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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
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Department of Natural Resource Management, South Dakota State University, Edgar S. McFadden Biostress
Lab, Brookings, SD 57007 USA
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164
South Dakota Game, Fish and Parks, 4130 Adventure Trail, Rapid City, SD 57702 USA
South Dakota Game, Fish and Parks, 13329 US Highway 16A, Custer, SD 57730 USA
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-
Current Address: Department of Horticulture and
Natural Resources, Kansas State University, Man-
hattan, KS 66506 USA;
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
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
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.
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
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.
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
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
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
and r¼ln(k).
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
} 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
¼0.96). The remaining 8 models were
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
continued to exhibit the lowest QAIC
even after
c was artificially inflated to moderate (ˆ
wt ¼0.72) and extreme dispersion (ˆ
3.0, QAIC
wt ¼0.48). Monthly survival for
October–January, year 1 (February 2015–January
2016) was 95.4% (95% CI ¼0.89–0.98; s
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
and for all other months it was 99.4% (95% CI ¼
0.98–1; s
¼0.003). Monthly survival for Octo-
ber–January, year 2 (February 2016–January
2017) was 82.9% (95% CI ¼0.72–0.90; s
0.047), and for all other months it was 97.6%
(95% CI ¼0.94–0.99; s
¼0.011) (Fig. 2). Annual
survival rate of year 1 was 80.8% (95% CI ¼0.61–
0.92; s
¼0.077) and annual survival rate of year
2 was 33.3% (95% CI ¼0.17–0.55; s
Survival rate of translocated Bighorn Sheep over
the course of the study was 30.7% (95% CI ¼
0.17–0.49; s
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.
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
oct-jan, year
} Survival varied between winter
and rest of year
and between year 1
and year 2
3 0.0000 0.9590 1.0000
} Survival varied between winter
and rest of year
2 6.3960 0.3917 0.0408
} Survival varied by month 12 12.9050 0.0015 0.0016
} Survival varied by year 2 16.4343 0.0003 0.0003
} Survival varied between lambing season and non-
lambing season
2 21.4770 0.0000 0.0000
} Survival was constant 1 21.9561 0.0000 0.0000
} Survival varied by region (Northern and Southern) 2 22.8282 0.0000 0.0000
} Survival varied by sex 2 22.9524 0.0000 0.0000
} Survival varied by age at capture [Adult (.1.5 y)
and Subadult (,1.5 y)]
2 23.4646 0.0000 0.0000
February 2015–January 2016
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
WINTER 2018 227
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,
Category Year 1
Year 2
End of study
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
February 2015–January 2016
February 2016–January 2017
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.
compensatory (Smith and others 2014; Parr
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
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).
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
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WINTER 2018 231
... We located all radio-collared bighorn sheep 5 −7 times/wk post release between February 2015 −August 2015 and May 2016 −July 2016, and > 3 times/wk September 2015 −April 2016 and August 2016 −December 2016 using a hand-held directional antenna and portable receiver (model RA-23K, Telonics, Inc., Mesa, AZ). GPS collars fitted on live bighorn sheep released automatically after ∼700 d and were recovered in the field, while GPS collars emitting a mortality signal were searched for in the field and recovered from deceased bighorn sheep (19 mortalities; Werdel et al. 2018 ); satellite location and time data were offloaded from GPS collars into ArcMap 10.3.1 (no locations were screened as 57 026 of 57 026 locations had < 10 horizontal dilution of precision [Lowrey et al. 2017] ; Environmental Systems Research Institute, Redlands, CA). ...
... Foraging sites of Deadwood bighorn sheep yielded mean herbaceous biomass (1 367.98 kg ·ha −1 ) and mean grass and forb cover (mean grass + mean forb cover = 37.17%), well above the 250 −300 kg ·ha −1 and 14% total grass and forb cover required by a bighorn sheep population of 125 individuals as outlined by Smith et al. (1991) . During February 2015-January 2016, the Deadwood bighorn sheep population had a geometric growth rate ( λ) of 1.38, including lamb survival of 100% ( Werdel et al. 2018 ). The population increased from 26 to 36 individuals, before a pneumonia outbreak (29 October 2016) severely diminished, and ultimately reversed growth ( λ = 0.67 during February 2016-January 2017 [Werdel et al. 2018] ). ...
... During February 2015-January 2016, the Deadwood bighorn sheep population had a geometric growth rate ( λ) of 1.38, including lamb survival of 100% ( Werdel et al. 2018 ). The population increased from 26 to 36 individuals, before a pneumonia outbreak (29 October 2016) severely diminished, and ultimately reversed growth ( λ = 0.67 during February 2016-January 2017 [Werdel et al. 2018] ). Although we can not extrapolate herbaceous biomass of foraging sites across the entire home ranges of individual bighorn sheep, it is likely that forage availability will not be a limiting factor to population growth as long as forage quality or availablity is not significantly altered. ...
Full-text available
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. We translocated 26 bighorn sheep from Al-berta, Canada to the northern Black Hills. We predicted that translocated bighorn sheep would exhibit similar resource use and selection as populations native to comparable habitats, specifically steep slopes with low overstory cover and high visibility. We used resource selection functions to estimate habitat selection by bighorn sheep and Robel pole and hand-clipped biomass to investigate the correlation between forage estimate methods. Bighorn sheep selected habitat types at varying levels, but were most strongly associated with barren and grassland landscapes while negatively associated with forest landscapes. Bighorn sheep had a positive association with slope and selected for fire-disturbed landscapes and elevation seasonally. Visual obstruction readings and herbaceous biomass at foraging sites (n = 78) were positively associated (r 2 = 0.62). Herbaceous biomass ranged from 302.07 to 2,487.43 kg ·ha −1. Foraging sites were typically located in areas with little overstory tree canopy cover (mean = 8.41%, standard error [SE] = 1.85), shorter distances to escape terrain (mean = 24.00 m, SE = 3.21), and low amounts of woody debris (mean = 0.25 kg ·ha −1 , SE = 0.07). The study area (Deadwood region of South Dakota) provided sufficient landscape attributes and herbaceous biomass to support the newly established bighorn sheep herd. Post-translocation assessments of resource use are crucial for evaluating conservation actions and potential success of future large mammal translocations.
... Since the 1950s, there have been >1,000 attempts to reintroduce bighorn sheep populations back to their historic range that have resulted in varying levels of success (Berger 1990;Singer et al. 2000;Hedrick 2014;Parr 2015;WAFWA 2015;Werdel et al. 2018). Reintroductions are generally focused in areas where bighorn sheep have been extirpated or where remnant populations require enhanced abundances or increases in genetic diversity to remain viable (Buechner 1960;Zimmerman 2008). ...
... All individuals were relocated using a hand-held directional antenna (Model RA-23K, Telonics, Inc., Mesa, AZ, U.S.A.) and portable receiver (Model TR-2, Telonics, Inc.). Mortality events were located within 12 hours of receiving mortality signals from collars; however, if decayed or significantly scavenged, we did not collect samples and we recorded the mortality cause as unknown (5.26% [1/19] of mortality events; Werdel et al. 2018). We transported recovered bighorn sheep carcasses to the South Dakota Game, Fish and Parks (SDGFP) laboratory in Rapid City, South Dakota, and performed a necropsy to determine mortality cause. ...
... Our prior study documented 19 mortalities (7 of 26 translocated bighorn sheep survived the study period), 57.9% (n = 11) were pneumonia related, within the translocated Deadwood bighorn sheep herd between February 2015 and January 2017 (Werdel et al. 2018). The only adult ram was euthanized due to presumed contact with domestic sheep; however, the ram displayed no signs of poor condition, and post-mortem analyses revealed that it was PCR and cELISA negative for M. ovipneumoniae (Table S1). ...
Full-text available
Bighorn sheep (Ovis canadensis) were once extirpated from the Black Hills region of South Dakota, USA, mirroring declining populations throughout North America. Since the 1960s, several reintroductions have occurred in the Black Hills to reestablish populations with varying success. We translocated 26 bighorn sheep from Alberta, Canada to the Black Hills (February 2015) to restore bighorn sheep to their historic range. Due to prior examinations of cause-specific survival, subsequent genetic diversity and disease prevalence were required to evaluate success of the restoration effort. We measured a mean allelic diversity of 5.23 (SE=0.44 [mean number of alleles]) and an observed heterozygosity of 0.71 (SE=0.06; expected = 0.64 ± 0.05) in the translocated individuals. Translocated bighorn sheep tested negative for Mycoplasma ovipneumoniae at capture. An autogenous vaccine was administered prior to release in an attempt to safeguard the translocated bighorn sheep from infection with a strain known to be resident in adjacent bighorn sheep populations. However, the year following the translocation, a different strain of M. ovipneumoniae was associated with a pneumonia outbreak that resulted in 57.9% mortality. Our results suggest that allelic diversity and heterozygosity were sufficient for long-term herd establishment, reducing the potential for founder effects. However, the This article is protected by copyright. All rights reserved. Deadwood bighorn sheep disease and diversity overwhelming mortality associated with pneumonia, via the transfer of M. ovipneumoniae from an unknown source, limited the success or our reintroduction efforts. Successful attempts to restore bighorn sheep to their historic ranges must consider and mitigate potential routes for M. ovipneumoniae transmission pre-and post-reintroduction.
... These sheep had been vaccinated against Mycoplasma spp. but encountered a different strain (Mycoplasma ovipneumoniae) upon release, and therefore were susceptible to disease [24,25]. ...
... Where details were available, the projects had varying degrees of a DRA. This included some studies having knowledge of specific pathogens that may be encountered [17,18,[31][32][33][34], vaccination [17,24,25,32], anthelmintic treatment [17,35], quarantine [32,35], pathogen testing [36], and veterinary examination [17,35,37]. ...
Full-text available
Although translocation projects have been instrumental in the supplementation or restoration of some wild populations, they also carry a large risk of disease transmission to native and translocated animals. This study systematically reviewed conservation translocation projects to identify projects that met the criteria for a translocation significant disease incursion (TSDI), whereby the translocation resulted in negative population growth rates or the failure of populations to grow due to an infectious disease—either in the native or translocated species. In doing so, risk factors for these incidents could be identified. Analysis of the resulting 30 TSDIs demonstrated that there was equal representation of TSDIs using wild-caught and captive-bred animals. Additionally, the type of pathogen predisposed in a TSDI was more likely a result of the animal group translocated (e.g., fungal pathogens were more likely to be detected in amphibian translocations) and it was nearly five times more likely for a disease to be encountered by a translocated species than for a disease to be introduced to a native population. However, there are numerous project-specific predisposing factors for TSDIs, and therefore it is essential that future translocation projects conduct thorough disease risk analysis as well as report their outcomes for the benefit of their own and future translocations.
... Movement for each individual bighorn sheep, isolating only locations obtained from year 1 (Feb 2015-Jan 2016) and year 2 (Feb 2016-Jan 2017) time periods, were plotted using the "move" package in Program R (Werdel et al. 2018; R Core Team 2020); movement statistics (i.e., travel distance, maximum distance, minimum distance) also were derived. Visual and statistical [travel distance (ANOVA)] comparisons were made between the separate time periods to test the hypothesis that translocated Deadwood bighorn sheep herd would pioneer a greater distance (i.e., utilize exploratory movements in excess of core home-range) in year 1 than year 2. ...
... The translocated Deadwood bighorn sheep herd was not observed as migratory. However, the only adult male bighorn sheep that was originally translocated did show signs of differing movement during the summer, but was euthanized, due to potential contact with domestic sheep, ending data collection (Werdel et al. 2018); this type of movement by adult rams has been documented by DeCesare and Pletscher (2006) and Parr (2015). Seasonal movement was observed during the lambing season, which was predicted due to previous bighorn sheep research in the southern Black Hills (Parr 2015). ...
Full-text available
Ungulate species have consistently been a major focus of reintroductions to their native ranges. Bighorn sheep (Ovis canadensis) are an ecologically sensitive species, and have experienced population declines throughout their historic range; bighorn sheep inhabited the Black Hills region of South Dakota but were extirpated from the area due to anthropogenic impacts in the early 1900s. To continue to restore populations to the area, we translocated 26 bighorn sheep from Alberta, Canada to the Deadwood Region of the Black Hills. Bighorn sheep were fitted with VHF or GPS collars and monitored throughout the duration of the study (Feb 2015–Jan 2017). Our objectives were to evaluate movement patterns post-release of bighorn sheep in the translocated Deadwood bighorn sheep herd. We utilized 3 types of home-range analyses based on collar data; kernel density estimation (KDE), minimum convex polygon (MCP), and Brownian Bridge Movement Models (BBMM) were used to estimate home-ranges year 1, year 2, and for the duration of the study. Home-range size utilizing KDE (95%; \(\overline{x}\) = 41.41 km2, SE = 10.50), minimum convex polygon (95%; \(\overline{x}\) = 55.73 km2, SE = 15.04), and BBMM (95%; \(\overline{x}\) = 32.95 km2, SE = 4.67) differed among methods. Year 1 home-range sizes (95% BBMM; \(\overline{x}\) = 40.01 km2) were larger than year 2 (95% BBMM; \(\overline{x}\) = 4.08 km2) home-range sizes. Travel distances were also larger in year 1 (\(\overline{x}\) = 431.80 km) than year 2 (\(\overline{x}\) = 368.77 km). Our results indicate that after an acclimation period, which included individual dispersal, the translocated Deadwood bighorn sheep herd settled into smaller home-ranges near the release site.
... Regardless of management goals, practitioners should rigorously evaluate post-translocation metrics (e.g. survival, space use) to assess the effectiveness of their efforts (Jachowski et al. 2016, Lehrer et al. 2016, Werdel et al. 2018, Berger-Tal et al. 2019. ...
Full-text available
Muskrats Ondatra zibethicus are semiaquatic herbivores experiencing long-term and widespread population declines across North America. Translocation may be a viable tool to bolster or reestablish local populations; however, subsequent effects of translocation on muskrats are unknown. We live-trapped and translocated radiomarked muskrats (n = 65) during the summers of 2018–2019 in Voyageurs National Park, MN, USA and assessed post-translocation effects on weekly survival probabilities and space-use patterns. We did not observe homing behavior, though individuals moved an average of 2.2 km (SE = 0.30 km) from release sites and established home ranges within ∼8 days (SE = 1.16 days) post-translocation. Weekly post-translocation survival probabilities (0.95, SE = 0.001) and average home-range sizes (2.52 ha, SE = 0.44 ha) were similar to other studies of non-translocated muskrats. Our most-supported known-fate survival model revealed muskrats using beaver Castor canadensis lodges had greater weekly survival probabilities. Additionally, weekly muskrat survival varied between years suggesting a positive response to a novel soft-release technique applied in 2019. Our study provides the first empirical assessment of translocation effects on muskrats and suggests translocation may be effective for establishing or enhancing local muskrat populations. Additionally, our study suggests beaver lodges may confer fitness benefits to sympatric muskrats particularly during dispersal.
Full-text available
Bighorn sheep (Ovis canadensis) were re- introduced to the Black Hills of South Dakota and Wyoming beginning in 1965. Various pneumonia outbreaks caused populations to decline periodically, resulting in little to no lamb recruitment. An isolated population of bighorn sheep resides on Elk Mountain along the South Dakota-Wyoming border in the southern Black Hills. We estimated population size, survival, and recruitment rates of bighorn sheep on Elk Mountain by radio-collaring adult and neonatal sheep from 2012 to 2014. Overall annual ewe survival was 88.1% (se = 0.05), ram survival was 85.1% (se = 0.10), and 26 wk lamb survival was 44.7% (se = 0.09). Recruitment through 26 wk averaged 35% (SD = 0.02) across years. Population estimates for the 3 y were 80 (se = 0.58), 100 (se = 2.42), and 115 (se = 6.89) individuals, respectively. The Elk Mountain bighorn sheep herd experienced lamb survival and recruitment during 2012-2014; coupled with minor predation losses and a lack of deadly pneumonia, this herd is expected to continue to grow in size.
Full-text available
Recent recolonization of mountain lions (Puma concolor) into the Little Missouri Badlands of North Dakota, has led to questions regarding the potential impacts of predation on prey populations in the region. From 2012 to 2013, we deployed 9 real-time global positioning system (GPS) collars to investigate mountain lion feeding habits. We monitored mountain lions for 1,845 telemetry-days, investigated 506 GPS clusters, and identified 292 feeding events. Deer (Odocoileus spp.) were the most prevalent item in mountain lion diets (76.9%). We used logistic regression to predict feeding events and size of prey consumed at an additional 535 clusters. Our top model for predicting presence of prey items produced a receiver operating characteristic (ROC) score of 0.90 and an overall accuracy of 81.4%. Application of our models to all GPS clusters resulted in an estimated ungulate kill rate of 1.09 ungulates/week (95% CI = 0.83–1.36) in summer (15 May ‒ 15 November) and 0.90 ungulates/week (95% CI = 0.69–1.12) in winter (16 November ‒ 14 May). Estimates of total biomass consumed were 5.8 kg/day (95% CI = 4.7–6.9) in summer and 7.2 kg/day (95% CI = 5.3–9.2) in winter. Overall scavenge rates were 3.7% in summer and 11.9% in winter. Prey composition included higher proportions of nonungulates in summer (female = 21.5%; male = 24.8%) than in winter (female = 4.8%; male = 7.5%). Proportion of juvenile ungulates in mountain lion diets increased during the fawning season (June ‒August) following the ungulate birth pulse in June (June–August = 60.7%, 95% CI = 43.0–78.3; September–May = 37.2%, 95% CI = 30.8–43.7), resulting in an ungulate kill rate 1.61 times higher (1.41 ungulates/week, 95% CI = 1.12–1.71) than during the remainder of the year (0.88 ungulates/week, 95% CI = 0.62–1.13). Quantifying these feeding characteristics is essential to assessing the potential impacts of mountain lions on prey populations in the North Dakota Badlands, where deer dominate the available prey base and mountain lions represent the lone apex predator.
Full-text available
Bighorn sheep (Ovis canadensis) were re-introduced into the Black Hills, South Dakota, U.S.A. in 1965. To date limited information exists concerning vital rates of this population. From 2010 to 2013, we estimated survival and cause-specific mortality of 55 adult female bighorn sheep in three herds in the east-central Black Hills. We documented 21 mortalities. Of those, pneumonia (19%) and predation (19%) accounted for most known causes of mortality; however, we were unable to ascertain cause of death for 47.6% of mortalities. We used a known fate analysis in Program MARK to estimate monthly survival; our best approximating model indicated survival differed during May-Jun compared with the remainder of the year. Monthly survival estimates for May-Jun were 0.95 (95% CI = 0.91-0.97) compared with 0.99 (95% CI = 0.98-0.99) for Jul-Apr, and overall annual survival was 0.81 (95% CI = 0.72-0.87). We found little support for the hypothesis that survival was influenced by body mass or nutritional condition (ingesta-free body fat). Our results indicated disease, predation, and other factors predisposing ewes to mortality, especially during and shortly after parturition, were contributors to the current demographic status of this population.
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.
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.
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.