The distributions of animals are influenced by geographic, vegetational,
and altitudinal factors. The Mesa Verde is intermediate in geographic
position and altitude between the high Southern Rocky Mountains and the
low southwestern desert. For this reason, we find on the Mesa Verde (1)
a preponderance of species having wide distributions in this part of the
country, and having relatively wide ranges of tolerance for different
habitats, (2) a lesser number of exclusively montane or boreal species
than occur in the higher mountains to the northeast of the Mesa and that
may reach the limits of their ranges here, and (3) a small number of
species of southern or Sonoran affinities. Fifty-four species are
recorded above.
Forty-one of these species are represented by specimens from the Park.
Thirteen additional species in the list have been seen in the Park.
On the Grand Mesa, which is more elevated than, and some 110 miles north
of, the Mesa Verde (see Figure 1), 55 per cent of the species of mammals
have boreal affinities and the other 45 per cent are wide-spread species
(Anderson, 1959:414). Boreal species from the Mesa Verde are _Sorex
vagrans_, _Sylvilagus nuttallii_, _Spermophilus lateralis_, _Marmota
flaviventris_, _Tamiasciurus hudsonicus_, _Microtus montanus_, and
_Microtus longicaudus_. These seven species comprise only thirteen per
cent of the mammalian fauna of the Mesa Verde. Other boreal species that
occur in the mountains of Colorado on the Grand Mesa or elsewhere
(Findley and Anderson, 1956:80) and that do not occur on the Mesa Verde
are _Sorex cinereus_, _Sorex palustris_, _Ochotona princeps_, _Lepus
americana_, _Clethrionomys gapperi_, _Phenacomys intermedius_, _Zapus
princeps_, _Martes americana_, _Mustela erminea_, and _Lynx canadensis_.
The 47 species from the Mesa Verde that are not exclusively boreal make
up 87 per cent of the mammalian fauna. Most of these are wide-spread
species and are more abundant in the deserts or other lowlands than in
the coniferous forests of the highlands, for example the eight species
of bats, and _Sylvilagus audubonii_, _Thomomys bottae_, _Taxidea taxus_,
_Bassariscus astutus_, _Canis latrans_, _Cynomys gunnisoni_,
_Reithrodontomys megalotis_, and _Lepus californicus_. A few of the
wide-spread species are more common in the highlands than in the
lowlands, for example _Ursus americanus_, _Felis concolor_, _Castor
canadensis_, _Erethizon dorsatum_, and _Cervus canadensis_, and the
ranges of three of these, the bear, mountain lion and wapiti, are more
restricted today than formerly. A few species find their favorite
habitat and reach their greatest abundance in altitudinally and
vegetationally intermediate areas such as upon the Mesa Verde, or in
special habitats, such as the rock ledges, and crevices that are so
abundant on the Mesa. Examples of this group of species are
_Spermophilus variegatus_, _Peromyscus crinitus_, _Peromyscus truei_,
_Neotoma cinerea_, and _Neotoma mexicana_. One species, _Dipodomys
ordii_, is restricted to the desert. Species that are restricted to the
desert and that occur in Montezuma County, Colorado, but that are not
known from the Mesa Verde are _Ammospermophilus leucurus_, _Perognathus
flavus_, and _Onychomys leucogaster_.
Species known to have changed in numbers in the past 50 years are the
mule deer that has increased, and the prairie dog that has decreased.
Possibly beaver have increased along the Mancos River. The muskrat,
mink, beaver, and raccoon usually occur only along the Mancos River, as
there is no other permanent surface water in the Park.
Species such as the bighorn and the marmot that are rare within the
Park, or those such as the chickaree, the prairie dog, the wandering
shrew, the montane vole, and the long-tailed vole that occupy only small
areas of suitable habitat within the Park are the species most likely to
be eliminated by natural changes, or through the activities of man. For
example parasites introduced through domestic sheep that wander into the
range of bighorns within the Park might endanger the bighorn population.
An increase in grazing activity, road building, and camping in Prater
and Morfield canyons might eliminate the small areas of habitat occupied
by the montane vole and the wandering shrew. Fire in Chickaree Draw
could destroy all the Douglas fir there, and consequently much of the
habitat occupied by the chickaree.
Probably some species inhabit the Mesa that have not yet been found, but
they are probably few, and their discovery will not alter the faunal
pattern in which the few boreal species occupy restricted habitats in
the higher parts of the Mesa, and a preponderance of geographically
wide-spread species occupy all or most of the Mesa, and surrounding
areas. Additional bats are the species most likely to be added to the
list.
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