Index of Species Information
WILDLIFE SPECIES: Ovis canadensis
WILDLIFE SPECIES: Ovis canadensis
AUTHORSHIP AND CITATION :
Tesky, Julie L. 1993. Ovis canadensis. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/ .
COMMON NAMES :
The currently accepted scientific name for the bighorn sheep is Ovis
canadensis Shaw [6,13]. Subspecies are listed below .
Ovis canadensis subsp. canadensis (Rocky mountain bighorn sheep)
Ovis canadensis subsp. auduboni Merriam (Audubon's bighorn sheep)
Ovis canadensis subsp. californiana Douglas (California bighorn sheep)
Ovis canadensis subsp. cremnobates Elliot (Peninsular desert bighorn sheep)
Ovis canadensis subsp. mexicana Merriam (Mexican desert bighorn sheep)
Ovis canadensis subsp. nelsoni Merriam (Nelson's Peninsular bighorn sheep)
Ovis canadensis subsp. sierrae (Sierra Nevada bighorn sheep)
Ovis canadensis subsp. weemsi Goldman (Weem's desert bighorn sheep)
FEDERAL LEGAL STATUS :
Nelson's Peninsular and Sierra Nevada bighorn sheep are listed as endangered .
OTHER STATUS :
Information on state- and province-level protection status of animals in the
United States and Canada is available at NatureServe, although recent changes
in status may not be included.
WILDLIFE DISTRIBUTION AND OCCURRENCE
WILDLIFE SPECIES: Ovis canadensis
GENERAL DISTRIBUTION :
The former range of the bighorn sheep extended from the Northern Rocky
Mountains of Canada south to the mainland of Mexico and Baja California
. It is now found in relatively isolated pockets in the Coast and
Cascade ranges and the Sierra Nevada, and in the Rocky Mountains south
of the Peace River to Mexico .
FRES21 Ponderosa pine
FRES26 Lodgepole pine
FRES30 Desert shrub
FRES32 Texas savanna
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES40 Desert grasslands
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
16 Upper Missouri Basin and Broken Lands
KUCHLER PLANT ASSOCIATIONS :
K003 Silver fir - Douglas-fir forest
K004 Fir - hemlock forest
K005 Mixed conifer forest
K010 Ponderosa shrub forest
K011 Western pondersoa forest
K012 Douglas-fir forest
K015 Western spruce - fir forest
K016 Eastern ponderosa forest
K018 Pine - Douglas-fir forest
K019 Arizona pine forest
K020 Spruce - fir - Douglas-fir forest
K021 Southwestern spruce - fir forest
K022 Great Basin pine forest
K024 Juniper steppe woodland
K023 Juniper - pinyon woodland
K028 Mosaic of K002 and K026
K029 California mixed evergreen forest
K031 Oak - juniper woodlands
K032 Transition between K031 and K037
K035 Coastal sagebrush
K037 Mountain-mahogany - oak scrub
K038 Great Basin sagebrush
K040 Saltbush - greasewood
K042 Creosotebush - bursage
K047 Fescue - oatgrass
K050 Fescue - wheatgrass
K051 Wheatgrass - bluegrass
K053 Grama - galleta steppe
K054 Grama - tobosa prairie
K057 Galleta - three-awn shrubsteppe
K058 Grama - tobosa shrubsteppe
K059 Trans-Pecos shrub savanna
K052 Alpine meadows and barren
K063 Foothills prairie
K064 Grama - needlegrass - wheatgrass
K065 Grama - buffalograss
K066 Wheatgrass - needlegrass
K067 Wheatgrass - bluestem - needlegrass
K068 Wheatgrass - grama - buffalograss
K069 Bluestem - grama prairie
K070 Sandsage - bluestem prairie
K074 Bluestem prairie
SAF COVER TYPES :
204 Black spruce
205 Mountain hemlock
206 Engelmann spruce - subalpine fir
208 Whitebark pine
210 Interior Douglas-fir
218 Lodgepole pine
220 Rocky Mountain juniper
230 Douglas-fir - western hemlock
237 Interior ponderosa pine
238 Western juniper
239 Pinyon - juniper
SRM (RANGELAND) COVER TYPES :
PLANT COMMUNITIES :
Bighorn sheep occupy a variety of plant communities ranging from alpine
meadows, woodlands, mixed-grass prairie, shrub-bunchgrass, and dry
pinyon-juniper (Pinus-Juniperus spp.) [2,7,14,25,27]. They avoid dense
Summer ranges of bighorn sheep in southeastern Oregon vary from
subalpine meadows or grasslands to sagebrush (Artemisia spp.)/grasslands
or shrublands. Winter ranges are usually shrub/grasslands and
shrublands. Communities dominated by trees or tall shrubs such as aspen
(Populus spp.), cottonwood (Populus spp.), fir (Abies spp.), pine,
juniper, mountain-mahogany (Cercocarpus spp.), squaw apple (Peraphyllum
ramosissimum), and cherry (Prunus spp.) may occur throughout both summer
and winter ranges .
On two bighorn sheep winter ranges in the upper Yellowstone River
Valley, vegetation types in which bighorns were observed included
bluebunch wheatgrass (Pseudoroegneria spicata), needle-and-thread (Stipa
comata), and Idaho fescue (Festuca idahoensis) grasslands; sagebrush
(primarily A. tridentata) and black greasewood (Sarcobatus vermiculatus)
shrublands; open Douglas-fir (Pseudotsuga menziesii) woodland; and the
vegetation mosaics associated with cliffs and draws . Bighorn sheep
range in Glacier National Park includes bunchgrass communities dominated
by bluebunch wheatgrass, Idaho fescue, rough fescue (F. scrabrella), and
Saskatoon serviceberry (Amelanchier alnifolia); and seral vegetation of
subalpine fir (Abies lasiocarpa) habitat types .
Other plant species common on bighorn sheep range include bitterbrush
(Purshia tridentata), mountain muhly (Muhlenbergia montana), russet
buffaloberry (Shepherdia canadensis), bearberry (Arctostaphylos
uva-ursi), blue grama (Bouteloua gracilis), rabbitbrush (Chrysothamnus
spp.), bluegrass (Poa spp.), buffalograss (Buchloe dactyloides), western
wheatgrass (Pascopyron smithii), and sedges (Carex spp.) [2,7,11,24,25].
BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Ovis canadensis
TIMING OF MAJOR LIFE HISTORY EVENTS :
Breeding season - Bighorn sheep are polygamous. Ewes are monesterous.
Rams of most subspecies rut in November and December. However, desert
bighorn sheep may rut for up to 9 months, with rutting reaching a peak
in August and September .
Age at sexual maturity - The age at which ewes attain sexual maturity is
quite variable and is dependent mainly on their physical condition .
Most bighorn sheep become mature at 2.5 years of age. Large-bodied rams
may reach sexual maturity within 18 months, but smaller rams may take as
long as 36 months. Very old ewes generally do not breed .
Gestation and lambing - The gestation period is 5.5 to 6 months. The
majority of ewes give birth to one lamb per year. Lambing of northern
bighorn sheep occurs between late April and late June, with most lambs
born before the end of May. Desert bighorn sheep ewes give birth
throughout the year; however, the peak is from January to April .
Development of lambs - Bighorn sheep lambs are precocious and within a
day or so climb almost as well as their mothers. Within 2 weeks lambs
can eat grass. They are weaned between 1 and 7 months. By their second
spring bighorn sheep are totally independent of their mother. Ewes
reach their adult weight by 4 to 5 years of age, while rams do not
achieve maximum weight until they are 6 or 7 years old .
Life span - Mortality is high for bighorn sheep 1 to 2 years of age,
drops to a relatively low rate for 2 to 8 years of age, then increases
to a maximum for those older than 8 to 9 years. Bighorn sheep that live
past 8 or 9 years may live to 15 to 17 years of age, but 10 to 12
years is more common .
Bighorn sheep are territorial. By 4 years of age, individuals have
established home ranges that are utilized throughout their life span .
PREFERRED HABITAT :
Bighorn sheep inhabit remote mountain and desert regions. They are
restricted to semiopen, precipitous terrain with rocky slopes, ridges,
and cliffs or rugged canyons [6,26]. Forage, water, and escape terrain
are the most important components of bighorn sheep habitat .
Winter range - Generally, bighorn sheep have two distinct, separate
summer and winter ranges . Most of the year is spent on the winter
range, where the elevation is typically below 10,826 feet (3,300 m).
The aspect is usually south or southwest. Rams often venture onto the
more open slopes, although rugged terrain is always nearby. Desert
bighorn sheep rarely stray far from the base of a mountain and usually
are found on eastern aspects, where they use dry gullies. During
severe weather, if snow becomes unusually deep or crusted, bighorn sheep
move to slightly higher elevations where wind and sunshine have cleared
the more exposed slopes and ridges .
Spring range - The spring range is generally characterized by the same
parameters as the winter range. However, bighorn sheep begin to respond
to local greenups along streambanks and valleys. Bighorn sheep use
areas around saltlicks heavily in the spring. Preferred lambing range
is in the most precipitous, inaccessible cliffs near forage, and
generally has a dry, southern exposure .
Summer range - In the summer, bighorn sheep are mostly found grazing on
grassland meadows and plateaus above timber. In early summer south and
southwestern exposures are most frequently utilized; however, in the
case of the desert bighorn sheep the eastern aspect is preferred. By
late summer the more northerly exposures are preferred . Snow
accumulation seems to be the principal factor that triggers bighorn
sheep to move from summer to winter ranges .
Water - Bighorn sheep obtain water from dew, streams, lakes, springs,
ponds, catchment tanks, troughs, guzzlers, and developed seeps or
springs . Alkaline water is not suitable. Bighorn sheep spend most
of their time within 1 mile (1.6 km) of water but have been located as
far as 2 miles (3.2 km) from water. Water sources more than 0.3 mile
(0.5 km) from escape terrain or surrounded by tall dense vegetation are
avoided by bighorn sheep . Desert bighorn sheep primarily utilize
ephemeral water sources. They may drink every day if water is nearby,
but may go without water for up to 14 days in the dry season. Since
water is one of the major limiting factors of desert bighorn sheep,
management agencies have installed cisterns and other water developments
in critical areas .
COVER REQUIREMENTS :
Escape terrain is an important habitat requirement for bighorn sheep.
Cliffs, rock rims, rock outcroppings, and bluffs with sparse cover of
trees or shrubs typify escape habitat, which provides both thermal and
hiding cover. While bighorn sheep are not always found in precipitous
mountain areas, ewes and lambs rely on these areas for escape cover,
especially during the lambing period [6,26,27].
Visibility is another important habitat component for bighorn sheep. It
allows for predator detection, visual communication, and efficient
foraging . Bighorn sheep tend to forage in open areas with low
vegetation such as grasslands, shrublands, or mixes of these. They
avoid foraging on mild slopes with shrub or canopy cover in excess of 25
percent and shrubs 2 feet (60 cm) or higher. On steep slopes they have
been noted to travel through or bed in dense brush .
FOOD HABITS :
Bighorn sheep primarily graze grasses and forbs, but eat other
vegetation depending on availability . They prefer green forage and
move up- or downslope or to different aspects for more palatable forage.
Forage areas that provide a variety of aspects are preferable because
they provide green forage for longer periods .
Bighorn sheep eat sedges and a variety of grasses including bluegrasses
(Poa spp.), wheatgrasses, bromes, and fescues. Browse species include
sagebrush, willow (Salix spp.), rabbitbrush, curlleaf mountain-mahogany
(Cercocarpus ledifolius), winterfat (Kraschnennikovia lanata),
bitterbrush, and green ephedra (Ephedra spp.). Forbs include phlox
(Phlox spp.), cinquefoil (Potentilla spp.), twinflower (Linnaea
borealis), and clover (Trifolium spp.) [6,23].
Because of the dry climate, browse is the dominant food of the desert
bighorn sheep and includes desert holly (Atriplex hymenelytra),
honeysweet (Tidestromia oblongifolia), brittlebush or encelia (Encelia
spp.), hairy mountain-mahogany (C. breviforus), Wright silktassel
(Garrya wrightii), desert mallow (Sphaeralcea ambigua), Russian-thistle
(Salsola kali), false mesquite (Calliandra eriophylla), goatnut
(Simmondsia chinensis), white ratany (Krameria canescens), bursage
(Hyptis emoryi), mesquite (Prosopis glandulosa), catclaw (Acacia
greggii), ironwood (Olneya tesota), paloverde (Cercidium spp.),
pincushion (Mammillaria spp.), and saguaro (Carnegiea gigantea). Dry
grasses are eaten throughout the year and are an important food reserve,
especially near waterholes .
Golden eagles (Aquila chrysaetos) occasionally threaten bighorn sheep
lambs, but are rarely successful in taking one. Bighorn sheep are an
incidental food item in the diet of grizzly or black bears (Ursus
arctos, U. americanus) and wolverines (Gulo gulo), and are generally
eaten only as carrion. Wolves (Canis lupus), coyotes (C. latrans),
mountain lions (Felis concolor), and bobcats (Lynx rufus) are other
predators of bighorn sheep [6,26]. The number of bighorn sheep taken by
predators is usually of little consequence to healthy populations.
Predators are most effective when locations of escape terrain or water
limit sheep movement and allow predators to concentrate hunting efforts
Bighorn sheep are hunted by humans. Hunting has traditionally been for
rams only and is further restricted by a 3/4 or full horn curl policy.
In the last few years most states and provinces have adopted more
stringent horn curl regulations. While the overall trend has been for
more restrictive hunting seasons, in some cases local situations have
dictated either sex or 1/2 curl ram seasons .
MANAGEMENT CONSIDERATIONS :
Bighorn sheep are very susceptible to diseases. Incidence of lungworm
infestation approaches 100 percent in some herds, although the level of
individual infection varies depending upon sheep and domestic livestock
densities, range conditions, climate, season, and age. Desert bighorn
sheep appear to have lighter infestations, possibly due to climate or
low density. A significant correlation exists between the intensity of
the lungworm infestation and the amount of precipitation in the spring
of the previous year. In Washington state both wild and captive bighorn
sheep have been successfully treated with the experimental drug
albendazole. Further research is needed to determine the feasibility of
treating remote populations .
The future of bighorn sheep depends on the preservation and improvement
of critical native ranges. Bighorn sheep are poor competitors with
other wild and domestic ungulates, and their range is diminishing.
The effect of domestic livestock grazing on bighorn sheep is
controversial and depends on the proximity and population size of
competing species. Domestic livestock have been reported to have little
deleterious effect if they do not graze on critical bighorn sheep winter
ranges. Nevertheless, extensive competition by livestock, especially on
public lands, persists and is one of the reasons for the decline in
density of bighorn sheep populations . Elk (Cervus elaphus) and deer
(Odocoileus virginianus and O. hemionus) can also be serious competitors
with bighorn sheep on marginal habitat [6,18].
Human activities on bighorn sheep range are the most widespread threat
to bighorn sheep . These activies reduce the number of bighorn sheep
by decreasing habitat, causing bighorn sheep to reduce or terminate
their use of prime habitat, stop migration, or split from large herds
into smaller herds [4,26]. Human activities responsible for declines in
sheep use of an area include hiking and backpacking, snow skiing, water
skiing, fishing, motorbiking, four-wheel-drive vehicle use, construction
and use of roads, urban development, and recreational development. When
bighorn sheep are pushed from prime to marginal habitat, mortality
usually increases and productivity decreases. Some herds have adapted
to human activity .
FIRE EFFECTS AND USE
WILDLIFE SPECIES: Ovis canadensis
DIRECT FIRE EFFECTS ON ANIMALS :
Prescribed burning and its associated human activity in bighorn sheep
range may increase stress levels in a population. Herd condition should
be considered when planning time of fire . No information is
available regarding the direct effects of fire on bighorn sheep.
HABITAT RELATED FIRE EFFECTS :
Many bighorn sheep populations originally occurred in areas with
frequent fire intervals [19,24]. Bighorn sheep inhabiting the Salmon
River drainage of Idaho occupy a region where over 64 percent of their
habitat has burned since 1900 .
Fire exclusion for over 50 years has allowed plant succession to alter
many bighorn sheep habitats throughout North America [6,7]. Fire
exclusion, which has allowed conifers to establish on grasslands, has
decreased both the forage and security values on many bighorn sheep
Fire is an important factor in creating habitats that are heavily used
by bighorn sheep [6,27]. Periodic burning keeps seral grasslands from
becoming dominated by coniferous trees . In April 1987, a
prescribed fire was conducted on 235 acres (95 ha) of bighorn sheep
winter range in Custer State Park, South Dakota. Burning expanded
foraging habitat for bighorn sheep by curtailing encroachment of
pondersosa pine (Pinus ponderosa) onto mixed-grass prairie.
Burning may regenerate rangelands and enhance the production,
availability, and palatability of important bighorn sheep forage species
. Bighorn sheep heavily utilized burned winter range the following
two winters after a September 1974 fire on the East Fork of the Salmon
River, Idaho . Over 66 percent of the plants on this burned range
had been grazed by bighorn sheep. Utilization was consistently higher
on burned sites than on adjacent unburned sites for at least 4 years
after the fire .
Burning can increase visibility for bighorn sheep. Research has shown
that on burned sites bighorn sheep use areas more distant to escape
terrain than on adjacent unburned sites .
Fire can negatively affect bighorn sheep habitat when range condition is
poor and forage species cannot recover, when nonsprouting species that
provide important forage for bighorn sheep are eliminated, or when too
much area is burned and forage is inadequate until the next growing
season. Another potentially negative effect is when other species,
especially elk, are attracted to prescribed burns intended to benefit
bighorn sheep .
FIRE USE :
Prescribed fire can be useful tool in managing bighorn sheep habitat
. Prescribed burning has been widely used to increase the quantity
and nutritional quality of bighorn sheep forage throughout North America
Prescribed crown fires conducted in winter in mature conifer stands
adjacent to escape terrain may provide an inexpensive solution to
maintaining or establishing bighorn sheep winter range. In areas where
the available bighorn sheep range is large and provides alternative and
distant wintering sites, fires should be prescribed or located in areas
that would minimize the stress on sheep. Early spring fires,
particularly on south and southwest aspects, may provide more spring
forage than would otherwise be available for bighorn sheep .
Burning immature forests and scrublands adjacent to bighorn sheep winter
range could also provide migration corridors between winter and summer
Prescribed burning has been used to establish and maintain subalpine
bighorn sheep range in British Columbia. According to Bentz and Woodard
, burning provides an economical method of converting subalpine
forests, which are of low value to bighorn sheep, to earlier seral plant
communities. On the British Columbia range, bighorn sheep used burned
sites more than adjacent unburned sites.
Since both positive and negative effects can occur from burning bighorn
sheep range, a well-thought-out plan must be developed before fire is
considered for use on their range. Plans must consider the following:
1) condition of plants
2) plant response to burning
3) adjacent conifers (The possibility of creating more open range exists
if conifer stands or tall shrub fields occur next to currently used ranges.)
4) limiting factors (factors that may limit bighorn sheep populations
should be identified, and an evaluation made as to how burning will
effect these limiting factors)
5) lungworm (lungworm infections can possibly be altered by reducing
bighorn sheep concentrations; however, if burns are small and
concentrate bighorn sheep, results could be negative. If burns disperse
populations, the effects could be positive)
6) competition from other ungulates attracted to burns 
FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find Fire Regimes".
WILDLIFE SPECIES: Ovis canadensis
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