| Number | Percentage
Food Item | of | of total
| occurrences | items
----------------------------+-------------+------------
_Sylvilagus_ sp. | 32 | 12.65
_Spermophilus variegatus_ | 5 | 1.97
_Eutamias_ sp. | 12 | 4.74
_Reithrodontomys megalotis_ | 4 | 1.58
_Peromyscus boylei_ | 2 | 0.79
_Peromyscus maniculatus_ | 3 | 1.18
_Peromyscus truei_ | 7 | 2.76
_Neotoma cinerea_ | 2 | 0.79
_Neotoma mexicana_ | 9 | 3.56
_Neotoma albigula_ | 5 | 1.97
_Neotoma_ sp. | 3 | 1.18
_Microtus longicaudus_ | 1 | 0.39
_Microtus mexicanus_ | 11 | 4.34
_Microtus montanus_ | 1 | 0.39
_Microtus_ sp. | 1 | 0.39
_Odocoileus hemionus_ | 59 | 23.32
Grass | 34 | 13.44
Juniper berries | 23 | 9.09
Pinyon needles | 14 | 5.53
Pinyon nuts | 1 | 0.39
Arthropods | 7 | 2.76
Juniper needles | 3 | 1.18
Rodent or Lagomorph bones | 5 | 1.97
_Sceloporus_ sp. | 1 | 0.39
Unidentified fruit | 2 | 0.79
Rocks | 3 | 1.18
Paper | 4 | 1.58
Soil | 3 | 1.18
Feathers | 5 | 1.97
+-------------+------------
Total | 253 |
----------------------------+-------------+------------
Hawks, owls and eagles live in the park. Red-tailed hawks were seen
frequently in the burned area on the northern end of Wetherill Mesa.
Both hawks and owls probably prey upon _Peromyscus_ in Mesa Verde, for
they are well-known predators upon mice and small rodents in other
areas. I tried to find owl and hawk nests that were occupied, but
located only nests that were abandoned or impossible to reach.
Captive gopher snakes, _Pituophis melanoleucus_, ate adults of both
species of _Peromyscus_. Gopher snakes probably are the most abundant
snake in the park; they feed mostly on mice and other rodents. Fur of
_Peromyscus_ was found in the stomach of a striped whipsnake,
_Masticophis taeniatus_ (Douglas, 1966:734).
DISCUSSION
Five species of _Peromyscus_ inhabit Mesa Verde National Park (Anderson,
1961). Two of these species, _P. crinitus_ and _P. difficilis_ are rare,
and none was taken in more than 14,000 trap nights. Several individuals
of _P. boylei_ were taken in live traps, but this species could not be
regarded as common. The two remaining species, _P. truei_ and _P.
maniculatus_, are the most abundant species in the park. Comparison of
the habitats and life-cycles of these two forms and analyses of their
interrelationships have been the objectives of this study.
The distribution of _P. truei_ in the park is regulated by the presence
of living pinyon-juniper woodland where logs and hollow trees of
_Juniperus osteosperma_ provide nesting and hiding places, and where
seeds of juniper trees and nuts of pinyon trees provide food. Several
other investigators have reported _P. truei_ to be associated with
trees, but apparently these findings have not assumed the importance
they warrant in understanding the ecology of this species. Bailey
(1931:152) observed an individual of _P. truei_ nesting in a tree on
Conchas Creek, New Mexico, and thought that this species might be more
arboreal than was generally supposed. The type specimen of _P. t. truei_
was taken by Shufeldt from a "nest protruding from an opening in the
dead and hollow trunk of a small pinon, at least 2 feet above the
ground.... The nest, composed of the fine fibers of the inner bark of
the pinon, was soon pulled out, and its owner dislodged...." (Shufeldt,
1885:403). Individuals of _P. truei_ usually build nests in trees, or in
hollow logs, and are therefore more abundant in pinyon-juniper woodland
where there are many such nesting sites.
Rocks and stones are not necessary in the habitat of _P. truei_,
although this species was most abundant where there was stony soil. The
coincidence of rock or stones and a high density of _P. truei_ is
thought to be explainable in terms of vegetation. Stony soils support
mixed shrubs as well as pinyon and juniper trees; the additional cover
and source of food probably allow a greater abundance of _P. truei_ than
would be possible without the shrubs. Secondarily, the rock provides
nesting sites for more mice.
Stands of mixed shrubs, lacking a pinyon-juniper canopy, do not support
_P. truei_. Its absence was noteworthy on Navajo Hill and on the
northern end of Wetherill Mesa where only _P. maniculatus_ lived among
the mixed shrubs and grassland. On the Mesa Verde, pinyon and juniper
trees must be present in order for _P. truei_ to live in an area; and,
these trees must be alive. Dead pinyons and junipers still stand in the
burned part of Morfield Ridge, but no _P. truei_ were found there.
Although a few individuals of _P. truei_ were taken in stands of
sagebrush adjacent to pinyon-juniper woodlands, this species does not
ordinarily venture far from the forest.
_P. maniculatus_ lives almost everywhere in Mesa Verde; the preferred
habitats are open and grassy with an overstory of mixed shrubs.
Individuals of _P. maniculatus_ venture into ecotonal areas lying
between grasslands and pinyon-juniper forest, or between sagebrush and
pinyon-juniper forest. _P. maniculatus_ is found also in disturbed areas
and in stands of sagebrush that occur in clearings of the pinyon-juniper
woodland. In such areas, _P. maniculatus_ and _P. truei_ are sympatric;
their home ranges overlap and any inter-specific competition that might
occur would be expected in these places.
The ability of _P. maniculatus_ to live in many different habitats is
correlated in part with its ability to build nests in a variety of
sites. Whereas _P. truei_ usually builds nests only in dead branches or
logs, _P. maniculatus_ builds nests in such varied places as spaces
under rocks, at the bases of rotten trees, and in abandoned tunnels of
pocket gophers. This adaptability is advantageous for the dispersal of
young individuals and the movement of adults into new areas.
Nesting sites have important bearing on survival of the young. In Mesa
Verde the rainy season occurs in July and August, while both species of
_Peromyscus_ are reproducing. It is reasonable to assume that young
animals that remain dry survive better than those that become wet and
chilled. The nestling young of _P. truei_ are in a more favorable
position to remain dry and warm than are nestling young of _P.
maniculatus_.
Captives of each species differed in the amounts of water consumed per
gram of body weight. Individuals of _P. truei_ consumed more water per
gram of body weight than individuals of _P. maniculatus_. Animals may
drink more water than they require when allowed to drink _ad libitum_,
but Lindeborg (1952) has shown that species which consume less water
when it is not restricted also fare better on a reduced ration. _P.
maniculatus_ appears to be better adapted to aridity than _P. truei_.
The preferred habitats of each species are in accord with these
findings.
Within the trapping grid, the most moderate microenvironment, in terms
of temperature and humidity, was in the pinyon-juniper forest, where
_P. truei_ lives. The temperature extremes were wider in the
microenvironments of a thicket of oak brush and of two different stands
of sagebrush, where _P. maniculatus_ lives, than in the forest. _P.
maniculatus_ tends to live in the harsher, more arid parts of Mesa
Verde. Because of its propensity to build nests under things, or in the
ground, and because of its ability to use less water per gram of body
weight, _P. maniculatus_ is better adapted to withstand harsh
environments than is _P. truei_.
_P. truei_ may be restricted to the pinyon-juniper woodland because of
its need for more mesic conditions. Still, Mesa Verde is semi-arid and
there are few permanent sources of water available for animals. The
primary source of moisture for rodents must be their food. Analysis of
the percentages of moisture contained in the three most common plants in
the trapping grid showed that _P. truei_ could obtain the required
moisture by eating about ten grams of these plants daily; individuals of
_P. maniculatus_ would need to eat less in order to satisfy their water
needs.
Individuals of _P. truei_ died more frequently in warm live-traps than
did individuals of _P. maniculatus_. This indicates that _P. truei_ can
tolerate less desiccation, or a narrower range of temperatures, than can
_P. maniculatus_.
Both species of mice eat some of the same plants, but these plants occur
widely. _P. truei_ seems to rely more upon the nuts of pinyons and the
seeds of junipers than does _P. maniculatus_. Mounds of discarded
juniper seeds were associated with all nesting sites of _P. truei_.
Bailey (1931:153) also noticed the fondness of this species for pine
nuts and juniper seeds. Apparently, the availability of these foods is
one of the major factors affecting the distribution of _P. truei_.
However, this is not the only factor, as is shown by the presence of _P.
maniculatus_ but lack of _P. truei_ in a juniper-pinyon association with
an understory of bitterbrush. This habitat was seemingly too arid for
_P. truei_.
Factors Affecting Population Densities
The production of young, and success in rearing them, is essential to
continuity of any population. _P. maniculatus_ is favored in this
respect, because the females produce more young and wean them sooner
than do females of _P. truei_. In addition, lactating females of _P.
maniculatus_ require significantly less water than do females of _P.
truei_. Since young mice of both species require no more water per gram
of body weight than do adults, the young can disperse into any area that
is habitable by their species. _P. maniculatus_ probably is affected
less by prolonged drought than is _P. truei_. Since lactating females
require the most water of any animal in the population, they are the
weakest link in the system. Females of _Peromyscus_ are known to
reabsorb embryos when conditions are unfavorable for continued
pregnancy. If prolonged drought occurred in the reproductive season, and
desiccated the vegetation upon which the mice depend for moisture, the
populations should diminish the following year. Lactating females of _P.
truei_ would be affected more seriously by a shortage of water than
would lactating females of _P. maniculatus_.
Of two species, the one producing the more young probably would be
subjected to more parasitism and predation than the species producing
fewer young. A favorable season for botflies, _Cuterebra_ sp., revealed
that _P. maniculatus_ has a higher incidence of parasitism by these
flies than has _P. truei_; possibly the adult flies concentrate in the
open, grassy areas where _P. maniculatus_ is more abundant, rather than
in the woodlands where _P. truei_ lives. Perhaps the lower parasitism of
_P. truei_ by warbles is related to the physiology of this species of
mouse. Near Boulder, Colorado, the incidence of infection by warbles is
lower in _P. difficilis_, a species closely related to _P. truei_, than
in _P. maniculatus_ (V. Keen, personal communication).
Although predation by carnivores would be expected to be higher on _P.
maniculatus_, because this species does not climb, my data show that
more individuals of _P. truei_ were taken by coyotes. I lack confidence
in these findings, suspecting that another sample might indicate the
reverse. Birds of prey probably catch more individuals of _P.
maniculatus_, because this species lives in more open habitats. My data
do not warrant firm conclusions regarding predation.
The length of time females must care for their young influences the rate
at which individuals can be added to the population. Females of _P.
truei_ nurse their young longer and keep them in the nest longer than do
females of _P. maniculatus_. Although this may enhance the chances of
survival of young of _P. truei_, it also reduces the number of litters
that each female can have in each breeding season. Females of _P.
maniculatus_ can produce more young per litter, and each female probably
can produce more litters per year than females of _P. truei_.
Captives of _P. truei_ were tolerant of other individuals of the same
species, even when kept in close confinement. However, when there was
slight shortage of food or water they killed their litter mates, or
females killed their young. Only a short period of time was necessary
for one mouse to dispatch all others in the litter. The attacked mice
were bitten through the head before being eaten; the brains and viscera
were the first parts consumed. The population might be decimated rapidly
if drought forced this species to cannibalism. When the supply of food
or water was restored, the captive mice resumed their tolerant nature.
In captivity, _P. maniculatus_ is amazingly tolerant of close
confinement with members of the same species; individuals did not tend
to kill their litter mates, or their young, even during shortage of food
and water. This tolerance, especially under stressful conditions,
probably enables _P. maniculatus_ to persist in relatively unfavorable
areas.
Adaptations to Environment
Each of the two species of _Peromyscus_ illustrates one or more
adaptations to its environment. _P. truei_ is adapted to climbing by
possession of long toes, a long tail, and large hind feet. The tail is
used as a counterbalance when climbing (Horner, 1954). When frightened,
individuals of _P. truei_ often ran across the ground in a
semi-saltatorial fashion, bounding over clumps of grass that were as
much as 18 inches high. Such individuals usually ran to the nearest tree
and climbed to branches 10 to 20 feet above the ground.
Large eyes are characteristic of the _truei_ group of mice, and may be
an adaptation to a semi-arboreal mode of life. A similar adaptation is
shared by some other arboreal mammals, and of arboreal snakes. The large
eyes of _P. truei_ in comparison to those of _P. maniculatus_, probably
increase the field of vision, and permit the animal to look downward as
well as in other directions.
The above-mentioned adaptations of _P. truei_ permit these graceful mice
to use their environment effectively. By climbing, this species can nest
above-ground in the hollow branches of trees, and can rear its young in
a comparatively safe setting. The ability to climb also permits vertical
as well as horizontal use of a limited habitat. Because of the
three-dimensional nature of the home range of _truei_, its range is
actually larger than that of _maniculatus_ although the standard
trapping procedures makes the home range of the two appear to be about
the same size. Finally, trees may offer safety from predators, and a
source of food that probably is the winter staple of this species.
_Peromyscus maniculatus_ has adapted differently to its environment.
Small size of body and appendages permit this species to use a variety
of nesting sites and hiding places even though it is restricted, by its
anatomy, to life on the ground. The tail and hind feet are shorter than
in _P. truei_, and _P. maniculatus_ is an inefficient climber. I have
placed individuals in bushes, and found that many walk off into space
from a height of several feet. Perhaps the relative smallness of their
eyes accounts for their seeming lack of awareness of how high they are
above the ground.
When frightened, individuals of _P. maniculatus_ ran rapidly in a
zig-zag path and dove into the nearest cover. Mice, released from live
traps, often stuck their heads under leaves, leaving their bodies
exposed. This species tends to hide as rapidly as possible, and remain
motionless. This tactic would not be of much value as an escape from
carnivores, but it could be effective against birds of prey.
In Mesa Verde, _P. maniculatus_ inhabits the more arid, open areas. When
the population is dense, individuals of this species are found also in
pinyon-juniper woodland. Apparently _P. maniculatus_ prefers the grassy
areas and the thickets of oak brush. Although such habitats have harsh
climatic conditions, they offer innumerable hiding places, and thus have
great advantage for a species confined to the ground.
The low requirements of water per gram of body weight, the ability to
eat diversified foods, the use of varied habitats, the high fecundity,
and the ability to use any nook for retreat or nesting make _P.
maniculatus_ a successful inhabitant of most parts of Mesa Verde, and
indeed, of most of North America.
LITERATURE CITED
ANDERSON, S.
1961. Mammals of Mesa Verde National Park, Colorado. Univ. Kansas
Publ., Mus. Nat. Hist., 14:29-67, 2 pls., 3 figs.
ARRHENIUS, G., and E. BONATTI
1965. The Mesa Verde loess, pp. 92-100, _in_ Contributions of the
Wetherill Mesa Archeological Project, Memoirs Soc. Amer.
Archeol., 19; American Antiquity, 31, No. 2, Pt. 2.
ASDELL, S. A.
1964. Patterns of mammalian reproduction. Comstock Publ. Co.,
Ithaca, viii + 1-670 pp.
BAILEY, V.
1931. Mammals of New Mexico. N. Amer. Fauna, 53:1-412, 22 pls.,
58 figs.
BEIDLEMAN, R. G.
1954. October breeding of _Peromyscus_ in north central Colorado.
Jour. Mamm., 35:118.
BRUSVEN, M. A., and G. B. MULKERN
1960. The use of epidermal characteristics for the identification
of plants recovered in fragmentary condition from the crops
of grasshoppers. North Dakota Agricultural Exp. Sta., Fargo,
Research Rept., 3:3-11.
BURT, W. H.
1940. Territorial behavior and populations of some small mammals in
southern Michigan. Misc. Publ. Mus. Zool., Univ. Michigan, 45:
1-58, 2 pls.
CALHOUN, J. B., ed.
1948-1956. Annual reports of the North American census of small
mammals. Distributed by the editor, National Institutes of
Health, Bethesda 14, Maryland.
1959. Population dynamics of vertebrates release No. 10, Revised
sampling procedure for the North American census of small
mammals (NACSM). pp. 1-12, Distributed by the editor,
Nat. Inst. Health, Bethesda 14, Maryland.
CHEW, R. M.
1951. The water exchanges of some small mammals. Ecological
Monographs, 21:215-225.
1965. Water metabolism of mammals, pp. 43-178, _in_ Physiological
Mammology Vol. II Mammalian reactions to stressful environments,
Mayer, W. V., and R. G. Van Gelder, eds., Academic Press,
New York, xii + 1-326 pp.
COGSHALL, A. S.
1928. Food habits of deer mice of the genus _Peromyscus_ in
captivity. Jour. Mamm., 9:217-221.
COLLINS, H. H.
1918. Studies of normal molt and of artificially induced
regeneration of pelage in _Peromyscus_. Jour. Exptl. Zool.,
27:73-99.
DICE, L. R.
1922. Some factors affecting the distribution of the prairie vole,
forest deer mouse, and prairie deer mouse. Ecology, 3:29-47.
1934. An improved _Peromyscus_ ration. Jour. Mamm., 15:160-161.
DOUGLAS, C. L.
1965. Biological techniques in archeology, pp. 193-201, _in_
Contributions of the Wetherill Mesa Archeological Project,
Memoirs Soc. Amer. Archeol., 19; American Antiquity, 31,
No. 2, Pt. 2.
1966. Amphibians and reptiles of Mesa Verde National Park,
Colorado. Univ. Kansas Publ. Mus. Nat. Hist., 15:711-744,
2 pls., 6 figs.
DUSI, J. L.
1949. Methods for the determination of food habits by plant
microtechnique and histology and their application to cottontail
rabbit food habits. Jour. Wildlife Mgt., 13:295-298
ERDMAN, J. A.
1962. Ecology of the pinyon-juniper woodland of Wetherill Mesa,
Mesa Verde National Park, Colorado. Unpublished M. A. thesis,
Univ. Colorado.
ERDMAN, J. A., C. L. DOUGLAS, and J. W. MARR
1968. The environment of Mesa Verde, Mesa Verde National Park,
Colorado. Archeol. Res. Series, No. 7-D. Nat. Park Serv.,
Washington, D. C., in press.
ESAU, K.
1960. Anatomy of Seed Plants. John Wiley and Sons, New York, xvi +
1-376 pp.
GEIGER, R.
1965. The climate near the ground. Harvard Univ. Press, Cambridge,
Mass., xiv + 1-611 pp.
HALL, E. R.
1928. Note on the life history of the woodland deer mouse. Jour.
Mamm., 9:255-256
HAMILTON, W. J., JR.
1941. The food of small forest mammals in eastern United States.
Jour. Mamm., 22:250-263
HAYNE, D. W.
1949. Calculation of size of home range. Jour. Mamm., 30:1-18.
HOFFMEISTER, D. F.
1951. A taxonomic and evolutionary study of the pinon mouse,
_Peromyscus truei_. Illinois Biol. Monographs, Vol. 21, No. 4,
ix + 1-104 pp.
HORNER, B. E.
1954. Arboreal adaptations of Peromyscus with special reference to
use of the tail. Cont. Lab. Vert. Biol., Univ. Michigan,
61:1-85.
HOWARD, W. E.
1950. Winter fecundity of caged male white-footed mice in Michigan.
Jour. Mamm., 31:319-321.
JAMESON, E. W., JR.
1952. Food of deer mice _Peromyscus maniculatus_ and _P. boylei_ in
the northern Sierra Nevada, California. Jour. Mamm., 33:50-60.
1953. Reproduction of deer mice (_Peromyscus maniculatus_ and
_P. boylei_) in the Sierra Nevada, California. Jour. Mamm.,
34:44-58.
JOHNSON, D. R.
1962. Effects of habitat change on the food habits of rodents.
Abstract of Ph. D. dissertation, Colorado State Univ.,
Ft. Collins.
LANG, H.
1925. How squirrels and other rodents carry their young. Jour.
Mamm., 6:18-24.
LINDEBORG, R. G.
1950. An adaptation of breeding _Peromyscus maniculatus bairdii_
females to available water, and observations on changes in
body weight. Jour. Mamm., 31:74-78.
1952. Water requirements of certain rodents from xeric and mesic
habitats. Cont. Lab. Vert. Biol., Univ. Michigan, 58:1-32.
MCCABE, T. T., and B. D. BLANCHARD
1950. Three species of _Peromyscus_. Rood Associates, Santa
Barbara, California, v + 1-136 pp.
METCALFE, C. R., and L. CHALK
1950. Anatomy of the dicotyledons I and II. Clarendon Press,
Oxford, 1500 pp.
MOHR, C. O., and W. A. STUMPF
1966. Comparison of methods for calculating areas of animal
activity. Jour. Wildlife Mgt., 30:293-304.
OSGOOD, W. H.
1909. Revision of the mice of the American genus _Peromyscus_.
N. Amer. Fauna, 28:1-285, 8 pls., 12 figs.
REDMAN, J. P., and J. A. SEALANDER
1958. Home ranges of deer mice in southern Arkansas. Jour. Mamm.,
39:390-395.
ROSS, L. G.
1930. A comparative study of daily water-intake among certain
taxonomic and geographic groups within the genus _Peromyscus_.
Biol. Bull., 59:326-338.
SANDERSON, G. C.
1966. The study of mammal movements--a review. Jour. Wildlife Mtg.,
30:215-235.
SCHMIDT-NIELSEN, K.
1964. Desert animals: physiological problems of heat and water.
Oxford Univ. Press, London, xv + 1-277 pp.
SCHMIDT-NIELSEN, K., B. SCHMIDT-NIELSEN, and A. BROKAW
1948. Urea excretion in desert rodents exposed to high protein
diets. Jour. Cell. Comp. Physiol., 32:361-379.
SCOTT, T. G., and E. SNEAD
1942. Warbles in _Peromyscus leucopus noveboracensis_. Jour. Mamm.,
23:94-95.
SEALANDER, J. A.
1961. Hematological values in deer mice in relation to botfly
infection. Jour. Mamm., 42:57-60.
SETON, E. T.
1920. Notes on the breeding habits of captive deer mice. Jour.
Mamm., 1:134-138.
SHUFELDT, R. W.
1885. Description of Hesperomys truei, a new species belonging to
the subfamily Murinae. Proc. U. S. Nat. Mus., 8:403-408, 21 pls.
STICKEL, L. F.
1954. A comparison of certain methods of measuring ranges of small
mammals. Jour. Mamm., 35:1-15.
SVIHLA, A.
1932. A comparative life history study of the mice of the genus
_Peromyscus_. Univ. Michigan Mus. Zool., Misc. Publ., 24:1-39.
TEST, F. H., and A. R. TEST
1943. Incidence of dipteran parasitosis in populations of small
mammals. Jour. Mamm., 24:506-508.
WELSH, S. L., and J. A. ERDMAN
1964. Annotated checklist of the plants of Mesa Verde, Colorado.
Brigham Young Univ. Sci. Bull., Biol. Ser., 4(2):1-32.
WILLIAMS, O.
1955. The food of mice and shrews in a Colorado montane forest.
Univ. Colorado Studies, Ser. in Biol., 3:109-114.
1959a. Food habits of the deer mouse. Jour. Mamm., 40:415-419.
1959b. Water intake in the deer mouse. Jour. Mamm., 40:602-606.
1959c. Modified gum syrup. Turtox News, Vol. 37, No. 10.
WILSON, L. W.
1945. Parasites collected from wood mouse in West Virginia. Jour.
Mamm., 26:200.
* * * * *
Transcriber's Notes
All obvious typographic errors corrected. The notation [=Y] in Table 10
represents the Mean Value for that column. The notation H_{2}O
represents the water molecule where the _{2} represents the subscripted
2. The notation 8-1/2 represents 8 and one half.
Page Correction
==== ==============
429 nuaseosus => nauseosus
430 Orthocarpos => Orthocarpus
450 ludovociana => ludoviciana
456 phrheliometer => pyrheliometer
480 rudale => ruderale
481 rates => rats
482 bases => basis
499 clumbs => clumps