
greatest predation threat to the translocated
Deadwood Bighorn Sheep herd, based on
harvest and population data from SDGFP
(2014). Mountain Lion caches were found in
the immediate area of the Deadwood Bighorn
Sheep herd, but the contents of the caches
revealed that Mountain Lions had killed Mule
Deer, which occupied the same habitat (SDGFP
2013). We now hypothesize that Mule Deer
populations were at an adequate level to sustain
Mountain Lion populations, but if Mule Deer
populations decline or if Mountain Lions learn
skills for preying upon Bighorn Sheep (Jenks
2018), predation may begin to occur on resident
Bighorn Sheep. Previous studies in the Black
Hills have found that predation often occurs on
lambs and adults, even if the mortality was
TABLE 3. Population estimates of translocated Big-
horn Sheep in the Deadwood region of South Dakota,
2015–2017.
Category Year 1
a
Year 2
b
Release–
End of study
c
Adult Ewes 23 20 23
Adult Rams 1 1 1
Subadult Ewes 1 11 1
Subadult Rams 1 4 1
Recruitment 15 5 20
Deaths 5 17 22
Total 36 24 24
Geometric Growth
Rate (k)
1.38 0.667 0.92
Instantaneous Growth
Rate (r)
0.322 –0.405 –0.08
a
February 2015–January 2016
b
February 2016–January 2017
c
12 February 2015–20 January 2017
FIGURE 3. Kaplan-Meier survival curve of translo-
cated Bighorn Sheep (n¼26) throughout the study
period from February 2015 through January 2017.
228 NORTHWESTERN NATURALIST 99(3)
compensatory (Smith and others 2014; Parr
2015).
Visual observations of lambs with radio-
collared ewes may lead to an over-estimation
of true survival or recruitment rates (Smith and
others 2014). However, during the 1st year of our
study, intensive visual monitoring (5 to 7 times/
wk during the lambing period of May–June) of a
closed population with all individuals known,
led us to observe lamb survival at an unprece-
dented level of 100%, whereas previous studies
of pneumonia-free Black Hills’ Bighorn Sheep
populations have shown lamb survival only as
high as 44.7% (Parr and others 2018). In the Hells
Canyon region of Idaho, Oregon, and Washing-
ton, pneumonia-free populations had lamb
survival as high as 76% (Cassirer and Sinclair
2010). Similar to that documented by Parr (2015),
Bighorn Sheep in the Deadwood region of the
Black Hills tended to form groups based on lamb
survival; ewes that were without lambs (possi-
bly owing to undocumented lamb mortality)
made larger and more erratic movements,
whereas ewes with lambs formed nursery
groups near their respective lambing sites.
In July 2015, the lone translocated breeding-
age ram (.1.5 y) was euthanized after moving to
an area near domestic sheep 17 km north of the
study area and leaving only a subadult yearling
ram with the adult Bighorn ewes. However,
Bighorn Sheep, regardless of sex, have been
known to breed at 18 mo of age, so our
expectation was that the subadult ram would
become reproductively active before the No-
vember–December breeding season (Geist 1971).
Another obstacle to breeding in the 2015 season
was the separation of adult Bighorn ewes into 2
distinct ranges within the region; 6 ewes resided
near the Gilt Edge Mine, approximately 6 km
southeast of the larger subherd in the Deadwood
region, with little or no contact for much of the
year. Without the use of vaginal implant
transmitters (VITs), pregnancy rates for Novem-
ber–December 2015 could not be determined
until parturition in May–June 2016. Intensive
visual monitoring during the 2016 lambing
period (5 to 7 times/wk during May–June) led
us to estimate a lambing rate of 25:100 lamb-to-
ewe ratio (5 lambs of 20 adult ewes). This was a
significant decrease in lamb-to-ewe ratio from
2015 (65:100), most likely due to the presence of
a single young ram available to the Deadwood
Bighorn herd. Lamb survival during the summer
and autumn remained at 100%, but after our 1st
adult pneumonia event in October 2016, lamb
survival declined to 40% (2 lamb mortalities).
Carcasses of lambs were not found, but Smith
and others (2014) estimated a low lamb survival
rate of 2% for Bighorn Sheep in the eastern Black
Hills resulting from predation and disease. This
led us to hypothesize that pneumonia was the
most likely cause of lamb mortality in 2016.
Management Implications
Pneumonia pathogenic agents transmitted to
Bighorn Sheep may have been the greatest threat
to the survival of Bighorn Sheep in the Dead-
wood region. As the Deadwood Bighorn Sheep
herd is a relatively closed, geographically isolated
population in the Black Hills, it may be necessary
to move more than a single breeding-age male for
future translocations. Mountain Lion predation
wasnotafactorinsurvivalofBighornSheepin
the Deadwood region; however, that could
change in the future. It is recommended that a
more thorough investigation of the area for
Domestic Sheep and Goats be completed and
continued educational outreach to local Domestic
Sheep and Goat producers be implemented.
Attempts to reestablish Bighorn Sheep popula-
tions in areas with nearby Domestic Sheep and
Goats may be at a high risk for failure due to
pathogen transmission, and if there is no reason-
able likelihood of complete separation from
Domestic Sheep and Goats, translocations should
be avoided (WAFWA 2012).
ACKNOWLEDGEMENTS
Financial support for this project was provided by
Federal Aid to Wildlife Restoration administered
through South Dakota Department of Game, Fish
and Parks (Study Number 7556). We thank South
Dakota Department of Game, Fish and Parks, Civil Air
Patrol, Deadwood Police Department, Lawrence
County Sheriff’s Office, and private property owners
in the Deadwood area for their assistance and property
access. We thank A Ahlers, J Smith, and B Simpson for
their assistance with data analyses. We thank T Haffley,
K Cudmore, J Doyle, J Clark, and C Werdel for their
assistance with monitoring, capturing, and
euthanizing Bighorn Sheep during the study period.
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WINTER 2018 231
WERDEL AND OTHERS:DEADWOOD BIGHORN SHEEP
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The book covers population dynamics, diet, nutrition, diseases, behavior, and genetics of mountain lions occupying the Black Hills region. It explores the impact of a changing prey base on population growth and decline, movements within and away from the region, and hunting on the species; discusses interactions between the cats and livestock; and examines local people’s evolving perceptions of mountain lions. Provides a unique look into how a large, secretive predator recolonized an isolated region of North America.
Article
Longitudinal studies of survival are valuable because age-specific survival affects population dynamics and the evolution of several life history traits. We used capture-mark-recapture models to assess the relationship between survival and sex, age, population, year of study, disease, winter weather, and population density in two populations of bighorn sheep (Ovis canadensis) in Alberta, Canada. The Ram Mountain population, monitored for 20 yr, more than doubled in density; the Sheep River population, monitored for 13 yr, experienced a pneumonia epizootic. Yearling survival varied among years and was lower than that of older sheep of the same sex, except for yearling males at Ram Mountain. Yearling females at Ram Mountain were the only sex-age class exhibiting density dependence in survival. Senescence was evident for both sexes in both populations. Female survival from age 2 to age 7 was very high in both populations, but males aged 2 and 3 yr enjoyed better survival than males aged 4-6 yr. Our data support the suggestion that where hunters remove many males older than 5 yr of age, the natural mortality of males increases at 3-5 yr, possibly because young males suffer a mortality cost of participating in rutting activity. The decline in survival for sheep older than 7 yr was greater for males than for females. Survival was lower for males than for females, both among prime-aged sheep (0.896 vs. 0.939 at Sheep River; 0.837 vs. 0.945 at Ram Mountain) and among older sheep (0.777 vs. 0.859 at Sheep River; 0.624 vs. 0.850 at Ram Mountain), but not among yearlings. Survival of sheep aged 2-7 yr was not significantly different between the two populations. Winter weather did not affect survival. Survival of sheep 2 yr of age and older did not vary significantly between years, except at Sheep River where survival of prime-aged sheep of both sexes was lower in the year of the pneumonia epizootic. Studies of survival of mountain sheep based upon skull collections may have overestimated survival of young rams. Our results underline the need for accurate information on age-specific survival.
Article
Patterns of cementum, tooth succession, and external and internal horn annuli were studied in 129 specimens of Dall sheep (Ovis dalli). Fluoromicroscopy of annually produced cemental layers may be used to estimate age of all sheep older than 1 year. During the first 4 years of life age can be determined from the sequence of incisor replacement. Counts of annual horn increments provide a means of estimating age, but may be difficult to distinguish in older animals, particularly females.