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The Gordian knot of mountain lion predation and bighorn sheep: Mountain Lion Predation and Bighorn Sheep

Authors:
  • New Mexico Department of Game and Fish

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The objective of this review is to generate a synthesis of research conducted on predation of bighorn sheep (Ovis canadensis) and to suggest directions for future research relative to current knowledge gaps and a novel hypothesis. This review is primarily based on literature from the last 60 years on desert bighorn sheep (O. c. nelsoni), Rocky Mountain bighorn sheep (O. c. canadensis), and mountain lion (Puma concolor) predation. Although, many predators kill bighorn sheep, only mountain lions are currently considered to be the primary proximate cause of mortality for many bighorn sheep populations. The ultimate cause of this phenomenon has vexed wildlife managers for >40 years. There are 3 primary reasons for increased predation on bighorn sheep by mountain lions. First, there is an increased presence of mountain lions in habitats where they were historically absent or rare because of the expansion of mule deer (Odocoileus hemionus) following the extensive conversion of fire-maintained grasslands to shrublands in the late-1800s. Second, is the extirpation of the 2 dominant apex carnivores (wolves [Canis lupus] and grizzly bears [Ursus arctos]) during this same time period and a hypothesized numerical response of mountain lions to those extirpations. Finally, the response of mountain lions to the cessation of >70 years of intensive predator control has often resulted in unsustainable mountain lion-bighorn sheep ratios, especially for desert bighorn sheep. Additionally, the effect of mountain lion predation is exacerbated by declines in bighorn sheep that do not result in declines in mountain lions because of their ability to prey switch to mule deer, elk (Cervus canadensis), or domestic cattle; kleptoparasitism of mountain lions kills, by ursids and canids, resulting in higher kill rates for mountain lions; and a possible ecological trap where adaptations derived over evolutionary time are no longer adaptive because of human-induced changes in the sympatric apex predator guild. Control of mountain lions, when mountain lion-ungulate ratios are high, might be required to protect small or endangered bighorn sheep populations, and to produce bighorn sheep for restoration efforts. © 2017 The Wildlife Society.
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Invited Paper
The Gordian Knot of Mountain Lion
Predation and Bighorn Sheep
ERIC M. ROMINGER,
1
New Mexico Department of Game and Fish, Santa Fe, NM 87504, USA
ABSTRACT The objective of this review is to generate a synthesis of research conducted on predation of
bighorn sheep (Ovis canadensis) and to suggest directions for future research relative to current knowledge
gaps and a novel hypothesis. This review is primarily based on literature from the last 60 years on desert
bighorn sheep (O. c. nelsoni), Rocky Mountain bighorn sheep (O. c. canadensis), and mountain lion (Puma
concolor) predation. Although, many predators kill bighorn sheep, only mountain lions are currently
considered to be the primary proximate cause of mortality for many bighorn sheep populations. The ultimate
cause of this phenomenon has vexed wildlife managers for >40 years. There are 3 primary reasons for
increased predation on bighorn sheep by mountain lions. First, there is an increased presence of mountain
lions in habitats where they were historically absent or rare because of the expansion of mule deer (Odocoileus
hemionus) following the extensive conversion of fire-maintained grasslands to shrublands in the late-1800s.
Second, is the extirpation of the 2 dominant apex carnivores (wolves [Canis lupus] and grizzly bears [Ursus
arctos]) during this same time period and a hypothesized numerical response of mountain lions to those
extirpations. Finally, the response of mountain lions to the cessation of >70 years of intensive predator
control has often resulted in unsustainable mountain lion-bighorn sheep ratios, especially for desert bighorn
sheep. Additionally, the effect of mountain lion predation is exacerbated by declines in bighorn sheep that do
not result in declines in mountain lions because of their ability to prey switch to mule deer, elk (Cervus
canadensis), or domestic cattle; kleptoparasitism of mountain lions kills, by ursids and canids, resulting in
higher kill rates for mountain lions; and a possible ecological trap where adaptations derived over evolutionary
time are no longer adaptive because of human-induced changes in the sympatric apex predator guild. Control
of mountain lions, when mountain lion-ungulate ratios are high, might be required to protect small or
endangered bighorn sheep populations, and to produce bighorn sheep for restoration efforts. Ó2017 The
Wildlife Society.
KEY WORDS apparent competition, bighorn sheep, ecological trap, kleptoparasitism, mountain lion, Native
American fire, predation, predator control, predator-prey ratio.
Predation on bighorn sheep (Ovis canadensis), specifically
mountain lion (Puma concolor) predation on isolated
populations of bighorn sheep, has hindered restoration
efforts for bighorn sheep in western North America. This
review paper synthesizes our current knowledge and includes
a novel hypothesis for the ultimate cause of high mountain
lion predation that has confounded wildlife managers for >4
decades. This review is derived primarily from historical
literature published in the last 60 years on desert bighorn
sheep (O. c. nelsoni), Rocky Mountain bighorn sheep (O. c.
canadensis), and mountain lion predation.
Predation has a profound influence on prey population
dynamics in many ecosystems. Laboratory, mesocosm, or
natural experiments have assessed the role of predation on
non-ungulate prey including relationships between starfish
(Pisaster spp.) and tidal pool prey (Paine 1969), mites
(Typhlodromus occidentalis) and mite prey (Tarsonemus
pallidus and Eotetranychus sexmaculatus; Huffaker 1958),
mesocarnivores and waterfowl (Garrettson and Rohwer
2001), weasels (Mustela nivalis) and voles (Microtis agrestis;
Graham and Lambin 2002), mountain lions and porcupines
(Erethizon dorsatum; Sweitzer et al. 1997), lynx (Lynx
canadensis) and snowshoe hares (Lepus americanus; Krebs
et al. 1995), and numerous other species. Hairston et al.
(1960:424) noted “herbivores are seldom food-limited and
appear most often to be predator-limited.” Excluding
anthropogenic associated mortality, only disease has the
potential for greater population-level consequences on prey
populations (Pedersen et al. 2007).
The scientific literature on predation and ungulates is
replete with evidence of the depressive effects that carnivores
can have on ungulate populations (Gasaway et al. 1992,
Harrington et al. 1999, Hayes et al. 2003, Wittmer et al.
2005, Bergerud et al. 2007). For example, some species of
African ungulates increased 7 times following the removal
Received: 10 October 2016; Accepted: 5 October 2017
1
E-mail: eric.rominger@state.nm.us
The Journal of Wildlife Management; DOI: 10.1002/jwmg.21396
Rominger Mountain Lion Predation and Bighorn Sheep 1
of apex carnivores and all prey species <150 kg declined to
near pre-removal densities after those predators were
reestablished (Sinclair et al. 2003).
Asymptotic densities of ungulate populations, including
bighorn sheep, on predator-free islands and in predator-free
enclosures are examples of the profound influence the
absence of predation can have on prey density. In North
America, maximum ungulate densities in those settings are
remarkably similar across an array of ecosystems and study
area sizes ranging from 2.5–8,000 km
2
(McCullough 1979,
Bowyer et al. 1999, Bergerud et al. 2007, Simard et al. 2010,
Rominger 2015). In predator-free environments the median
maximum density of deer-size ungulates is approximately 35
individuals/km
2
and compared to adjacent mainland areas
with predators, ungulate densities are generally an order of
magnitude, or more, greater (Rominger 2015).
High ungulate densities in the absence of predation have
been documented in many cases for decades (Matthews
1973, New Mexico Department of Game and Fish
[NMDGF], unpublished data) and for 80–130 years in
thecaseoftheSlateIslands,Ontario, Canada, Anticosti
Island, Quebec, Canada, and Antelope Island, Utah, USA
(Wolfe and Kimball 1989, Potvin et al. 2003, Bergerud
et al. 2007) despite dramatic changes in vegetation
composition. In other northern hemisphere predator-
free islands, the non-irruptive mean ungulate density is
like that reported on North American islands (Kaji et al.
2004). Density of tropical fauna is also 10 to 100 times
greater on tropical predator-free islands compared with
adjacent mainland densities, which mirrors the ratio of
ungulate densities on temperate islands to adjacent
mainlands (Terborgh et al. 2001).
The predator evasion strategy of bighorn sheep relies on the
combination of keen eyesight to detect predators at distance
and the ability to navigate steep terrain and outmaneuver
predators following visual detection (Geist 1999). Sexual
segregation of female and juvenile bighorn sheep, from male
bighorn sheep, is hypothesized to be related to anti-predator
behavior that includes proximity to steep escape terrain
(Bleich et al. 1997). Both strategies are more effective, and
therefore likely to have evolved, in response to coursing
predators (e.g., wolves [Canis lupus]; Festa-Bianchet 1991).
These strategies are less effective against a stalking predator
(e.g., mountain lions).
Bighorn sheep-predator relationships are associated with
potential proximate and ultimate causes. High mountain lion
predation on bighorn sheep, particularly desert bighorn
sheep and Sierra Nevada bighorn sheep (O. c. sierrae) has
been the proximate factor hindering restoration in many
historical ranges (Wehausen 1996, Hayes et al. 2000, Kamler
et al. 2002, Rominger et al. 2004). High mountain lion
predation on bighorn sheep, seen since the 1970s, appears to
be related to the cessation of intensive predator control used
during much of the twentieth century. This release of
mountain lions from predator control has resulted in
increased mountain lion-bighorn ratios that can be
unsustainable based on native ungulate density, especially
for desert bighorn sheep (Rominger 2013).
The ultimate cause of high mountain lion predation on
bighorn sheep appears to be related to a restructuring of the
apex predator guild following the extirpation of wolves and
grizzly bears (Ursus arctos; Young and Goldman 1944, Brown
1985), major shifts in biotic communities (Berger and
Wehausen 1991, McPherson 1995), and the associated
restructuring of the ungulate guild across much of western
North America. This restructuring has been primarily
influenced by the cessation of widespread Native American
burning and hunting (Turner 1991, Kay 1995, Stewart
2002), the introduction of livestock and feral equids (Berger
and Wehausen 1991, Brown 1994), and the resulting
expansion of mule deer (Odocoileus hemionus) and mule deer
habitats.
Other ecological factors affecting predation and bighorn
sheep include apparent competition (Rominger et al. 2004,
Johnson et al. 2013), specialist predators (Ross et al. 1997,
Logan and Sweanor 2001, Knopff and Boyce 2007, Knopff
et al. 2010), kleptoparasitism (Elbroch et al. 2015),
vulnerability of small populations (Berger 1990), subsidized
predators (Rominger et al. 2004), indirect effects of
predation (Bourbeau-Lemieux et al. 2011), and declining
native prey (Unsworth et al. 1999). The extirpation of wolves
and grizzly bears from the predator guild associated with
bighorn sheep resulted in mountain lions becoming the
primary bighorn sheep predator. This human-induced
change might have resulted in an ecological trap
(Dwernychuk and Boag 1972, Schlaepfer et al. 2002).
Continued restoration of wolf and grizzly bear populations
throughout Rocky Mountain and desert bighorn sheep
habitat will add complexity associated with multi-predator,
multi-prey systems (Knopff and Boyce 2007, Kortello et al.
2007, Knopff et al. 2010, Ruth et al. 2011) compared to many
systems that only have had mountain lions as a resident apex
carnivore for most of the last century.
Virtually all predators, sympatric with bighorn sheep,
ranging in size from gray fox (Urocyon cinereoargenteus)to
grizzly bear, have been documented to prey upon bighorn
sheep (Sawyer and Lindzey 2002) and except for foxes, have
been documented to prey on adults and juveniles. Although
smaller predators (e.g., coyotes [Canis latrans], bobcats [Lynx
rufus], and golden eagles [(Aquila chrysaetos]), and less
cursorial predators (e.g., black bear [U. americanus] and
grizzly bear) are likely more effective predators of neonates,
mountain lions have been documented as the primary
predator of lambs (Parsons 2007, Smith et al. 2014, Karsch
et al. 2016).
The consensus in the earliest review of the effects of
predation on desert bighorn sheep was that no predators had
population-level consequences (Desert Bighorn Council
[DBC] 1957). At the inaugural DBC meeting, a special
session on predation concluded that bobcats and golden
eagles were the primary predators of desert bighorn sheep but
that neither species limited population demographics (DBC
1957). Most biologists working on desert bighorn sheep
thought that mountain lion numbers were so low, and the
predator-control programs so strict (private and government
year-round trapping and hunting, bounties, poisons), that
2 The Journal of Wildlife Management 9999()
mountain lions simply could not induce population declines.
The first monograph and 2 of the earliest books on Rocky
Mountain and desert bighorn sheep ecology (Buechner 1960,
Geist 1971, Monson and Sumner 1980) were written during
a period when mountain lions were unprotected, or just
recently protected by law, and wolves had been extirpated
from all bighorn sheep habitats in the conterminous United
States (Young and Goldman 1944). Mountain lion predation
was not considered to be an important influence on bighorn
sheep population dynamics.
In contrast, 5–6 decades later, a different predator-
management paradigm, with mountain lions protected
throughout the United States (except TX) and Canadian
provinces, has shifted our interpretation of the consequences
of predation. The demographic recovery of mountain lions in
virtually all bighorn sheep ranges, and the advent and use of
radio-telemetry to assess mortality causes, has resulted in
multiple examples of population-level effects of mountain
lion predation on bighorn sheep (Harrison and Hebert 1988,
Wehausen 1996, Hayes et al. 2000, Rominger et al. 2004,
Festa-Bianchet et al. 2006). In a recent review, Sawyer and
Lindzey (2002) determined that mountain lions were capable
of depressing bighorn sheep populations and numerous
publications have corroborated that conclusion (Kamler et al.
2002, McKinney et al. 2006, Foster and Whittaker 2010,
Brewer et al. 2013, Johnson et al. 2013).
CHANGES IN THE PREDATOR-PREY
COMMUNITY
Predation on bighorn sheep hypothetically has been
influenced by a change in the apex predator guild following
the extirpation of wolves and grizzly bears and a change in
the ungulate guild following the conversion of much of
western North America from a grassland ecosystem
maintained with fire by Native Americans to a shrub-
dominated ecosystem. Changes in the ungulate guild are
primarily related to the extensive range expansion of mule
deer throughout large portions of bighorn sheep range
(Berger and Wehausen 1991, Turner 1991, McPherson
1995, Kay 1995, Stewart 2002).
Changes in Predator Guild
Grizzly bear and wolf distribution overlapped nearly all
Rocky Mountain bighorn sheep range and some desert
bighorn ranges (Young and Goldman 1944, Lamb et al.
2017). These 2 predators were absent only from the most
xeric parts of Mexico, western Arizona, California, and
Nevada (Young and Goldman 1944, Lamb et al. 2017). The
extirpation of wolves (Young and Goldman 1944) and near
extirpation of grizzly bears (Brown 1985, Lamb et al. 2017)
is well documented. Mountain lions are subordinate to
wolves and bears (Boyd and Neale 1992, Kortello et al.
2007, Ruth et al. 2011, Elbroch et al. 2015) and much like
the well documented response of subordinate coyotes to the
absence of wolves (Berger and Gese 2007, Merkle et al.
2009), mountain lions almost certainly have responded
numerically to competitive release from these 2 dominate
carnivores. Evidence of this subordination is the observation
that when pursued by hounds, mountain lions in North
America will climb trees. In South America, where
mountain lions did not evolve with a large canid predator,
they do not climb trees when pursued by hounds (B. M.
Jansen, Arizona Game and Fish Department [AZGFD],
personal communication.). Although the total cost to
mountain lions of sympatry with wolves has not been
assessed, it is hypothesized that interactions could affect
reproduction, survival rates, habitat selection, and home
range size (Kortello et al. 2007, Ruth et al. 2011). Mountain
lion survival was negatively affected by increasing annual
wolf use, wolves were responsible for 15% of adult mountain
lion deaths, and wolf predation decreased annual kitten
production 10–39% (Ruth et al. 2011).
Anecdotal evidence suggests that mountain lions and
coyotes were rare or absent where grizzly bears and wolves
occurred in New Mexico (Barker 1953, Stevens 2002).
Stevens (2002) hunted grizzly bears, black bears, and
mountain lions with dogs throughout the late 1800s, in
the portion of New Mexico that is now the Gila Wilderness,
but only mentioned 2 mountain lions in his book. In 1882, a
Professor Dyche from the University of Kansas came to New
Mexico to collect grizzly bears in what is now the Pecos
Wilderness. Using a tree blind and a deer for bait, Dyche
reported bobcats and foxes but not a single coyote in his
diary, although they became common after the turn of the
century following the extirpation of wolves (Barker 1953).
Extirpation of wolves and grizzly bears was facilitated by
intensive predator control. Private predator control efforts
began in the western United States soon after livestock was
introduced following the end of warfare with Native
Americans. In 1914, following a Congressional appropria-
tion, federal agencies employed 300 predator control agents
to protect livestock and remnant wild ungulate populations
(Brown 1992). Control efforts included year-round trapping,
poisoning, hunting with hounds, denning, and bounties paid
from private and government sources (Buechner 1960,
Brown 1992).
Xeric ecoregions with sufficient numbers of deer to
maintain resident mountain lions, but without wolves or
grizzly bears, presumably functioned much like systems
where high mountain lion predation on bighorn occurs
today. Historical accounts suggest that native ungulate
densities may have been low in multi-prey ecosystems with
sympatric mountain lions as the primary apex predator. As
Charles Sheldon embarked on a bighorn sheep hunt into
Mexico in 1915, his guide remarked that he had recently
been to the Sierra Pintas in Arizona and “lions are numerous
there but sheep are scarce” (Sheldon 1979:66). During the
1907 William Hornaday expedition from Tucson, Arizona
to the Pinacate Mountains in Sonora, Mexico, a single adult
deer was seen in a trip that lasted more than 30 days
(Hornaday 1908).
Mountain lions may have been less common historically
because of interspecific competitors (Stevens 2002, Riley
et al. 2004, Wittmer et al. 2005) and a much more limited
distribution of mule deer (Berger and Wehausen 1991,
Potter 1995, Heffelfinger and Messmer 2003). Although
Rominger Mountain Lion Predation and Bighorn Sheep 3
mountain lion abundance might have been briefly released
following the extirpation of wolves, >70 years of intensive
predator control kept numbers low. Quantifying abundance
of mountain lions is difficult (Logan and Sweanor 2001) and
there are no reliable estimates from periods of intensive
predator control. Bounty records from 1902–1906 in
Montana indicate that bounties paid for wolves out-
numbered those paid for mountain lions by >30:1. By
region, there was an inverse relationship between the number
of wolves and mountain lions for which a bounty was paid
suggesting that in areas where wolves were prevalent,
mountain lions were rare (Riley et al. 2004).
Changes in Prey Guild
Grasslands were maintained across western North America
with fire by Native Americans for millennia (Turner 1991,
Kay 1995, McPherson 1995, Stewart 2002). Shrubs, which
are the primary forage of mule deer, were an inconspicuous
component of desert grasslands prior to 1880 (McPherson
1995). Reports of mule deer were rare in the diaries of early
travelers and were reported to be a minor component of
Native American diets (Berger and Wehausen 1991, Potter
1995, Heffelfinger and Messmer 2003, Kay 2007). The
landscape conversion, of historical grasslands to shrub or
chaparral, was influenced by grazing of excessive numbers of
livestock and feral equids (Berger and Wehausen 1991). This
conversion resulted in range expansion of mule deer and
concomitantly the presence of mountain lions (Berger and
Wehausen 1991). This conversion of grasslands to chaparral
and shrublands occurred throughout bighorn sheep ranges in
western North America. Range expansion of mountain lions
following invasion by white-tailed deer (Odocoileus virgin-
ianus) into areas of clear-cut old-growth forests converted
to shrub-dominated habitats also has been documented
(Compton et al. 1995, Wittmer et al. 2005).
The 500,000-km
2
Great Basin ecoregion is hypothesized
to have been void of deer and mountain lions because grass-
dominated basin and range habitats, maintained by burning
by Native Americans, did not support deer (Berger and
Wehausen 1991). The Great Basin contains extensive
bighorn sheep habitat and pronghorn (Antilocapra americana)
and bighorn sheep were likely the primary ungulates present
in this vast landscape. Therefore, bighorn sheep in the Great
Basin may have encountered little predation by mountain
lions just 125 years ago. Niche separation between
pronghorn and bighorn sheep would have resulted in this
ecosystem functioning much like a single-prey system.
Analysis of Native American diets at 2 pueblo sites in New
Mexico reported the ratio of pronghorn specimens to deer
specimens was 25:1 and 79:1, respectively (Potter 1995).
Mountain lions are most effective at limiting bighorn sheep
populations when they are able to prey switch onto deer,elk, or
cattle and there is little evidence that mountain lions can limit
bighorn sheep populations without alternative prey (Berger
and Wehausen 1991, Wehausen 1996). Resident mountain
lions were undocumented in bighorn sheep habitat of the
Providence and New York Mountains, California, United
States, until the introduction of mule deer (R. A. Weaver,
California Department of Fish and Wildlife, personal
communication). Mountain lion predation is rare in the
most xeric mountainranges without sympatric deeror livestock
(Berger and Wehausen 1991, Cronin and Bleich 1995).
THE PARADOX OF MOUNTAIN LION
DENSITY
Regardless of the mechanisms that have resulted in the
predator-prey guilds present today, it is the current ratio of
mountain lions to native ungulate populations that appears to
influence the primary proximate cause of mortality for bighorn
sheep. Following decades of intensive predator control,
mountain lions have increased numerically and in distribution
(Fecske et al. 2011, Knopff et al. 2014). Predator control across
North America was initially directed primarily toward wolves;
however,theemphasis switched to mountainlions,black bears,
and coyotes following the near-extirpation of wolves. Some
states paid higher bounties for female mountain lions to
incentivize population reduction (Buechner 1960). Until the
cessation of large-scale predator control, mountain lion
predation on bighorn sheep populations was insignificant
(DBC 1957).
In a review of 12 studies assessing the effects of sport
hunting on mountain lions, the range of densities was
1.1–7.1 mountain lions/100 km
2
, although the low density
does not include subadults or kittens (Cooley et al. 2011).
A density of 1–3 mountain lions/100 km
2
when coupled
with a standard ungulate kill rate (Wilckins et al. 2016)
mayhaveaprofoundinuenceonungulatepopulation
dynamics (Table 1).
Global positioning system (GPS) collaring of mountain lions
has allowed for a refinement of kill rates by visiting waypoint
clusters associated with kills and most studies have confirmed
that mountain lions kill about 1 ungulate/week (Anderson and
Lindzey 2003, Knopff et al. 2009, Wilckins et al. 2016). This
value is used as the mean for calculating the number of ungulate
kills/100 km
2
with the 95% confidence interval for a high and
low kill rate (Table1; Wilckins et al. 2016). At a high densityof
3 mountain lions/100 km
2
and a high kill rate of 1.1ungulate/
week, there would be a predicted 172 kills/100 km
2
annually
(Table 1). Most smalldesert bighorn sheep populationsin New
Mexico were predicted to go extinct with 5% additive
mountain lion mortality (Fisher et al. 1999). For 172 kills to
be 5% of a wild ungulate population, the density required
would be 3,440 ungulates/100 km
2
. At a low density of 1
mountain lion/100 km
2
and a low kill rate of 0.9 ungulate/
week there would be 47 kills annually (Table 1). For 47 kills to
be 5% of a wild ungulate population, the density required
would be 940 ungulates/100km
2
. Both numbers are essentially
1–2 orders of magnitude greater than currently estimated
ungulate densities in desert bighorn sheep ranges in New
Mexico (Bender et al. 2012, Rominger 2013). This is the
paradox that influences high mountain lion predation in desert
bighorn sheep ranges. Cunningham et al. (1999) estimated
that 44% of mountain lion dietary biomass was comprised of
livestock at an Arizona study area. The fact thatmountain lions
are a subsidized predator (Soule et al. 1988) is a partial
explanation for their ability to persist despite low native
4 The Journal of Wildlife Management 9999()
ungulate densities (Cunningham et al. 1999, Rominger et al.
2004).
In the Fra Cristobal Mountains, New Mexico, mountain
lion control conducted from 1999 until 2013 resulted in the
highest estimated ungulate density of any desert mountain
range in the state (New Mexico Department of Game and
Fish [NMDGF], unpublished data). The combined bighorn
sheep and mule deer density is approximately 400/100 km
2
(NMDGF, unpublished data). From 2003 to 2013, an
average of 3.3 mountain lions were killed annually on the
107-km
2
mountain range (NMDGF, unpublished data).
However, even at this high ungulate density, 2 resident
mountain lions could potentially kill nearly 25% of the
resident ungulates annually.
A long-term mountain lion study on the San Andres
Mountains, New Mexico documented 1.72–4.25 mountain
lions/100 km
2
including adults, subadults, and cubs. This
study was completed in 1995 just as high mountain lion
predation adversely affected mule deer density and was
also the predominant mortality cause associated with the
biological extinction of desert bighorn sheep (Logan and
Sweanor 2001, Rominger and Weisenberger 2000). Follow-
ing this study, mule deer density declined to one of the
lowest ungulate densities reported in North America
with an estimated 10–12 deer/100 km
2
(Bender et al.
2012, Rominger 2013). Although mountain lion density
in the San Andres Mountains is currently unknown, they
persist in this habitat despite a very low deer density. There
has been no discernable recovery of mule deer in >20 years.
DIRECT PREDATION
Although predation by mountain lions had been anecdotally
noted by several authors (Leopold 1933, DBC 1957,
Blaisdell 1961), it was not until the earliest stages of the
restoration of desert bighorn sheep in Texas that high
mountain lion predation was documented to cause popula-
tion declines (Kilpatric 1976). In rapid succession, other
western states and provinces began documenting instances of
high mountain lion predation (Table 2). Most early data are
reported as a percentage of radio-collared bighorn sheep
killed annually (Mu~noz 1982, Harrison and Hebert 1988,
Creeden and Graham 1997, Ross et al. 1997).
Table 1. Kills as a percentage of 3 hypothetical deer-size ungulate-prey population densities using 3 values of mountain lion density and 3 values of kill rates
(e.g., low lion density [1.0] low kill rate [0.9] 52 weeks ¼47 kills/annually). The final column is number of deer-size ungulates/100 km
2
required for the
number of kills to be a 5% mortality rate (e.g., 47 kills/5100) ¼940.
Mountain lion
density/
100 km
2a
Mountain lion weekly
kill rates
b
(no. prey)
No.
annual
kills
Annual % mortality
c
at 50 prey/100 km
2
Annual % mortality
c
at 100 prey/100 km
2
Annual % mortality at
200 prey/100 km
2
No./100 km
2
if %
mortality ¼5%
1 0.9 47 94 47 24 940
1 1.0 52 >100 52 25 1,040
1 1.1 57 >100 57 28 1,140
2 0.9 94 >100 94 47 1,880
2 1.0 104 >100 >100 52 2,080
2 1.1 114 >100 >100 57 2,280
3 0.9 140 >100 >100 70 2,800
3 1.0 156 >100 >100 78 3,120
3 1.1 172 >100 >100 86 3,440
a
These values lower than most values in Cooley et al. (2011).
b
Mean kill rate 95% confidence intervals from Wilckins et al. (2016).
c
>100 indicates the estimated annual kill exceeds population size.
Table 2. Examples of high mountain lion predation on bighorn sheep (bhs) in western North America.
Location Year Citation Specifics
TX 1975 Kilpatric (1976, 1982) 21 bhs killed inside captive breeding facility by mountain lions at
Black Gap State Wildlife Area; the wild population estimated
to have declined from 20 to <10
NM 1979 Mu~noz (1982) 9 of 25 (36%) bhs killed by mountain lions in 14 months
NM 1980–1989 Hoban (1990) 22 of 43 bhs mortalities attributed to mountain lion predation
NM 1996–1997 Rominger and Weisenberger (2000) Bhs decline from 25 to 1 resulting in biological extinction.
Mountain lion predation the primary cause of death
BC 1986–1988 Harrison and Hebert (1988) 2 female mountain lions kill a minimum of 21 bhs in 14 months
CO 1995 Creeden and Graham (1997) 5 of 14 (36%) radio-collared bhs killed by mountain lions within
12 months
AB 1985–1994 Ross et al. (1997) 13% of winter bhs population killed; 1 female mountain lion
killed 9% of total population and 26% of lambs in 1 winter
OR 1995–2002 Foster and Whittaker (2010) Hart Mountain bhs herd declined from 600 to 125 with
mountain lion predation the primary cause of mortality
CA 1997–1999 Schaefer et al. (2000) Mountain lion predation cause of 75% of bhs mortality
CA 1976–1988 Wehausen (1996) 49 bhs documented killed by mountain lions without telemetry
AZ 1979–1997 Kamler et al. (2002) In meta-analysis of 365 translocated bhs, 66% of mortality was
mountain predation
Rominger Mountain Lion Predation and Bighorn Sheep 5
The development of survival models (Heisey and Fuller
1985, White and Burnham 1999) that incorporate data from
telemetrically monitored bighorn sheep, allow researchers to
calculate cause-specific mortality rates (CSMR; Table 3).
Mountain lion-specific mortality rates of adult bighorn sheep
have been as high as 0.26 (Hayes et al. 2000), 0.29 (Kamler
et al. 2002), and 0.31 (Goldstein and Rominger 2012) in
some ranges. Statewide lion-specific mortality rates for
desert bighorn sheep in New Mexico between 1992 and 2002
were 0.16 (Goldstein and Rominger 2012) and 88% of New
Mexico desert bighorn sheep populations went extinct or
declined to <10 females during this period.
The high mortality rates on state-endangered desert
bighorn, attributed to mountain lion predation, in New
Mexico during the 1990s were unsustainable and caused
populations to decline rapidly (Goldstein and Rominger
2012). However, substantially lower mountain lion mortality
rates are projected to be detrimental to the persistence of
small populations of bighorn sheep. A Vortex model for
state-endangered desert bighorn sheep in New Mexico
predicted that all extant populations had a 100% probability
of extinction with just 10% mountain lion predation added
to baseline non-predation demographic parameters (Fisher
et al. 1999). Initial population sizes of these small herds
ranged from 10–120 and just a 5% mountain lion predation
rate induced an extinction probability of 0.82–1.0 for 6 extant
herds (Fisher et al. 1999).
Following the initiation of mountain lion control in desert
bighorn sheep ranges in New Mexico, numbers increased from
<170 in 2001 to >1,100 in 2016 (Fig. 1; Ruhl and Rominger
2015). After 31 years on the New Mexico threatened and
endangered species list, desert bighorn sheep were delisted
in 2012 and returned to a state-protected game species
(Rominger et al. 2009, Goldstein and Rominger 2013).
Predation is the dominant cause of mortality for ungulate
neonates (Smith et al. 1986, Scotton 1998, Gustine et al.
2006, Quintana et al. 2016). Predation caused 82% and 86%
of mortality of desert bighorn sheep lambs in 2 studies in
New Mexico (Parsons 2007, Karsch et al. 2016). In both
studies, mountain lions were the apex predator.
Although wolves are currently considered to be a predator
of minor consequence, as mountain lions were in 1957,
wolves are still recolonizing many Rocky Mountain bighorn
sheep ranges and have just begun to re-occupy historical
desert bighorn sheep ranges in Arizona and New Mexico.
The ecological relationship between wolves and mountain
lions is not well understood (Husseman et al. 2003, Kortello
et al. 2007, Ruth et al. 2011, Krawchuck 2014) and research
has been primarily conducted in ecosystems recently
recolonized by one or both predators, or where both
carnivores have responded to less intensive predator control
(Knopff and Boyce 2007, Kortello et al. 2007, Ruth et al.
2011). Most of these studies have reported mountain lions
to be subordinate to wolves resulting in usurpation of kills,
direct mortality of adult and juveniles, and constriction of
home ranges (Boyd and Neale 1992, Kortello et al. 2007,
Ruth et al. 2011).
In North American ecosystems occupied by Dall’s sheep
(O. dalli dalli), the primary predator is the wolf and there is
little evidence of consistent population-level consequences
of predation (Barichello and Carey 1988, Hayes et al. 2003),
although Bergerud and Elliot (1998) reported improved
recruitment of Stone’s sheep (O. d. stonei) following the
reduction of wolf numbers in British Columbia. Barichello
and Carey (1988) reported no evidence that a substantial
reduction in wolf density influenced demographics of Dall’s
sheep. However, Arthur and Prugh (2010) reported high
Table 3. Cause-specific mortality rates (CSMR) on bighorn sheep (bhs) attributed to mountain lion predation in western North America.
Location Year Citation Mortality rates
CA 1988–1995 Wehausen (1996) CSMR due to mountain lions was 0.38
AZ 1979–1997 Kamler et al. (2002) In meta-analysis of 365 translocated bhs, the highest CSMR due to mountain
lions was 0.29
AZ 1993–1996 Bristow and Olding (1998) CSMR due to mountain lions was 0.12 for females and 0.15 for males
NM 1992–2000 Rominger et al. (2004) CSMR due to mountain lions was 0.13 for males and 0.09 for females in
desert habitat
OR 2004 Foster and Whittaker (2010) CSMR due to mountain lions for 44 radio-collared bhs was 0.17 for males
and 0.10 for females
AB/MT 1983–2003 Festa-Bianchet et al. (2006) During years of high mountain lion predation, the CSMR due to mountain
lions was 0.26 for males and 0.32 for females
CA 1992–1998 Hayes et al. (2000) CSMR due to mountain lions for 113 radio-collared bhs ranged between 0.08
and 0.26
Figure 1. Desert bighorn sheep population estimates, New Mexico,
1980–2016. From 1979–1999, there were 253 desert bighorn sheep released
into wild populations. From 2000–2016, there were 274 desert bighorn
sheep released into wild populations. Mountain lion control began in 1999 in
all endangered desert bighorn sheep herds when statewide population
estimates declined to <170 in 6 herds.
6 The Journal of Wildlife Management 9999()
levels of Dall’s sheep lamb mortality by coyotes, which are
hypothesized to have increased because of wolf control.
Coyotes are reported to kill adult and juvenile ungulates
(Hass 1989, Kelley 1980) and were the second-most
important predator of juvenile desert bighorn sheep after
mountain lions in the Peloncillo Mountains, New Mexico
(Karsch et al. 2016). Coyotes may be more effective predators
than wolves on wild sheep neonates (Arthur and Prugh 2010)
and the extirpation of wolves has resulted in a competitive
release of coyotes (Berger and Gese 2007). Hebert and
Harrison (1988) reported coyote predation as a major source
of lamb mortality in British Columbia, Canada, and that
predator control targeting coyotes was responsible for a 2–
2.5-fold increase in lamb:female ratios. Bobcats are reported
to kill adult and juvenile ungulates (Kelley 1980, DeForge
2002); however, there is little evidence that they have
population-level effects on bighorn sheep populations.
Bobcats were not confirmed to have killed desert bighorn
sheep lambs in the 2 New Mexico studies (Parsons 2007,
Karsch et al. 2016).
Most bighorn sheep herds are comprised of <100
individuals (Berger 1990) and therefore may be more
vulnerable to extinction (Berger 1990, Fisher et al. 1999),
although Wehausen (1999) found less support for a strong
population size effect on extinction probability. High levels
of predation can cause the extirpation of small isolated
populations of bighorn sheep (Rominger and Weisenberger
2000), woodland caribou (Rangifer tarandus; Kinley and
Apps 2001), and other species (Williams et al. 2004).
However, bighorn sheep populations >100 also have been
documented to decline substantially, with mountain lion
predation the primary cause of mortality (Wehausen 1996,
Hayes et al. 2000, Foster and Whittaker 2010).
Bighorn sheep populations with sympatric deer have been
documented to decline to low density, with mountain lion
predation the primary mortality factor (Wehausen 1996,
Foster and Whittaker 2010, Rominger 2013). This apparent
competition in multiple-prey systems was first described by
Holt (1977) and has been documented in bighorn sheep
populations (Rominger et al. 2004, Johnson et al. 2013) and
other ungulates (Bergerud and Elliot 1986, Harrington et al.
1999, McLellan et al. 2010, Wittmer et al. 2014). For Sierra
Nevada bighorn sheep, the more common prey species is
mule deer (Johnson et al. 2013); however, in most desert
bighorn sheep habitats in Arizona and New Mexico,
domestic cattle, usually juveniles, are also alternative prey
(Cunningham et al. 1999, Rominger et al. 2004).
The usurpation of mountain lion kills by interspecific
competitors, primarily bears or wolves, can influence
predation dynamics. In Colorado and California, mountain
lion kill rates increased 48% in the presence of sympatric
black bears because of kleptoparasitism, with bears detected
at 48–77% of mountain lion kills (Elbroch et al. 2015).
Although mountain lions may occasionally kill small black
bears at cache sites, it appears that mountain lions generally
depart permanently following the arrival of larger black bears
(Elbroch et al. 2015). Wolves were documented to usurp
12% and scavenge 28% of mountain lion kills during a 4-year
period (Kortello et al. 2007). In southern British Columbia,
where wolves and grizzly bears were extirpated, or greatly
reduced, mountain lions are the dominant predator of
woodland caribou (Compton et al. 1995, Kinley and Apps
2001, Wittmer et al. 2005). However, in north-central
British Columbia, where wolves and grizzly bears persist,
mountain lions are not the dominant predator (Wittmer
et al. 2005).
After work by Ross et al. (1997) that documented high
mortality on a wintering bighorn sheep herd by an individual
mountain lion, it has been debated whether most predation
on bighorn sheep is a function of specialist mountain lions.
Although, specialist predators exist (Ross et al. 1997, Logan
and Sweanor 2001, Knopff and Boyce 2007), other data
suggest that most sympatric mountain lions will kill bighorn
sheep. In the Peninsular Ranges of California, 18 of 23
individually identified mountain lions were associated with
bighorn sheep kills (Ernest et al. 2002) and in the Fra
Cristobal Mountains, New Mexico 16 of 18 radio-collared
mountain lions either killed or attempted to kill desert
bighorn sheep (NMDGF, unpublished data).
The predator-evasion strategy of bighorn sheep is far more
effective against a coursing predator than a stalking predator
(Festa-Bianchet 1991) and the abrupt removal of wolves and
widespread replacement by mountain lions may have resulted
in an evolutionary trap where past selection pressures shaped
cue-response systems that were adaptive but no longer are in
the face of human-induced changes. Additionally, the sexual
segregation behavior of bighorn sheep might be associated
with the potential for an ecological trap. Mortality rates for
female bighorn sheep, attributed to mountain lion predation
can be as high or higher than those for males, suggesting the
benefit of this sexual segregation strategy is not particularly
effective against mountain lion predation (Krausman et al.
1989, Hayes et al. 2000, Kamler et al. 2002, Festa-Bianchet
et al. 2006).
DISCUSSION
Recent studies throughout western North America provide
evidence that direct predation by mountain lions is a primary
proximate mortality factor of bighorn sheep. The increase in
mountain lion predation on bighorn sheep has followed the
demographic recovery of mountain lion populations follow-
ing the cessation of intensive predator control efforts. The
recovery of mountain lions was preceded by expansion of
their primary prey, mule deer, following the vast conversion
of grasslands that had been maintained with fire by Native
Americans. This shift in the mountain lion prey guild
allowed for range expansion of mountain lions into habitats
where wolves and grizzly bears have been extirpated. The
combination of restructured predator-prey guilds and
elimination of Native American fire and hunting has resulted
in bighorn sheep with sympatric mountain lion densities
unlikely to have occurred previously.
Additionally, livestock and feral equids responsible for
conversion of grasslands contribute to the alternative prey-
base for mountain lions. In ecosystems with low densities of
native prey, cattle subsidize mountain lion populations and
Rominger Mountain Lion Predation and Bighorn Sheep 7
may comprise >40% of the biomass in mountain lion diets,
precluding a decline in mountain lion numbers despite
declining native ungulate populations (Cunningham et al.
1999, Rominger et al. 2004). Feral equids are also reported to
subsidize mountain lion populations, although they are much
less numerous than cattle (Berger 1986, Turner et al. 1992,
Knopff and Boyce 2007). Low densities of native ungulates
are correlated with increased depredation of livestock by
felids and canids (Brown 1992, Khorozyan et al. 2015).
The intensity of mountain lion predation has been reported
to be nearly continuous in some ecosystems and more pulse-
like in other ecosystems (Ross et al. 1997, Rominger et al.
2004). Because bighorn sheep density is rarely but a fraction
of that observed on predator-free islands and predator-free
enclosures, most predation is considered additive mortality,
especially at low bighorn sheep densities. The stalking
hunting style of mountain lions is hypothesized to result in
more prime-age bighorn sheep kills compared to the effect
of a coursing hunting style (e.g., wolves), which exposes
compromised individuals. Additionally, the encroachment
of woody vegetation due to the exclusion of fire for more
than a century has enhanced stalking cover for mountain
lions (Wakelyn 1987).
Increased mountain lion predation and related declines in
New Mexico desert bighorn sheep populations have been
correlated with declines in sympatric mule deer. These
populations declined sharply in the mid-1990s and there has
been no discernable recovery in the last 20 years (Rominger
and Weisenberger 2000, Bender et al. 2012, NMDGF,
unpublished data). Observations of deer during helicopter
surveys in the San Andres Mountains were as high as 150
deer/hour and have declined to <5.5 deer/hour for all
bighorn sheep surveys flown since 1996 (NMDGF,
unpublished data). The estimated deer density in the San
Andres has declined to 0.08–0.11 mule deer/km
2
, making
this one of the lowest densities of North American ungulates
ever reported (Bender et al. 2012, Rominger 2013). Because
of this low density, there has been no deer hunting on the
entire 8,300-km
2
White Sands Missile Range, New Mexico
since 1999. Similarly, low mule deer observation rates have
been recorded in all other desert bighorn sheep surveys in
New Mexico for the last 20 years (NMDGF, unpublished
data). However, it was the ratio of mountain lions to these
very low-density ungulates that precluded recovery and has
required mountain lion control to increase desert bighorn
sheep numbers.
Declines in bighorn sheep populations, due to mountain
lion predation, have been reported for nearly every state and
province where this species occurs. There is little evidence
that these populations recover in the absence of predator
control. One exception appears to be the federally endan-
gered Peninsular bighorn sheep population. Although this
herd is still listed as endangered, it has increased from
approximately 275 (Rubin et al. 1998) to approximately 980
(Botta 2011) without mountain lion control. Peninsular
bighorn sheep have an elevational niche separation from
mule deer that use habitat at higher elevations in the
Peninsular Ranges (Hayes et al. 2000), much like the niche
separation of pronghorn and bighorn sheep in the Great
Basin (Berger and Wehausen 1991). Thus, mountain lions
hunting in low-elevation desert bighorn habitat have
virtually no opportunity to prey switch onto deer without
vacating bighorn sheep habitat.
Management of predation deemed excessive relative to
bighorn sheep population objectives generally involves lethal
predator control. Controlling apex carnivores is much more
controversial than culling mesocarnivores (Reiter et al. 1999,
Rominger 2007) despite documented success in the
protection and recovery of endangered species (Hecht and
Nickerson 1999, Rominger et al. 2009, Johnson et al. 2013,
Hervieux et al. 2014).
Predator control is used by most western state and
provincial wildlife agencies to protect endangered ungulate
species (Hervieux et al. 2014) and big game populations
(Rominger 2007). Predator control to protect translocated
desert bighorn was first advocated by Wilson et al. (1973)
and has been used to aid the restoration of bighorn sheep
in New Mexico, California, Texas, Arizona, Utah, and
elsewhere (Rominger 2007). High levels of mountain lion
predation associated with desert bighorn sheep trans-
locations and some Rocky Mountain bighorn sheep trans-
locations (Krausman et al. 1999, Rominger et al. 2004,
McKinney et al. 2006) can be reduced by removing resident
mountain lions prior to translocation. After multiple failed
translocations due to mountain lion predation, NMDGF no
longer translocates desert bighorn sheep without a pre-
treatment mountain lion control program to reduce the
density of resident mountain lions, usually beginning 3–4
months prior to translocation.
Following the extirpation of desert bighorn sheep in the
Catalina Mountains, Arizona in the 1980s, desert bighorn
sheep were released into historical habitat in 2013
(Krausman 2017). The initial translocation, done without
a pre-treatment removal of resident mountain lions, had
high mortality with mountain lionskilling15of30radio-
marked bighorn sheep within 4 months. Post-release
control of offending mountain lions resulted in the lethal
removal of 7 mountain lions. To date, mountain lions have
killed a minimum of 27 of 86 radio-marked bighorn sheep
from 3 releases. In the absence of mountain lion control,
this attempted restoration of a native faunal component
would have almost certainly failed.
Ernest et al. (2002) modeled predator control management
options to mitigate mountain lion predation and determined
that for populations or subpopulations with <15 females,
range-wide control (habitat control) of mountain lions was
the most effective paradigm. At higher female numbers, less
strict take of mountain lions was recommended (e.g., only
remove offending mountain lions [kill-site removal]).
However, this model assumes that a documented offending
mountain lion will be removed prior to making additional
kills. A large data set from NMDGF suggests this is unlikely
and offending mountain lions were taken at <20% of
bighorn sheep kills (Rominger et al. 2011). During a period
of range-wide mountain lion control, 68 mountain lion-
killed bighorn sheep with very high frequency (VHF)
8 The Journal of Wildlife Management 9999()
radio-collars were documented. However, only 13 (19%)
offending mountain lions were culled.
The 2 primary reasons mountain lions were not culled were
the bighorn sheep kill was not detected and located prior to
the mountain lion departing (59% of all kills) and the
mountain lion was present but missed at the kill site (54% of
attempted removals were unsuccessful because the mountain
lion did not step into snare, substrate was not conducive to
snare placement, hounds were unable to tree or bay mountain
lion). Although sample sizes were substantially reduced, the
data set was partitioned between attempts to snare offending
mountain lions and attempts to hound-hunt offending
mountain lions. Use of hounds was successful in 5 of 14
attempts, whereas use of snares was successful in 8 of 14
attempts (Rominger et al. 2011). Culling offending
mountain lions in the Catalina Mountains, Arizona
restoration project has been successful in 6 of 15 attempts
and this higher success rate is attributed to the use of GPS
collars that alerted managers to mountain lion kills more
quickly than VHF radio-collars (B. D. Brochu, AZGFD,
personal communication).
Trapping and translocation is the primary management
tool used to reestablish bighorn sheep populations into
unoccupied habitats (Foster 2004). Currently, most bighorn
sheep used for translocation come from mountain lion-free
islands (e.g., Tiburon Island, Sonora, Carmen Island, Baja
California Sur, MX; Wild Horse Island, MT, USA,
Antelope Island) or predator-free enclosures (e.g., Red
Rock, NM, USA and Pilares, Coahuila, MX). Very few
desert bighorn sheep populations with uncontrolled sympat-
ric mountain lions produce surplus bighorn sheep for
translocations.
Restoration of natural grasslands, maintained by frequent
fires, at scales that would substantially reduce deer numbers is
unlikely to bea near-term management option. However, most
state and provincial agencies have developed habitat manage-
ment plans to reduce woody vegetation to increase bighorn
habitat, and potentially reduce stalking habitat for mountain
lions. Although, mountain lion predation seems to be lowest
in single-prey systems in themost xeric habitats, most bighorn
sheep currently occur in habitats with multiple sympatric
ungulates. It is hypothesized that high levels of alternative
buffer prey are preferable to low-density buffer prey when
habitats have high mountain lion density.
Kill rates may increase substantially in ecosystems with
high levels of kleptoparasitism and if deemed excessive,
population reduction of kleptoparasites, specifically bears,
would be a novel management action. The cumulative
effects of predation on all sex and age classes of a bighorn
sheep population must be recognized. Total predation in
ecosystems with a diverse predator guild may have a much
more profound influence on bighorn sheep demography;
therefore, wildlife managers must decide on the appropriate
response relative to management needs (Griffin et al. 2011).
Small, isolated bighorn sheep herds, reduced to very low
numbers by predation, will require human-mediated
translocations to mitigate genetic loss and demographic
declines.
Factors that influence rates of mountain lion predation
should be examined experimentally to enable managers to
better understand this complex system that appears to be
substantially altered by anthropogenic causes. Experiments
should be designed and conducted in bighorn sheep herds
that are large enough to sustain high levels of predation
without the need to manipulate mountain lion numbers
during the experiment. Understanding the role of alternative
prey, including livestock, will be a potential research
direction. Understanding the influence of wolf restoration
on bighorn sheep and mountain lions, particularly the effect
on recruitment of adult female mountains lions, will be
important. Because mountain lions are relatively long-lived,
this research should be conducted over long periods
following the reestablishment of wolves.
MANAGEMENT IMPLICATIONS
Productive bighorn sheep populations are required for
restoration via translocation, sport hunting, and endangered
species recovery. Management practices to decrease moun-
tain lion densities that adversely affect bighorn sheep
populations can be ideally addressed via sport harvest levels
regulated by state wildlife agencies. In habitats or states (e.g.,
CA) where sport harvest does not meet management
objectives, facilitated mountain lion control may be required
to prevent population declines of bighorn sheep. Removal of
resident mountain lions, prior to translocation of desert
bighorn sheep, has increased the probability of successful
restoration (Rominger et al. 2009).
There is still the potential that bighorn sheep can remain a
viable faunal component in the North American west. If the
public and wildlife managers are interested in keeping and
restoring bighorn to their native ranges for viewing, hunting,
and as source populations for recovery in landscapes that have
been anthropogenically altered, difficult decisions will have
to be made. Continued research on predation and other
ecological factors will aid in the conservation of this species.
ACKNOWLEDGMENTS
I thank H. H. Sawyer and F. G. Lindzey for their review of
predation and bighorn sheep in 2002, J. L. Davis and J. D.
Wehausen for stimulating discussions on California moun-
tain lion and bighorn sheep ecology. V. W. Anglin, J. F.
Anglin, A. Ford (deceased), W. D. Glenn, S. C. Harvill, K.
Glenn-Kimbro, and L. D. Lindbeck for their considerable
knowledge of lion hunting. A. R. E. Sinclair and V. Geist
provided insight on predation. B. D. Brochu provided
insight on the high mountain lion predation in the current
restoration effort in the Catalina Mountains, Arizona. H. U.
Wittmer provided insight on the kleptoparasitism and
apparent competition literature. M. C. Chitwood provided
insight on the ecological trap literature. R. A. Weaver
(deceased), A. V. Sandoval, and R. Valdez provided
discussions on desert bighorn sheep ecology. State and
provincial biologists that have shared their knowledge
include S. B. Bates, V. C. Bleich, C. E. Brewer, T. L.
Carlsen, E. F. Cassirer, V. L. Coggins, S. C. Cunningham,
Rominger Mountain Lion Predation and Bighorn Sheep 9
D. L. Heft, H. B. Ernest, C. L. Foster, E. J. Goldstein, F.
Hernandez, A. H. Hubbs, M. C. Jorgensen, C. P. Lehman,
A. A. Munig, S. M. Murphy, T. D. Nordeen, R. W.
Robinson, E. S. Rubin, M. W. Schlegel, T. R. Stephenson,
B. A. Sterling, J. C. Whiting, D. T. Wilckins, and F. S.
Winslow. K. P. Hurley and the Northern Wild Sheep and
Goat Council provided the list-serve to access the cumulative
knowledge of biologists associated with bighorn sheep. I also
thank M. S. Boyce and P. R. Krausman for initiating this
Special Feature of The Journal of Wildlife Management and for
their editorial acumen. L. G. Adams, J. L. Davis, V. Geist,
B. M. Jansen, S. M. Murphy, N. T. Quintana, C. Q. Ruhl,
and 2 anonymous reviewers provided their time and
comments on previous versions of the manuscript. I
acknowledge NMDGF for the dedication to recovering
desert bighorn sheep.
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Supplementary resource (1)

... First, predation on bighorn sheep lambs can have a dramatic impact on survival rates (Berger 1991, Rominger et al. 2004, Festa-Bianchet et al. 2006, Brewer et al. 2014) and be critical to consider when evaluating potential sources of variation in population dynamics. Although the larger region has seen the recovery of populations of multiple predator species during our study period, mountain lions (Puma concolor) are implicated as the primary predator affecting bighorn sheep population dynamics (Rominger 2018). However, there is no direct measure of predation pressure from mountain lions or an index of it (e.g., mountain lion abundances) for a region the size of our study area and over the timespan of the data collection. ...
... In contrast to results for other sympatric ungulates where correlates of offspring recruitment and survival have been welldocumented to include intrinsic factors such as body mass and extrinsic factors such as predation and environmental factors (Singer et al. 1997, Côté and Festa-Bianchet 2001, Garrott et al. 2003, 2008b, White et al. 2010, Creel et al. 2011, Lukacs et al. 2018, fewer assessments of similar drivers have been done for bighorn sheep lambs (Douglas and Leslie 1986, Hass 1989, Portier et al. 1998, Douglas 2001, Brewer et al. 2014. Results of those assessments suggest that bighorn sheep lamb survival can be affected by a similarly diverse set of processes and that lambs may be quite susceptible to predation from mountain lions (Rominger 2018), and our results are broadly consistent with those findings, with the notable exception that we found no relationship between lamb survival and our proxy for the risk of predation from mountain lions. We attribute this result to the difficulties inherent in developing a suitable proxy for predation in the absence of relationship between lamb survival and growing season conditions (as measured by spring and summer precipitation and primary production) can vary among populations and suggest that the nature of the relationship might differ depending on the range of conditions to which a population is exposed, a possibility that will require further work to elucidate. ...
Article
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Understanding how variation in vital rates interact to shape the trajectories of populations has long been understood to be a critical component of informed management and restoration efforts. However, an expanding body of work suggests that the expectations for population dynamics of ungulates may not be applicable to small, declining, or threatened populations. Populations of bighorn sheep (Ovis canadensis) suffered declines at the turn of the 20th century, and restoration efforts have been mixed such that many populations remain small and isolated. Here, we utilized survey data collected from 1983 to 2018 from 17 populations of bighorn sheep in Montana and Wyoming to estimate the parameters of a stage‐specific population model that we used to (1) characterize the spatial and temporal variation in key vital rates including whether populations were stable, increasing, or declining; (2) estimate the contributions of vital rates to variation in population growth rates; and (3) evaluate potential sources of variation in lamb survival. We found substantial variation in all vital rates both among years and populations, strong evidence for an overall decline in nine of the 17 populations, and clear evidence for multiple combinations of vital rates that resulted in positive population trajectories. The contribution of ewe survival and lamb survival to the total variation in population growth rates varied among populations; however, declines in ewe survival dominated transitions of population trajectories from stable or increasing to declining, whereas reversals of declining population trajectories were dominated by improved lamb survival. We found strong evidence for a diverse set of associations between lamb survival and environmental covariates related to growing season and winter severity. The estimated relationships predict that environmental drivers can cause important changes in lamb survival and provide suggestive evidence that the presence of Mycoplasma ovipneumoniae is not sufficient to prevent population growth. Although our work demonstrates that the trajectories of these populations of bighorn sheep are driven by a variety of processes, the diversity of relationships between vital rates and population growth rates also suggests that there are multiple pathways to manage for population recovery.
... Jaguars directly compete with cougars in northern Mexico (Rosas-Rosas, Bender, & Valdez, 2008), though not to the extent of competitive exclusion (Gutiérrez-González & López-González, 2017). If jaguars kleptoparasitize cougars, then cougars may kill more prey to replace lost food and switch to other prey items (e.g., Krofel, Kos, & Jerina, 2012;Rominger, 2018). Jaguars might also compete with non-felid predators, such as black bears (Ursus americanus; Fourvel et al., 2014;Tallian et al., 2017). ...
... Both those jaguars escaped alive, with no harm to the hunters, though some chase hounds were injured. As with deer, jaguars may influence the behavior of cougars, wolves, and smaller predators, with cascading consequences for other hunted species, such as turkeys, javelinas, and bighorn sheep (Ovis canadensis; e.g., Rominger, 2018). Jaguars might take young Rocky Mountain elk, another reintroduced species (Witmer, 1990). ...
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Reintroduction—defined here as the return of a species to a part of its range where it has been extirpated—is a critical pathway to conservation in the 21st century. As late as the 1960s, jaguars (Panthera onca) inhabited an expansive region in the central mountain ranges of Arizona and New Mexico in the United States, a habitat unique in all of jaguar range. Here, we make the case for reintroduction, building a rhetorical bridge between conservation science and practice. First, we present a rationale rooted in the philosophy of wildlife conservation. Second, we show that the species once occupied this territory and was extirpated by human actions that should no longer pose a threat. Third, we demonstrate that the proposed recovery area provides suitable ecological conditions. Fourth, we discuss how return of the species could be a net benefit to people, explicitly recognizing a diversity of values and concerns. Fifth, we show that reintroduction is practical and feasible over a realistic time horizon. Returning the jaguar to this area will enhance the recovery of an endangered species in the United States, further its range‐wide conservation, and restore an essential part of North America's cultural and natural heritage.
... For instance, populations of grazing mammals lacking predation have higher growth rates with less variability 33 . Therefore, when populations experience predation, predator control can improve population sizes of Caprinae by raising the survival of adult females and recruitment 12,34,35 . Survival of adult females can increase 5-12% with predator control, and survival with predation is often twice as variable as populations without predation 12 . ...
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Stable or growing populations may go extinct when their sizes cannot withstand large swings in temporal variation and stochastic forces. Hence, the minimum abundance threshold defining when populations can persist without human intervention forms a key conservation parameter. We identify this threshold for many populations of Caprinae, typically threatened species lacking demographic data. Doing so helps triage conservation and management actions for threatened or harvested populations. Methodologically, we used population projection matrices and simulations, with starting abundance, recruitment, and adult female survival predicting future abundance, growth rate (λ), and population trend. We incorporated mean demographic rates representative of Caprinae populations and corresponding variances from desert bighorn sheep (Ovis canadensis nelsoni), as a proxy for Caprinae sharing similar life histories. We found a population’s minimum abundance resulting in < 0.01 chance of quasi-extinction (QE; population <5 adult females) in 10 years and < 0.10 QE in 30 years as 50 adult females, or 70 were translocation (removals) pursued. Discovering the threshold required 3 demographic parameters. We show, however, that monitoring populations’ relationships to this threshold requires only abundance and recruitment data. This applied approach avoids the logistical and cost hurdles in measuring female survival, making assays of population persistence more practical.
... In that case, pigs were eradicated, golden eagles were relocated to the mainland, and marine-dependent bald eagles (Haliaeetus leucocephalus) were introduced to fill the niche formally occupied by the golden eagle. The "apparent competition" (Holt, 1977(Holt, , 1984 between foxes and pigs is in fact a predator-prey dynamic that is well documented in other systems, often with implications for conservation and management (DeCesare et al., 2010;Rominger, 2018). In such cases, the most obvious solution is to remove the primary prey species or the predator to the advantage of the endangered species. ...
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Lethal population control has a history of application to wildlife management and conservation. There is debate about the efficacy of the practice, but more controversial is the ethical justification and methods of killing one species in favor of another. This is the situation facing the conservation of woodland caribou (Rangifer tarandus caribou) in Canada. Across multiple jurisdictions, large numbers of wolves (Canis lupus), and to a lesser extent bears (Ursus americanus) and coyotes (C. latrans), are killed through trapping, poisoning or aerial shooting to halt or reverse continued declines of woodland caribou. While there is evidence to support the effectiveness of predator management as a stop‐gap solution, questions remain about the extent to which this activity can make a meaningful contribution to long‐term recovery. Also, there are myriad ethical objections to the lethal removal of predators, even if that activity is in the name of conservation. Debates about predator management, just one of numerous invasive actions for maintaining caribou, are made even more complex by the conflation of ethics and efficacy. Ultimately, long‐term solutions for the recovery of caribou require governments to stop delaying difficult decisions that address the real causes of population decline, habitat change.
... Despite some evidence of localized range recolonizations (Thompson and Jenks, 2010;LaRue et al., 2012;Mazzolli, 2012), pumas remain absent from most of midwestern and eastern North America and populations are likely declining in parts of South America (Nielsen et al., 2015). The primary causes of puma population declines and range reductions have been habitat destruction from human activities and human-caused mortality, including but not limited to hunting and trapping, retaliatory and illegal killings, government-directed killings, vehicle collisions, and poisonings (Quigley and Hornocker, 2010;Nielsen et al., 2015;Rominger, 2018;Logan, 2019;van de Kerk et al., 2019;Logan and Runge, 2021). ...
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Range-wide status assessments of wildlife are critical to effective species conservation and management. Reliability of these assessments is contingent on having accurate and precise demographic estimates for local populations, but for large carnivores, such estimates are often biased, imprecise, or unavailable. Despite being the most widely distributed large carnivore in the Americas, little is known about the range-wide population status of the puma (Puma concolor). Population density is frequently the primary demographic metric used in puma conservation and management decision-making and policy; therefore, we conducted a comprehensive, range-wide, systematic review of capture-recapture and mark-resight model-based puma density estimates published through 2021 and used Bayesian multilevel models to investigate potential sources of bias and variation. Model-based puma density estimates have been produced in just 8 countries (42% of countries with puma populations) for study areas that cumulatively represent <1% of extant puma range. Most estimates applied to small study areas (median = 265 km2), protected areas (70%), and represented high quality habitats, such as forests and mixed savannas (89%). Nonspatial models likely overestimated puma density by an average of 63%, and inclusion of dependent individuals (e.g., kittens) in detection histories resulted in density estimates that were, on average, ~33% higher than estimates for independent individuals only, highlighting the need for standardization. After correcting for those potential biases, range-wide mean and median densities were 1.81 and 1.63 independent pumas/100 km2 (95% CI = 1.62, 2.02), respectively, with a 95th percentile of 3.64 independent pumas/100 km2. Although puma densities did not differ between North and South America, between protected and unprotected areas, or among human disturbance severities, support existed for puma density varying at the landscape-scale as a function of multiple geographical, environmental, and climatic characteristics (e.g., biome, precipitation, vegetation quality, and elevation). However, most puma density estimates were imprecise (90% had CV > 0.20) and likely positively biased, primarily because of small study area sizes and issues associated with some sampling and analytical methods; for example, we observed a potential 31–33% overestimation of puma density when spatially unstructured genetic sampling was used. Consequently, the quality of many existing model-based puma density estimates may be inadequate for reliable conservation or management decision-making, and the current number and geographical extent of puma density estimates are likely insufficient to inform useful continental or range-wide status assessments for the species.
... We also observed pumas visiting and entering the same mine. We were surprised that bighorn sheep would enter a mine that one of their predators also entered (Rominger 2017), but the benefits of accessing minerals might overcome the dangers of entering a mine, much like chimpanzees (Pan troglodytes) that enter caves in Senegal despite the presence of predators that enter the same caves (Boyer Ontl and Pruetz 2020). ...
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Abandoned mines provide habitat for bats, but their importance to other wildlife is less understood. This descriptive study was designed to answer the following questions with an emphasis on carnivores: are wildlife species other than bats visiting abandoned mines, is wildlife entering abandoned mines, does wildlife visitation at abandoned mines differ seasonally, and does wildlife visitation differ at individual mines? To address these questions, we monitored 50 abandoned mines using remote cameras in the northern Sangre de Cristo Mountains, Colorado, USA, for 25,201 camera days from May 2017 to August 2020. We monitored mines in 2 phases. During phase 1 (May 2017–May 2019), we monitored 30 randomly selected mines to gather baseline data on carnivore visitation and to model carnivore visitation. During phase 2 (May 2019–August 2020), we monitored 27 mines to test the visitation model and to determine if carnivores visited multiple mines as they traveled across the landscape. We observed >48 species of vertebrates at mines, including 11 of 14 carnivore species known to occur in the Sangre de Cristo Mountains. Carnivores ranged in size from ringtails (Bassariscus astutus) to American black bears (Ursus americanus). Pumas (Puma concolor) visited mines most frequently and we observed pairs of adult pumas entering mines, presumably during courtship and mating.We also observed American black bears, pumas, and common gray foxes (Urocyon cinereoargenteus) visiting and entering mines with young. Carnivores visited mines at low levels throughout the year and visitation differed by season, temperature, and carnivore species, size, and family. Our most parsimonious generalized linear models identified mine elevation, entrance (portal) size, land cover type, tree cover, and aspect as significant predictors of visitation. Our top models explained ≥78% of the variation in carnivore visits and indicated that carnivores in the Sangre de Cristo Mountains were most likely to visit small horizontal mines at lower elevations in dense piñon (Pinus edulis)—juniper (Juniperus sp.) woodlands. We encourage resource managers to monitor abandoned mines for ≥1 year prior to closing or gating mines to understand which wildlife species might be affected by closures.
... Pumas (Puma concolor) are an elusive, sparsely occurring, and uniformly pelaged species for which population monitoring has proven challenging. Yet, due to the species' huge distribution, ecological role as a top-down regulator (Ripple & Beschta, 2006;Ripple et al., 2014;Rominger, 2018), and societal role as an umbrella or flagship species (Beier, 2009), population estimates are often sought for regional management or broad conservation strategies. While CTs are highly effective at photocapturing pumas, and potentially a costeffective method for estimating population size, pumas' lack of conspicuous markings makes them a controversial subject for photo-ID (Alexander & Gese, 2018;Foster & Harmsen, 2012). ...
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Camera traps (CTs), used in conjunction with capture–mark–recapture analyses (CMR; photo-CMR), are a valuable tool for estimating abundances of rare and elusive wildlife. However, a critical requirement of photo-CMR is that individuals are identifiable in CT images (photo-ID). Thus, photo-CMR is generally limited to species with conspicuous pelage patterns (e.g., stripes or spots) using lateral-view images from CTs stationed along travel paths. Pumas (Puma concolor) are an elusive species for which CTs are highly effective at collecting image data, but their suitability to photo-ID is controversial due to their lack of pelage markings. For a wide range of taxa, facial features are useful for photo-ID, but this method has generally been limited to images collected with traditional handheld cameras. Here, we evaluate the feasibility of using puma facial features for photo-ID in a CT framework. We consider two issues: (1) the ability to capture puma facial images using CTs, and (2) whether facial images improve human ability to photo-ID pumas. We tested a novel CT accessory that used light and sound to attract the attention of pumas, thereby collecting face images for use in photo-ID. Face captures rates increased at CTs that included the accessory (n = 208, χ² = 43.23, p ≤ .001). To evaluate if puma faces improve photo-ID, we measured the inter-rater agreement of 5 independent assessments of photo-ID for 16 of our puma face capture events. Agreement was moderate to good (Fleiss’ kappa = 0.54, 95% CI = 0.48–0.60), and was 92.90% greater than a previously published kappa using conventional CT methods. This study is the first time that such a technique has been used for photo-ID, and we believe a promising demonstration of how photo-ID may be feasible for an elusive but unmarked species.
... This strategy may be a result of co-evolution with coursing predators (Festa-Bianchet 1991) and might not be as effective against ambush predators such as mountain lions. In this sense, it has been hypothesized that the evolutionary response to coursing predators has resulted in an ecological trap when mountain lions become the dominant predator (Rominger 2017). ...
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Bighorn sheep (Ovis canadensis) evolved for thousands of years in the presence of numerous predators, including mountain lions (Puma concolor). Bighorn sheep have presumably developed predator avoidance strategies; however, the effectiveness of these strategies in reducing risk of mountain lion predation is not well understood. These strategies are of increasing interest because mountain lion predation on bighorn sheep has been identified as a leading cause of mortality in some sheep populations. Therefore, we investigated how mountain lions affect both bighorn sheep habitat selection and risk of mortality in Arizona, USA. We used 2 approaches to investigate the predator‐prey relationship between mountain lions and bighorn sheep. We fit 103 bighorn sheep (81 females and 22 males) with global positioning system radio‐collars in 2 Arizona populations from 2013 to 2017, and used a negative binomial resource selection probability function to evaluate whether bighorn sheep selected for habitat features in accordance with presumed predator avoidance strategies, including terrain ruggedness, slope, topographic position, and horizontal obstruction, in 2 seasons (winter and summer). We then estimated how habitat features such as terrain ruggedness, slope, horizontal obstruction, and group size, influence the risk of mortality due to mountain lion predation using an Andersen‐Gill proportional hazards model. Generally, both sexes selected areas with lower horizontal obstruction and intermediate ruggedness and slope, but selection patterns differed between seasons and sexes. The use of more rugged areas and steeper slopes decreased the risk of mortality due to mountain lion predation, consistent with presumed predator avoidance strategies. Increased group size decreased risk of bighorn sheep mortality due to mountain lion predation but this effect became marginal at approximately 10 individuals/group. We did not identify a relationship between horizontal obstruction and bighorn sheep mortality risk. Our findings can be used in habitat and population management decisions such as the prioritization of habitat restoration sites or selection of translocation sites. In addition, we suggest that augmentation of low‐density bighorn sheep populations may reduce mountain lion predation risk by increasing group size, and that releasing large groups of bighorn sheep in population augmentation and reintroduction efforts may help to reduce mountain lion predation. Bighorn sheep selected for areas with decreased horizontal obstruction and areas of intermediate slope and ruggedness. Ruggedness, steep slopes, and increased bighorn sheep group size decrease the risk of bighorn sheep mortality due to mountain lion predation. We suggest that habitat manipulations, such as prescribed fire, and translocating larger groups of bighorn sheep may increase the amount of available bighorn sheep habitat and decrease the risk of bighorn sheep mortality due to mountain lion predation, respectively.
... Lion predation is a common cause of mortality in ungulates and often occurs at relatively low and constant rates over time, with minimal impact on prey population dynamics (Laundré et al. 2006;Forrester and Wittmer 2013), but in small populations of bighorn sheep, impacts can be pronounced (reviewed in Rominger 2018). Irruptions in lion predation rates, particularly on small and/or endangered prey populations, can substantially exceed long-term averages in an apparently stochastic manner (Festa-Bianchet 2006) and may be the result of individual "specialist" predators whose dietary selection differs from the population mean (Ross et al. 1997;Logan and Sweanor 2001;Festa-Bianchet 2006;Elbroch and Wittmer 2013;Wittmer et al. 2014). ...
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Translocation of animals into formerly occupied habitat is a key element of the recovery plan for Sierra Nevada bighorn sheep (Ovis canadensis sierrae), which are state (California) and federally listed as endangered. However, implementing Sierra bighorn translocations is a significant conservation challenge because of the small size of the extant population and the limited number of herds available to donate transloca-tion stock. One such herd, the Mt. Langley herd, recently became unusable as a translocation source following a substantial population decline. At the time of listing in 1999, predation by mountain lions (Puma concolor; hereafter lion) was considered a primary threat to Sierra bighorn, and since then lion predation may have continued to limit the ability of source herds to provide translocation stock. We evaluated the relationship between lion predation and ewe survival rates within three source herds of the Southern Recovery Unit, compared lion abundance and ewe survival among years of varying predation levels, provided a range of estimated times for the Mt. Langley herd to recover to its former status as a translocation source, and determined if the rates lions have been removed to mitigate Sierra bighorn predation exceeded sustainable harvest guidelines. We found compelling evidence that lion predation has impeded the recovery of Sierra bighorn by reducing survival rates of adult ewes (and consequently, population growth) and by preying upon individuals that could have otherwise been translocated. Ewe survival was poor during years of extreme predation but even during years of typical predation, survival rates were below a level needed to ensure population growth, indicating that years with little or no lion predation may be necessary for the population to grow and meet recovery goals. Because the intensity of predation was related to lion abundance, monitoring lion populations could provide managers with advance warning of periods of extreme predation. We found that fol-lowing a period of particularly extreme predation, the Mt. Langley herd decreased in abundance far below the threshold needed to be considered a source of translocation stock, resulting in the loss of approximately 25% of the recovery program’s capacity for translocations. It is unclear how many years it will take for this herd to recover, but management ac-tions to reduce lion predation are likely needed for this herd to grow to a size that can afford to donate individuals to translocation efforts in the near future, even when optimistic growth rates are assumed. We found that lion removal may also be needed to prevent predation from leading to Sierra bighorn population decline. Lion removal rates that have been implemented thus far are well below what would be needed to reduce the abundance the eastern Sierra lion population itself. We recommend continued monitoring of Sierra bighorn and sympatric lions and note that lion removal may be required to facilitate bighorn recovery for the foreseeable future.
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To improve lifetime reproductive success, maternal ungulates should pursue behavioral strategies that reduce risk of offspring mortality. Predation is a leading cause of neonatal mortality; thus, maternal ungulates should select habitat that reduces risk of predation on vulnerable neonates. We examined selection of habitat across subpopulations of federally endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae) within Sierra Nevada, California, USA, 2008–2018. Our objectives were to understand how maternal Sierra Nevada bighorn minimize risk of predation through selection of habitat and to quantify current and future potential neonatal habitat across the Sierra Nevada. Mountain lions (Puma concolor) are the predominant predators of adult Sierra Nevada bighorn; thus, we hypothesized females would select habitat that minimized risk of predation from mountain lions. We developed a used‐available resource selection function to quantify patterns of habitat selection and produced predictive maps identifying highly selected lambing habitat across the Sierra Nevada. Our top model demonstrated females selected habitat where the relative probability of encountering mountain lions was low and near escape terrain. Selection for vegetation type was dependent on risk of encounter with mountain lions; when risk of encounter was low, females selected shrub cover. This suggests that when risk of encountering mountain lions was low, females may have selected areas with dense shrubs to reduce risk of being detected by other predators such as coyotes (Canis latrans) and golden eagles (Aquila chrysaetos). As risk of encountering mountain lions increased, females avoided all vegetation types other than barren, suggesting that despite increased risk of encounter, females may have been able to mitigate overall mortality risk by selecting habitat where approaching mountain lions could be detected and avoided. Our predictive models and resulting maps demonstrate differences in prevalence and connectivity of highly selected lambing habitat across subpopulations, which may explain differences in lamb recruitment and adequacy of lambing habitat observed among subpopulations. Recolonization into historical ranges and increasing connectivity between Sierra Nevada bighorn subpopulations is an important conservation need for species recovery and long‐term viability of fragmented subpopulations. We determined that maternal Sierra Nevada Bighorn females selected for habitat that minimized risk of predation from mountain lions. Our predictive maps demonstrated that abundance of high‐quality neonatal habitat differs across subpopulations, and will allow managers to prioritize potential translocation sites likely to promote reproductive success.
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Habitat choice is an evolutionary product of animals experiencing increased fitness when preferentially occupying high-quality habitat. However, an ecological trap (ET) can occur when an animal is presented with novel conditions and the animal's assessment of habitat quality is poorly matched to its resulting fitness. We tested for an ET for grizzly (brown) bears using demographic and movement data collected in an area with rich food resources and concentrated human settlement. We derived measures of habitat attractiveness from occurrence models of bear food resources and estimated demographic parameters using DNA mark-recapture information collected over 8 years (2006-2013). We then paired this information with grizzly bear mortality records to investigate kill and movement rates. Our results demonstrate that a valley high in both berry resources and human density was more attractive than surrounding areas, and bears occupying this region faced 17% lower apparent survival. Despite lower fitness, we detected a net flow of bears into the ET, which contributed to a study-wide population decline. This work highlights the presence and pervasiveness of an ET for an apex omnivore that lacks the evolutionary cues, under human-induced rapid ecological change, to assess trade-offs between food resources and human-caused mortality, which results in maladaptive habitat selection.
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Desert mule deer (Odocoileus hemionus eremicus) densities in central Arizona are below historic levels, likely due to neonatal mortality influencing desert mule deer population dynamics. However, no direct assessments have been made into causes and timing of neonatal mortalities in central Arizona. The objectives of our study were to determine the causes and timing of mortalities of desert mule deer fawns, estimate the annual survival rate of adult females and fawns, and quantify predator effects on fawn survival. In 2007 and 2008 we captured 52 adult female desert mule deer and equipped pregnant females with vaginal implant transmitters to aid in capturing fawns. We performed survival analyses using Program MARK and compared competing models with Akaike's information criterion. We captured 44 desert mule deer fawns; summer survival was 0.432 (95% CI = 0.292–0.584) and annual fawn survival was 0.071 (95% CI = 0.013–0.303). Predation accounted for 64% of fawn mortality. Probability of fawn survival was lowest in the first 2 weeks postparturition. Most (50 of 51) adult females of breeding age were pregnant and adult female survival was 0.858 (95% CI = 0.766–0.961). High predation rates and timing of predation on mule deer fawns were important factors influencing deer densities in central Arizona.
Book
Once plentiful in the mountains of southern Arizona, by the 1990s desert bighorn sheep were wiped out in the Pusch Ridge Wilderness of the Santa Catalina Mountains as a result of habitat loss and alteration. This book uses their history and population decline as a case study in human alteration of wildlife habitat. When human encroachment had driven the herd to extinction, wildlife managers launched a major and controversial effort to reestablish this population. For more than forty years Paul R. Krausman directed studies of the Pusch Wilderness population of these iconic animals, located in the mountainous outskirts of Tucson. The story he tells here reveals the complex relationships between politics and biology in wildlife conservation. His account of the evolution of wildlife conservation practices includes discussions of techniques and of human attitudes toward predators, fire, and their management. © 2017 by the University of New Mexico Press. All rights reserved.
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The authors monitored survival of 60 woodland caribou Rangifer tarandus translocated from British Columbia to the Selkirk Mountains of N Idaho between March 1987 and February 1992, to assist in recovery of the endangered Selkirk population. For all translocated caribou combined, estimated annual survival rates ranged from 0.65-0.94 and were consistent with declining, established populations. The greatest proportion (53%) of deaths was in summer. Mountain lions Felis concolor caused most confirmed predator kills. Seasonal patterns of mortality was consistent with established populations where predation was identified as a significant factor. -from Authors
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Fitness of female ungulates is determined by neonate survival and lifetime reproductive success. Therefore, adult female ungulates should adopt behaviors and habitat selection patterns that enhance survival of neonates during parturition and lactation. Parturition site location may play an important role in neonatal mortality of desert bighorn sheep (Ovis canadensis mexicana) when lambs are especially vulnerable to predation, but parturition sites are rarely documented for this species. Our objectives were to assess environmental characteristics at desert bighorn parturition, lamb nursery, and predation sites and to assess differences in habitat characteristics between parturition sites and nursery group sites, and predation sites and nursery group sites. We used vaginal implant transmitters (VITs) to identify parturition sites and capture neonates. We then compared elevation, slope, terrain ruggedness, and visibility at parturition, nursery, and lamb predation sites with paired random sites and compared characteristics of parturition sites and lamb predation sites to those of nursery sites. When compared to random sites, odds of a site being a parturition site were highest at intermediate slopes and decreased with increasing female visibility. Odds of a site being a predation site increased with decreasing visibility. When compared to nursery group sites, odds of a site being a parturition site had a quadratic relationship with elevation and slope, with odds being highest at intermediate elevations and intermediate slopes. When we compared predation sites to nursery sites, odds of a site being a predation were highest at low elevation areas with high visibility and high elevation areas with low visibility likely because of differences in hunting strategies of coyote (Canis latrans) and puma (Puma concolor). Parturition sites were lower in elevation and slope than nursery sites. Understanding selection of parturition sites by adult females and how habitat characteristics at these sites differ from those at predation and nursery sites can provide insight into strategies employed by female desert bighorn sheep and other species during and after parturition to promote neonate survival.