COLORADO BIGHORN SHEEP MANAGEMENT PLAN 2009−2019

stock (Singer et al. 2000). Selective harvest of large
rams also may cause drift in genes that influence horn
size (Fitzsimmons et al. 1995).
Because of these concerns, many bighorn
translocations have been done to supplement existing
herds for the purpose of increasing genetic diversity even
in the absence of conclusive information on negative
effects of low genetic diversity. Unfortunately, the
inherent risks of disease transmission associated with
supplemental translocations of bighorn sheep have been
demonstrated in Colorado, and those consequences
appear far more severe than the ostensible effects of
diminished genetic diversity. Disease screening to
identify herds with similar exposure to pathogens is
necessary to lessen the likelihood of disease outbreaks
in the recipient or translocated sheep; however,
additional data are needed to improve the effectiveness
and interpretation of existing approaches.
As a means of limiting further compromise in the
genetic integrity of Colorado’s bighorn populations,
it may be useful to estimate genetic variation within
and among primary core populations and develop
strategies for maintaining maximum genetic diversity
to the extent feasible based on the genetic distance
between populations (i.e., populations with the greatest
genetic distance should receive management priority).
However, any planning done to achieve and maintain
genetic diversity in primary core populations also should
consider the potential for introducing or spreading
pathogens among bighorn herds and populations
with disparate exposure histories. Comparing genetic
variation of bighorn sheep may be accomplished
using loci from nuclear DNA (e.g., allozymes and
microsatellites) or mitochondrial DNA (Luikart and
Allendorf 1996, Fitzsimmons et al. 1997, Gutierrez-
Espeleta et al. 2000).
Environmental Stress
Bighorn sheep often appear to habituate fairly well to
human activity. However, under some circumstances
it is possible that bighorns may be adversely affected
by chronic exposure to stressors as has been reported
for a variety of other mammalian species. Stressinduced
responses might increase susceptibility to
diseases such as pasteurellosis in individual bighorns
and thus could contribute the onset of epidemics in
some situations (Spraker et al. 1984, Kraabel and
Miller 1997).
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Interspecies Competition
Competitive interaction between bighorn sheep and
other wild ungulates can result from dietary overlap
and from displacement from preferred habitat. Bighorn
sheep, mountain goats, mule deer (O. hemionus), and elk
all show some degree of dietary overlap that can vary
by location and season. Mountain goats and bighorns
have similar habitat requirements and can be direct
competitors in some cases. Based on observations
of interactions between mountain goats and Rocky
Mountain bighorn sheep, mountain goats are often the
more aggressive and dominant species and appear to
be capable of displacing bighorns (e.g., Carpenter and
Ramey 2007. Also see photos pp.74.) The DOW
has therefore managed mountain goat populations and
distribution to limit the expansion of mountain goats into
areas occupied by Rocky Mountain bighorn sheep.
Competition with mule deer can potentially have
negative impacts on bighorns primarily because mule
deer are much more common than sheep. However,
except during periods of extreme food shortage, there
is little evidence that competition with mule deer is a
significant limiting factor for bighorn sheep. It is more
likely that competition with elk would have a greater
negative effect because elk are much larger, they are
capable of having broader dietary overlap with bighorn
sheep, and large herds of elk can gather in alpine areas
traditionally used by bighorns.
Exotic sheep species such as mouflon (Ovis musimon)
and aoudads (or Barbary sheep; Ammotragus lervia) can
potentially compete with bighorn sheep and introduce
infectious diseases; mouflon also can readily interbreed
with bighorns. Consequently, all exotic, wild species
of Caprinae are prohibited in Colorado by Wildlife
Commission regulations. Escapes of exotic sheep and
goats have occurred in the past in the Battlement Mesa
area, in the Black Canyon of the Gunnison River, and
near Pikes Peak.
Harvest & Translocation Off-take
Harvest rates in Colorado are low enough in most herds
(e.g.,