Yellowstone's Northern Range - Greater Yellowstone Science ...

THE NORTHERN RANGE
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not aware of a decline in big sagebrush anywhere
else on the mule deer winter range, and lacking any
other lines of evidence, we can speculate that the
sagebrush decline may be due to heavy, year-round
use by pronghorn. To further complicate this
question, the sagebrush decline seems to be
restricted to the Wyoming subspecies, and mostly
to high ground such as ridges, upland slopes, and
rolling terrain with a high soil clay component. In
the lower areas and swales where the basin
subspecies dominates, sagebrush is tall, abundant,
and apparently vigorous.
The composition of the northern Yellowstone
mule deer herd has been estimated each year since
1990 using a helicopter. These surveys show a
steady increase in the proportion of adult males in
the herd, presumably in response to modifications
of hunting regulations promulgated by the Montana
Department of Fish, Wildlife and Parks.
PRONGHORN
Early accounts of the greater Yellowstone
ecosystem report large numbers of pronghorn in all
the major river valleys radiating out from the
present park area (Figure 7.9). Agriculture,
settlement, and market hunting were probably
responsible for the demise of these large, continuous
populations. Many accounts of the northern
range prior to 1882 also mention frequent sightings
of pronghorn, but these are reports of summering
animals (Schullery and Whittlesey 1992). It does
not appear that the park contains significant winter
range for pronghorn; their winter range is at lower
elevations downstt'eam of the north park boundary,
where they are competing with a growing amount
of human activity and development (Figure 7.10).
Pronghorn is a species of special interest on
the northern range because their numbers have at
times been very low, causing concerns over their
genetic wellbeing and even their long-term survival
as a population entity (Appendix B) (Barmore
1980, Houston 1982, O'Gara 1990, Scott and
Geisser 1996). Lee et al. (1994) added a further
reason for special interest: Yellowstone pronghorn
carry a unique genetic element (mtDNA haplotype
J) found in no other pronghorn herd in the west.
Surprisingly, the Yellowstone pronghorn contains
more genetic diversity than any other North
American herd studied, yet has never received
stocked pronghorn from elsewhere. The authors
stated:
The pronghorn herd of Yellowstone
National Park is one of the few remaining
undisturbed populations. The most
parsimonious explanation for the great
amount of mtDNA variation in the
Yellowstone herd is that Yellowstone
was a refuge when other herds were
exterminated or greatly reduced. This
genetic resource should be conserved.
Yellowstone pronghorn populations of 550 to
700 were reported in the 1930s, and these increased
to 600 to 800 in the 1940s following the addition of
Figure 7.9.
Pronghorn were
extremely abundant
in the lower river
valleys of greater
Yellowstone prior to
the creation of the
park in 1872.
Because of its small
sile alld isolation,
the northern
YellowstOlle
pronghorn
population is at
some risk of
extinction. NPS
photo.