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UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY
Volume 18, No. 5, pp. 421-504
August 20, 1969
Comparative Ecology of Pinyon Mice
and Deer Mice in
Mesa Verde National Park, Colorado
BY
CHARLES L. DOUGLAS
UNIVERSITY OF KANSAS
LAWRENCE
1969
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
Editors of this number: Frank B. Cross, Philip S. Humphrey,
J. Knox Jones, Jr.
Volume 18, No. 5, pp. 421-504
Published August 20, 1969
UNIVERSITY OF KANSAS
Lawrence, Kansas
PRINTED BY
ROBERT R. (BOB) SANDERS, STATE PRINTER
TOPEKA, KANSAS
1969
[Illustration]
32-6879
CONTENTS
PAGE
INTRODUCTION 424
Physiography 425
Vegetation and Climate 427
ACKNOWLEDGMENTS 427
DESCRIPTIONS OF MAJOR TRAPPING LOCALITIES 428
HOME RANGE 435
Calculations of Home Range 437
Analysis by Inclusive Boundary Strip 439
Analysis by Exclusive Boundary Strip 440
Adjusted Length of Home Range 440
Distance Between Captures 441
VEGETATIONAL ANALYSIS OF HABITATS 446
MICROCLIMATES OF DIFFERENT HABITATS 450
HABITAT PREFERENCE 459
NESTING AND NEST CONSTRUCTION 461
REPRODUCTION 465
GROWTH 469
PARENTAL BEHAVIOR 471
Transportation of Young 472
CHANGES OWING TO INCREASE IN AGE 475
ANOMALIES AND INJURIES 476
Losses Attributed to Exposure in Traps 477
Dental Anomalies 478
Anomalies in the Skull 478
FOOD HABITS 479
WATER CONSUMPTION 482
PARASITISM 491
PREDATION 493
DISCUSSION 495
Factors Affecting Population Densities 497
Adaptations to Environment 499
LITERATURE CITED 501
INTRODUCTION
Centuries ago in southwestern Colorado the prehistoric Pueblo
inhabitants of the Mesa Verde region expressed their interest in mammals
by painting silhouettes of them on pottery and on the walls of kivas.
Pottery occasionally was made in the stylized form of animals such as
the mountain sheep. The silhouettes of sheep and deer persist as
pictographs or petroglyphs on walls of kivas and on rocks near
prehistoric dwellings. Mammalian bones from archeological sites reveal
that the fauna of Mesa Verde was much the same in A. D. 1200, when the
Pueblo Indians were building their magnificent cliff dwellings, as it is
today. One of the native mammals is the ubiquitous deer mouse,
_Peromyscus maniculatus_. The geographic range of this species includes
most of the United States, and large parts of Mexico and Canada.
Another species of the same genus, the pinyon mouse, _P. truei_, also
lives on the Mesa Verde. The pinyon mouse lives mostly in southwestern
North America, occurring from central Oregon and southern Wyoming to
northern Oaxaca. This species generally is associated with pinyon pine
trees, or with juniper trees, and where the pinyon-juniper woodland is
associated with rocky ground (Hoffmeister, 1951:vii).
_P. maniculatus rufinus_ of Mesa Verde was considered to be a mountain
subspecies by Osgood (1909:73). The center of dispersion for _P. truei_
was in the southwestern United States, and particularly in the Colorado
Plateau area (Hoffmeister, 1951:vii). The subspecies _P. truei truei_
occurs mainly in the Upper Sonoran life-zone, and according to
Hoffmeister (1951:30) rarely enters the Lower Sonoran or Transition
life-zones. _P. maniculatus_ and _P. truei_ are the most abundant of the
small mammals in Mesa Verde National Park, which comprises about
one-third of the Mesa Verde land mass.
Under the auspices of the Wetherill Mesa Archeological Project, the
flora of the park recently was studied by Erdman (1962), and by Welsh
and Erdman (1964). These studies have revealed stands of several
distinct types of vegetation in the park and where each type occurs.
This information greatly facilitated my study of the mammals inhabiting
each type of association. The flora and fauna within the park are
protected, in keeping with the policies of the National Park Service,
and mammals, therefore, could be studied in a relatively undisturbed
setting.
Thus, the abundance of these two species of _Peromyscus_, the botanical
studies that preceded and accompanied my study, the relatively
undisturbed nature of the park, and the availability of a large area in
which extended studies could be carried on, all contributed to the
desirability of Mesa Verde as a study area.
My primary purpose in undertaking a study of the two species of
_Peromyscus_ was to analyze a number of ecological factors influencing
each species--their habitat preferences, how the mice lived within their
habitats, what they ate, where they nested, what preyed on them, and how
one species influenced the distribution of the other. In general, my
interest was in how the lives of the two species impinge upon each other
in Mesa Verde.
Physiography
The Mesa Verde consists of about 200 square miles of plateau country in
southwestern Colorado, just northeast of Four Corners, where Colorado,
New Mexico, Arizona and Utah meet. In 1906, more than 51,000 acres of
the Mesa Verde were set aside, as Mesa Verde National Park, in order to
protect the cliff dwellings for which the area is famous.
The Mesa Verde land mass is composed of cross-bedded sandstone strata
laid down by Upper Cretaceous seas. These strata are known locally as
the Mesaverde group, and are composed, from top to bottom, of Cliff
House sandstone, the Menefee formation, the Point Lookout sandstone, the
well known Mancos shale, and the Dakota sandstone, the lowest member of
the Cretaceous strata. The Menefee formation is 340 to 800 feet thick,
and contains carbonaceous shale and beds of coal.
There are surface deposits of Pleistocene and Recent age, with gravel
and boulders of alluvial origin; colluvium composed of heterogeneous
rock detritus such as talus and landslide material; and alluvium
composed of soil, sand, and gravel. A layer of loess overlays the
bedrock of the flat mesa tops in the Four Corners area. The earliest
preserved loess is probably pre-Wisconsin, possibly Sangamon in age
(Arrhenius and Bonatti, 1965:99).
The North Rim of Mesa Verde rises majestically, 1,500 feet above the
surrounding Montezuma Valley. Elevations in the park range from 8,500
feet at Park Point to about 6,500 feet at the southern ends of the
mesas. The Mesa Verde land mass is the remnant of a plateau that erosion
has dissected into a series of long, narrow mesas, joined at their
northern ends, but otherwise separated by deep canyons. The bottoms of
these canyons are from 600 to 900 feet below the tops of the mesas.
The entire Mesa Verde land mass tilts southward; Park Headquarters, in
the middle of Chapin Mesa (Fig. 1), is at about the same elevation as is
the entrance of the park, 20 miles by road to the north.
[Illustration: FIG. 1: Map of Mesa Verde National Park and vicinity,
showing major trapping localities from 1961-1964. Trapping
localities are designated in the text as follows: 1) North End
Wetherill Mesa 2) Rock Springs 3) Mug House 4) Bobcat Canyon
Drainage 5) North of Long House 6) Juniper-Pinyon-Bitterbrush
Site 7) Navajo Hill 8) West of Far View Ruins 9) South of Far
View Ruins, also general location of trapping grid 10) M-2
Weather Station 11) East Loop Road Site 12) Big Sagebrush Stand,
Southern end Chapin Mesa 13) Grassy Meadow, Southern end Moccasin
Mesa 14) Bedrock Outcroppings, Southern end Moccasin Mesa
15) 1/4 mi. SE Park Entrance 16) Meadow, 1 mi. SE Park Entrance
17) Morfield Ridge.]
Vegetation and Climate
Mesa Verde is characterized by pinyon-juniper woodlands that extend
throughout much of the West and Southwest. Although the pinyon-juniper
woodland dominates the mesa tops, stands of Douglas fir occur in some
sheltered canyons and on north-facing slopes. Thickets of Gambel oak and
Utah serviceberry cover many hillsides and form a zone of brush at
higher elevations in the park. Aspens grow in small groups at the base
of the Point Lookout sandstone and at a few other sheltered places where
the supply of moisture suffices. Individual ponderosa pine are scattered
through the park, and stands of this species occur on some slopes and in
the bottoms of some sheltered canyons.
Tall sagebrush grows in deep soils of canyon bottoms, and in some burned
areas, and was found to be a good indicator of prehistoric occupation
sites.
The climate of Mesa Verde is semi-arid, and most months are dry and
pleasant. Annual precipitation has averaged about 18.5 inches for the
last 40 years. July and August are the months having the most rainfall.
Snow falls intermittently in winter, and may persist all winter on
north-facing slopes and in valleys. In most years, snow is melting and
the kinds of animals that hibernate are emerging by the first of April.
Because of the great differences in elevation between the northern and
southern ends of the mesas, differences in climate are appreciable at
these locations. Winter always is the more severe on the northern end of
the park, owing to persistent winds, lower temperatures, and more snow.
The northern end of the park is closer to the nearby La Platta Mountains
where ephemeral storms of summer originate. They reach the higher
elevations of the park first, but such storms dissipate rapidly and are
highly localized. The northern end of the park therefore receives much
more precipitation in summer and winter than does the southern end.
The difference in precipitation and the extremes in weather between the
northern and southern ends of the mesas affect the distribution of
plants and animals. Species of mammals, plants, and reptiles are most
numerous on the middle parts of the mesas, as also are cliff-dwellings,
surface sites, and farming terraces of the prehistoric Indians.
Anderson (1961) reported on the mammals of Mesa Verde National Park, and
Douglas (1966) reported on the amphibians and reptiles. In each of these
reports, earlier collections are listed and earlier reports are
summarized.
I lived in Mesa Verde National Park for 28 months in the period July
1961 to September 1964, while working as Biologist for the Wetherill
Mesa Archeological Project, and the study here reported on is one of the
faunal studies that I undertook.
ACKNOWLEDGMENTS
This study could not have been completed without the assistance and
encouragement of numerous persons. I am grateful to Dr. Olwen Williams,
of the University of Colorado, for suggesting this study and helping me
plan the early phases of it.
Mr. Chester A. Thomas, formerly Superintendent, and Mrs. Jean Pinkley,
formerly Chief of Interpretation at Mesa Verde National Park, permitted
me to use the park's facilities for research, issued collecting permits,
and in 1965 appointed me as a research collaborator in order that I
might complete my studies.
Dr. H. Douglas Osborne, California State College, Long Beach, formerly
Supervisory Archeologist of the Wetherill Mesa Project, took an active
interest in my research and provided supplies, transportation and
laboratory and field assistance under the auspices of the Wetherill
Project. His assistance and encouragement are gratefully acknowledged.
Mrs. Marilyn A. Colyer of Mancos, Colorado, ably assisted in analyzing
vegetation in the trapping grid; Mr. Robert R. Patterson, the University
of Kansas, assisted me in the field in October of 1963 and in August of
1965. Mr. James A. Erdman, United States Geological Survey, Denver,
formerly Botanist for the Wetherill Mesa Project, and Dr. Stanley L.
Welsh, Brigham Young University, identified plants for me in the field,
and checked my identifications of herbarium specimens. I owe my
knowledge of the flora in the park to my association with these two
capable botanists.
I am grateful to the following persons for identification of
invertebrates: D. Eldon Beck, fleas and ticks; Paul Winston, mites; V.
Eugene Nelson, mites; William Wrenn, mites; Wayne W. Moss, mites;
William B. Nutting, mites (_Desmodex_); Marilyn A. Colyer, insects; John
E. Ubelaker, endoparasites; Veryl F. Keen, botflies. George A. King,
Architect, of Durango, Colorado, prepared the original map for Figure 1.
Mr. Harold Shepherd of Mancos, Colorado, Senior Game Biologist, Colorado
Department of Fish, Game and Parks, obtained permission for me to use
the department's trapping grid near Far View Ruins, and provided me with
preserved specimens of mice.
Mr. Fred E. Mang Jr., Photographer, National Park Service, processed
large numbers of photomicrographs of plant epidermis. Dr. Kenneth B.
Armitage, The University of Kansas, offered valuable suggestions for the
study of water consumption in the two species of _Peromyscus_, and
permitted me to use facilities of the Zoological Research Laboratories
at The University of Kansas. Dr. Richard F. Johnston, The University of
Kansas, permitted me to house mice in his controlled-temperature room at
the Zoological Research Laboratories. I am grateful to all of the above
mentioned persons for their aid.
I acknowledge with gratitude the guidance, encouragement, and critical
assistance of Professor E. Raymond Hall throughout the course of the
study and preparation of the manuscript. I also extend my sincere thanks
to Professors Henry S. Fitch, Robert W. Baxter, and William A. Clemens
for their helpful suggestions and assistance.
To my wife, Virginia, I am grateful for encouragement and assistance
with many time-consuming tasks connected with field work and preparation
of the manuscript.
Travel funds provided by the Kansas Academy of Science permitted me to
work in the park in August, 1965. The Wetherill Mesa Project was an
interdisciplinary program of the National Park Service to which the
National Geographic Society contributed generously. I am indebted to the
Society for a major share of the support that resulted in this report.
This is contribution No. 44 of the Wetherill Mesa Project.
DESCRIPTIONS OF MAJOR TRAPPING LOCALITIES
Trapping was begun in September of 1961 in order to analyze the
composition of rodent populations within the park. I used the method of
trapping employed by Calhoun (1948) in making the Census of North
American Small Mammals (N. A. C. S. M.). It consisted of two lines of
traps, each 1,000 feet long having 20 trapping stations that were 50
feet apart. The lines were either parallel at a distance of 400 feet
from each other, or were joined to form a line 2,000 feet long. Three
snap traps were placed within a five-foot radius of each station, and
were set for three consecutive nights. More than a dozen areas were
selected for extensive trapping (Fig. 1). Some of these were retrapped
in consecutive years in order to measure changes in populations.
One circular trapline of 159.5 feet radius was established in November
1961, and was tended for 30 consecutive days to observe the effect of
removing the more dominant species (Calhoun, 1959).
Other mouse traps and rat traps were set in suitable places on talus
slopes, rocky cliffs, and in cliff dwellings. Most of these traps were
operated for three consecutive nights.
In order to test hypotheses concerning habitat preferences of each of
the species of _Peromyscus_, several previously untrapped areas that
appeared to be ideal habitat for one species, but not for the other,
were selected for sampling. In the summers of 1963 and 1964 snap traps
were set along an arbitrary line through each of these areas. Traps were
placed in pairs; each pair was 20 feet from the adjacent pairs.
A mixture of equal parts of peanut butter, bacon grease, raisins, roman
meal and rolled oats was used as bait. Rolled oats or coarsely ground
scratch feed was used in areas where insects removed the mixture from
the traps.
Rodents trapped by me were variously prepared as study skins with
skulls, as flat skins with skulls, as skeletons, as skulls only, or as
alcoholics. Representative specimens were deposited in The University of
Kansas Museum of Natural History. In the course of my study, traps were
set in the following areas:
_Morfield Ridge_
In July 1959 a fire destroyed more than 2,000 acres of pinyon-juniper
forest (_Pinus edulis_ and _Juniperus osteosperma_) in the eastern part
of the park. The burned area extends from Morfield Canyon to Waters
Canyon, encompassing several canyons, Whites Mesa, and a ridge between
Morfield Canyon and Waters Canyon that is known locally as Morfield
Ridge (Fig. 1). Beginning on September 4, 1961, three pairs of traplines
were run on this ridge at elevations of 7,300 to 7,600 feet.
Vegetation in the trapping area consisted of dense growths of grasses
and herbaceous plants, which had covered the ground with seeds. In this
and in the following accounts, the generic and specific names of plants
are those used by Welsh and Erdman (1964). The following plants were
identified from the trapping area on Morfield Ridge:
_Lithospermum ruderale_
_Chenopodium pratericola_
_Achillea millefolium_
_Artemisia tridentata_
_Aster bigelovii_
_Chrysothamnus depressus_
_Chrysothamnus nauseosus_
_Helianthus annuus_
_Helianthella_ sp.
_Lactuca_ sp.
_Lepidium montanum_
_Quercus gambelii_
_Agropyron smithii_
_Bromus inermis_
_Bromus japonicus_
_Oryzopsis hymenoides_
_Calochortus nuttallii_
_Linum perenne_
_Sphaeralcea coccinea_
_Polygonum sawatchense_
_Solidago petradoria_
_Wyethia arizonica_
_Nicotiana attenuata_
_Fendlera rupicola_
_Penstemon linarioides_
Only _Peromyscus maniculatus_, _Perognathus apache_ and _Reithrodontomys
megalotis_ were taken in this area (Table 1). Many birds inhabit this
area, including hawks, ravens, towhees, jays, juncos, woodpeckers,
doves, sparrows and titmice. Rabbits, badgers and mule deer also live in
the area. Only two reptiles, a horned lizard and a collared lizard, were
seen.
_South of Far View Ruins_
Two parallel trap lines were established on October 4, 1961, in the area
immediately south of Far View Ruins (Fig. 1). In altitude, latitude and
geographical configuration the area is similar to that trapped in the
Morfield burn, but the Chapin Mesa site had not been burned.
Canopy vegetation is pinyon-juniper forest. A dense understory was made
up of _Amelanchier utahensis_ (serviceberry), _Cercocarpos montanus_
(mountain mahogany), _Purshia tridentata_ (bitterbrush), and _Quercus
gambelii_ (Gambel oak). The ground cover consisted of small clumps of
_Poa fendleriana_ (muttongrass), and _Koeleria cristata_ (Junegrass),
intermingled with growths of one or more of the following:
_Artemisia nova_
_Solidago petradoria_
_Sitanion hystrix_
_Astragalus scopulorum_
_Lupinus caudatus_
_Eriogonum alatum_
_Penstemon linarioides_
_Eriogonum racemosum_
_Eriogonum umbellatum_
_Polygonum sawatchense_
_Amelanchier utahensis_
_Purshia tridentata_
_Comandra umbellata_
Seeds of _Cercocarpos montanus_ covered the ground under the bushes in
much of the trapping area, and large numbers of juniper berries were on
the ground beneath the trees. Individuals of _P. truei_ and _P.
maniculatus_ were caught in this area (Table 1).
Several deer, rabbits, one coyote, and numerous birds were seen in the
area. No reptiles were noticed, but they were not searched for. A
mountain lion was seen in this general area two weeks after trapping was
completed.
_West of Far View Ruins_
Three pairs of traplines were run west of Far View Ruins in an area
comparable in vegetation, altitude, general topography, and
configuration to the area previously described. The elevations concerned
are typical of the middle parts of mesas throughout the park. This area
differs from the trapping area south of Far View Ruins and the one on
Morfield Ridge in being wider and on the western side of the mesa.
The woody understory was sparse in most places, and where present was
composed of _Cercocarpos montanus_, _Purshia tridentata_, _Fendlera
rupicola_ (fendlerbush), _Amelanchier utahensis_, _Quercus gambelii_,
and _Artemisia tridentata_ (sagebrush). The herbaceous ground cover was
dominated by _Solidago petradoria_ (rock goldenrod), and
grasses--including _Poa fendleriana_, _Oryzopsis hymenoides_, and
_Sitanion hystrix_. Other herbaceous species were as follows:
_Echinocercus coccineus_
_Achillea millefolium_
_Aster bigelovii_
_Wyethia arizonica_
_Lepidium montanum_
_Lupinus caudatus_
_Yucca baccata_
_Linum perenne_
_Eriogonum racemosum_
_Eriogonum umbellatum_
_Polygonum sawatchense_
_Delphinium nelsonii_
_Penstemon linarioides_
Fresh diggings of pocket gophers were observed along the trap lines.
Badger tunnels were noted in numerous surface mounds that are remnants
of prehistoric Indian dwellings, but no badgers were seen. Numerous deer
and several rabbits were present. Juncos, two species of jays, and
woodpeckers were seen daily. No reptiles were observed.
Both _Peromyscus maniculatus_ and _P. truei_ were caught in this area
(Table 1).
_Big Sagebrush Stand, South Chapin Mesa_
A circular trapline, 1,000 feet in circumference, was established on
November 16, 1961, in a stand of big sagebrush, and was operated for 30
consecutive nights.
The vegetation of the trapping area was predominantly _Artemisia
tridentata_ (big sagebrush), interspersed with a few scattered seedlings
of pinyon and juniper. This stand was burned in 1858 (tree-ring date by
David Smith) and some charred juniper snags still stood. The deep sandy
soil also supported a variety of grasses and a few other small plants.
The following species were common in this area:
_Bromus inermis_
_Oryzopsis hymenoides_
_Poa fendleriana_
_Sitanion hystrix_
_Solidago petradoria_
_Orthocarpus purpureo-albus_
The 15 to 20 acres of sagebrush were surrounded by pinyon-juniper
forest. The trapping station closest to the forest was approximately 100
feet from the edge of the woodland. More _P. truei_ than _P.
maniculatus_ were caught here (Table 1).
_East Loop Road, Chapin Mesa_
The trapping area lies north of Cliff Palace, eastward of the loop road,
at elevations of 6,875 to 6,925 feet. Two pairs of traplines were run
from January 9, 1962, to January 12, 1962, and from February 13 to 15,
1962.
Vegetation was pinyon-juniper woodland with an understory of mixed
shrubs. One to four inches of old snow covered the ground during most of
the trapping period, but the ground beneath trees and shrubs was
generally clear, providing suitable location for traps.
Numerous juncos and jays were seen in this area; deer and rabbits also
were present.
Individuals of _P. truei_ and of _P. maniculatus_ were taken (Table 1).
_Navajo Hill, Chapin Mesa_
Navajo Hill is the highest point (8,140 feet) on Chapin Mesa. The top of
the hill is rounded and the sides slope gently southward and westward
until they level out into mesa-top terrain at elevations of 7,950 to
8,000 feet. The northern and eastern slopes of the hill drop abruptly
into the respective canyon slopes of the East Fork of Navajo Canyon and
the West Fork of Little Soda Canyon. The gradually tapering southwestern
slope of the hill extends southward for one mile and is bisected by the
main highway, which runs the length of the mesa top.
Heavy growths of grasses cover the ground; _Amelanchier utahensis_,
_Cercocarpos montanus_, and _Fendlera rupicola_ comprise the only tall
vegetation. Trees are lacking on this part of the mesa, except on the
canyon slopes, where _Quercus gambelii_ forms an almost impenetrable
barrier.
Four traplines were run from May 4-7, 1962, and from May 9-12, 1962. _P.
maniculatus_ was taken but _P. truei_ was not present here in 1962, or
in 1964 or 1965 when additional trapping was performed as a check on
populations (Table 1).
Other species trapped include the montane vole, long-tailed vole, and
Colorado chipmunk. Mule deer and coyotes were abundant in the area.
Striped whipsnakes, rattlesnakes and gopher snakes are known to occur in
this vicinity (Douglas, 1966).
_North End Wetherill Mesa_
In 1934 a widespread fire deforested large areas of pinyon-juniper
woodland on the northern end of Wetherill Mesa. The current vegetation
consists of shrubs with a dense ground cover of grasses. Many dead trees
still remain on the ground, providing additional cover for wildlife.
The trapping area was a wide, grassy meadow, three and a half miles
south of the northern end of the mesa. A pronounced drainage runs
through this area and empties into Rock Canyon. Four traplines were run
parallel to each other. The first lines were established on May 23,
1962, and the second pair on June 3, 1962.
Another pair of lines was run in a grassy area two miles south of the
northern escarpment of Wetherill Mesa. This area was one and a half
miles north of the above-mentioned area. These lines ran along the
eastern side of a drainage leading into Long Canyon. The vegetation was
essentially the same in both areas, and they will be considered
together.
The vegetation was composed predominantly of grasses. _Quercus gambelii_
and _Amelanchier utahensis_ were the codominant shrubs. _Artemisia
tridentata_ and _Chrysothamnus depressus_ (dwarf rabbitbrush), were
common. Plants in the two areas included the following:
_Juniperus scopulorum_
_Symphoricarpos oreophilus_
_Artemisia ludoviciana_
_Sitanion hystrix_
_Stipa comata_
_Astragalus scopulorum_
_Artemisia tridentata_
_Chrysothamnus depressus_
_Helianthus annuus_
_Tetradymia canescens_
_Quercus gambelii_
_Bromus tectorum_
_Poa fendleriana_
_Lupinus caudatus_
_Yucca baccata_
_Sphaeralcea coccinea_
_Eriogonum umbellatum_
_Amelanchier utahensis_
_Fendlera rupicola_
_Lomatium pinatasectum_
Individuals of _P. maniculatus_ and of _Reithrodontomys megalotis_ were
caught (Table 1).
TABLE 1--Major Trapping Localities in Mesa Verde National Park,
Colorado.
Vegetational Key as Follows: 1) Pinyon-Juniper-Muttongrass
2) Pinyon-Juniper-Mixed Shrubs 3) Juniper-Pinyon-Bitterbrush
4) Juniper-Pinyon-Mountain Mahogany 5) Grassland with Mixed Shrubs
6) Big Sagebrush 7) Pinyon-Juniper-Big Sagebrush 8) Grassland.
Column headings:
A: Date
B: No. trap nights
C: _P. truei_
D: _P. man._
E: Type of vegetation
========================+=============+=======+=====+=====+===
Locality | A | B | C | D | E
------------------------+-------------+-------+-----+-----+---
Morfield Ridge | Sept. 1961 | 1080 | 0 | 83 | 5
| Oct. 1963 | 360 | 0 | 13 | 5
| | | | |
S. of Far View | Oct. 1961 | 360 | 10 | 13 | 2
| | | | |
W. of Far View | Oct. 1961 | 1080 | 22 | 17 | 2
| | | | |
South Chapin Mesa | Nov.-Dec. | 3600 | 16 | 9 | 6
| 1961 | | | |
| | | | |
East Loop Road | Jan. 1962 | 720 | 6 | 2 | 2
| | | | |
Navajo Hill | May 1962 | 720 | 0 | 18 | 5
| Aug. 1964 | 20 | 0 | 2 | 5
| Aug. 1965 | 50 | 0 | 8 | 5
| | | | |
N. Wetherill Mesa | May-June | 1080 | 0 | 57 | 5
| 1962 | | | |
| | | | |
Bobcat Canyon Drainage | June 1962 | 360 | 0 | 0 | 6
| | | | |
N. of Long House | June 1962 | 1080 | 3 | 4 | 1
| | | | |
Mug House--Rock Springs | Aug. 1962 | 720 | 8 | 14 | 4
| Aug. 1963 | 720 | 9 | 7 | 4
| | | | |
S. Wetherill Mesa | Aug. 1962 | 720 | 0 | 5 | 3
| | | | |
1 mi. SE Park Entr. | June 1963 | 50 | 0 | 16 | 7
| | | | |
1/4 mi. SE Park Entr. | July 1963 | 100 | 0 | 7 | 8
| | | | |
M-2 Weather Sta. | May 1964 | 25 | 2 | 0 | 1
| | | | |
8 mi. S North Rim | | | | |
Moccasin Mesa | Aug. 1964 | 100 | 0 | 3 | 8
| | | | |
10 mi. S North Rim | | | | |
Moccasin Mesa | Aug. 1964 | 25 | 2 | 0 | 2
------------------------+-------------+-------+-----+-----+---
_Bobcat Canyon Drainage_
Bobcat Canyon, a large secondary canyon on the eastern side of Wetherill
Mesa, is a major drainage for much of the mesa at its widest part. The
mesa top drains southeast into a pour-off at the head of Bobcat Canyon.
A stand of big sagebrush, _Artemisia tridentata_, grows in the sandy
soil of the drainage, and extends northwest for several hundred yards
from the pour-off. The sagebrush invades the pinyon-juniper forest at
the periphery of the area.
Two traplines were set in the drainage, with trapping stations at
intervals of 25 feet. The lines traversed elevations of 7,000 to 7,100
feet, and were run from June 26 to 29, 1962.
Grasses are the most abundant plants in the ground cover. _Artemisia
dracunculus_ is common in the drainage, and _A. nova_ grows around the
periphery of the drainage. Other species occurring in this stand
include:
_Aster bigelovii_
_Tetradymia canescens_
_Tragopogon pratensis_
_Bromus tectorum_
_Poa fendleriana_
_Sitanion hystrix_
_Stipa comata_
_Lupinus argenteus_
_Calochortus gunnisonii_
_Sphaeralcea coccinea_
_Phlox hoodii_
_Eriogonum umbellatum_
_Peraphyllum ramosissimum_
_Purshia tridentata_
_Penstemon linarioides_
No mice were caught in three nights of trapping (360 trap nights), and
only one mammal, a _Spermophilus variegatus_, was seen.
_North of Long House, Wetherill Mesa_
Pinyon-juniper forest with a dominant ground cover of _Poa fendleriana_
was described by Erdman (1962) as one of the three distinct types of
pinyon-juniper woodland on Wetherill Mesa. Such a woodland occurs
adjacent to the Bobcat Canyon drainage, and is continuous across the
Mesa from above Long House to the area near Step House. Plants in the
ground cover include:
_Cryptantha bakeri_
_Opuntia rhodantha_
_Chrysothamnus depressus_
_Solidago petradoria_
_Koeleria cristata_
_Lupinus argenteus_
_Yucca baccata_
_Phlox hoodii_
_Eriogonum racemosum_
_Eriogonum umbellatum_
_Cordylanthus wrightii_
_Pedicularis centranthera_
_Penstemon linarioides_
_Penstemon strictus_
Two traplines were run from July 9 to 12, 1962, in the area south of the
Bobcat Canyon drainage at an elevation of 7,100 feet. No mice were
caught in three nights of trapping. Four additional lines were
established on July 24, 1962, and were run for three nights, in the area
north of the Bobcat Canyon drainage at elevations of 7,100 to 7,150
feet.
_P. maniculatus_ and _P. truei_ were caught here (Table 1). This
vegetational association may have few rodents because there is a
shortage of places where they can hide. Although _Poa fendleriana_ is
abundant, the lack of shrubs leaves little protective cover for mammals.
_Mug House--Rock Springs_
A juniper-pinyon-mountain mahogany association extends from the area of
Mug House to Rock Springs, on Wetherill Mesa. On that part of the ridge
just above Mug House, the understory is predominantly _Cercocarpos
montanus_ (mountain mahogany), but northward toward Rock Springs the
understory changes to _Fendlera rupicola_, _Amelanchier utahensis_,
_Cercocarpos_, and _Purshia tridentata_. The ground cover is essentially
the same as that in the pinyon-juniper-muttongrass association described
previously.
Four traplines were run from July 31 to August 2, 1962, and from August
13 to 15, 1963. These lines ran northwest-southeast, starting 1,000 feet
southeast of, and ending 3,000 feet northwest of, Mug House. The lines
traversed elevations of 7,225 to 7,325 feet. Individuals of _P.
maniculatus_ and _P. truei_ were caught here (Table 1).
Deer and rabbits inhabit the trapping area. Bobcats have been seen, by
myself and by others, near Rock Springs. Lizards of the genera
_Cnemidophorus_ and _Sceloporus_, as well as gopher snakes were seen in
this area.
_Juniper--Pinyon--Bitterbrush_
Three pairs of traplines were run from August 7-9, 1962, in a
juniper-pinyon-bitterbrush stand on the southern end of Wetherill Mesa,
starting 200 yards southwest of Double House (Fig. 1).
The forest on the southern end of the mesas consists of widely-spaced
trees, which reflect the low amounts of precipitation at these lower
elevations. Juniper trees are more numerous than pinyons, and both
species are stunted in comparison to trees farther north on the mesa.
_Purshia tridentata_ (bitterbrush) is the understory codominant.
_Artemisia nova_ (black sagebrush) is present and grasses are the most
abundant plants in the ground cover. Herbaceous species in the sparse
ground cover include the following:
_Opuntia polyacantha_
_Solidago petradoria_
_Lathyrus pauciflorus_
_Penstemon linarioides_
_Lupinus caudatus_
_Yucca baccata_
_Phlox hoodii_
Only _P. maniculatus_ was caught in this stand; all mice were caught in
the first night of trapping.
Five areas were selected for trapping in the summers of 1963 or 1964, in
order to test hypotheses concerning habitat preferences of each of the
species of _Peromyscus_. Four of these areas appeared to be ideal
habitat for one species, but not for the other. The fifth area was
expected to produce both species of _Peromyscus_. Each of these areas is
discussed below.
_One Mile Southeast of Park's Entrance_
A small stand of _Artemisia tridentata_, occurring one mile southeast of
the entrance to the park, is bordered to the north and northeast by a
grassy meadow, discussed in the following account. Kangaroo rats have
been reported in this general area, and I wanted to determine whether
_P. maniculatus_ and _Dipodomys_ occurred together there. Fifty trap
nights in this sagebrush, on June 20, 1963, yielded only _P.
maniculatus_ (Table 1).
_Meadow, One-Quarter Mile Southeast of Park's Entrance_
A grassy meadow lies just to the east of the highway into the park,
one-quarter of a mile southeast of the park's entrance. On July 30,
1963, one hundred traps were placed in two lines through the meadow, and
were run for one night. Only individuals of _P. maniculatus_ were caught
(Table 1).
_M-2 Weather Station, Chapin Mesa_
The M-2 weather station of the Wetherill Mesa Archeological Project was
on the middle of Chapin Mesa at an elevation of 7,200 feet. This site
was in an old C. C. C. area, about one mile north of the park's U. S.
Weather Bureau station. The vegetation surrounding the M-2 site was a
pinyon-juniper-muttongrass association. It was thought that both species
of _Peromyscus_ would occur in this habitat.
On May 10, 1964, 25 traps were placed in this area and were run for one
night. Only individuals of _P. truei_ were caught (Table 1).
_Grassy Meadow, Southern End Moccasin Mesa_
This large meadow is located eight miles south of the northern rim of
Moccasin Mesa. The meadow lies in a broad, shallow depression that forms
the head of a large drainage (Fig. 1). To the south of the meadow the
drainage deepens, then reaches bedrock as it approaches the pour-off.
On August 23, 1964, one hundred traps were set in pairs in a line
through the middle of the meadow; adjacent pairs were 20 feet from each
other. Only individuals of _P. maniculatus_ were caught (Table 1).
Grasses are dominant in the ground cover, and _Sphaeralcea coccinea_
(globe mallow) is codominant. The abundance of globe mallow is due to
the present and past disturbance of this meadow by a colony of pocket
gophers. Trees are absent in the meadow. Species of plants include the
following:
_Opuntia polyacantha_
_Chenopodium_ sp.
_Artemisia ludoviciana_
_Chrysothamnus nauseosus_
_Koeleria cristata_
_Poa pratensis_
_Lupinus ammophilus_
_Calochortus gunnisonii_
_Erigeron speciosus_
_Gutierrezia sarothrae_
_Tetradymia canescens_
_Tragopogon pratensis_
_Bromus tectorum_
_Sphaeralcea coccinea_
_Eriogonum racemosum_
_Polygonum sawatchense_
_Comandra umbellata_
_Penstemon strictus_
_Bedrock Outcroppings, Southern End Moccasin Mesa_
Two miles south of the preceding site, much of the mesa is a wide
expanse of exposed bedrock, which extends approximately 100 feet inward
from the edges of the mesa. Pinyon-juniper-mixed shrub woodland adjoins
the bedrock.
On August 23, 1964, 25 traps were placed along the bedrock, near the
edge of the forest. Only two mice, both _P. truei_, were caught. (Table
1).
HOME RANGE
In order to learn how extensively mice of different ages travel within
their habitats, whether their home ranges overlap, and how many animals
live within an area, it was necessary to determine home ranges for as
many mice, of each species, as possible (Hayne, 1949; Mohr and Stumpf,
1966; Sanderson, 1966).
In 1961, the Colorado Department of Fish, Game and Parks established a
permanent trapping grid in the area south of Far View Ruins (Fig. 1). The
grid was constructed and used by Mr. Harold R. Shepherd, Senior Game
Biologist, and his assistant, in the summers of 1961 and 1962, in a
study concerning the effect of rodents on browse plants used by deer.
The Department of Fish, Game and Parks allowed me to use the grid during
1963 and 1964, and also permitted me to use its Sherman live traps.
The grid is divided into 16 units, each with 28 stations (Fig. 2). Traps
at four stations (1a, 1b, 1c, 1d) are operated in each unit at the same
time, with two traps being set at each station. The traps are moved each
day in a counter-clockwise rotation to the next block of four stations
(2a, 2b, 2c, 2d) within each unit. The stations are arranged so that on
any given night, traps in adjacent units are separated by at least 200
feet. As a result, animals are less inclined to become addicted to
traps, for even within one unit they must move at least 50 feet to be
caught on consecutive nights.
[Illustration: FIG. 2: Diagram of trapping grid for small mammals,
showing units of subdivision. Trapping stations were numbered
in each unit as shown in unit A.]
Traps were carefully shaded and a ball of kapok was placed in each trap
to provide protection against the killing temperatures that can develop
inside. In spite of these precautions, mice occasionally succumbed from
heat or cold. The traps were baited with coarsely-ground scratch feed.
Mammals trapped in the grid were inspected for molt, sexual maturity,
larvae of botflies, anomalies, and other pertinent data. Each animal was
marked by toe- and ear-clipping and then released. Four toes were used
on each front foot, and all five toes were used on each hind foot; two
toes were clipped on the right front foot to signify number nine. The
tip of the left ear was clipped to signify number 100, and the tip of
the right ear was clipped to signify 200. If 300 or more animals had
been captured, the tip of the tail would have been clipped to represent
number 300. A maximum of 799 animals could have been marked with this
system, which was used by Shepherd. I continued with it, starting my
listings with number one.
Only two mice were caught that had been marked in the previous season by
Shepherd.
Live traps were operated in the trapping grid from July 9 through
October 25, 1963, and from June 25 through August 21, 1964. Traps were
rotated through all stations five different times (35 days) in 1963, and
twice (14 days) in 1964. Approximately three man hours were required
each day to service and rotate the traps to the next group of stations.
By the autumn of 1964, a total of 282 mice had been captured, marked and
released; these were handled 817 times. In 1963, 235 mice were caught
for an average of 20 captures per day; in 1964, 47 mice were caught for
an average of 9 captures per day.
Calculations of Home Range
A diagrammatic map of the trapping grid was drawn to scale with one
centimeter equal to 100 linear feet. Trapping stations were numbered on
the diagram to correspond with stations in the field. An outline of this
drawing also was prepared to the same scale, but station numbers were
omitted. Mimeographed copies of such a form could be placed over the
diagrammatic map and marks made at each station where an animal was
caught. A separate form was kept for each animal that was caught four or
more times.
In calculating home range, it was assumed that animals would venture
half-way from the peripheral stations, at which they were caught, to the
next station outside the range. A circle having a scaled radius of 25
feet (half the distance between stations) was inscribed around each
station on the periphery of the home range by means of a drafting
compass. The estimated range for each animal was then outlined on the
form by connecting peripheries of the circles. Both the inclusive
boundary-strip method and the exclusive boundary-strip method (Stickel,
1954:3) were used to estimate the ranges. The area encompassed within
the home ranges was measured by planimetering the outline of the
drawing. At least two such readings were taken for each home range; then
these planimeter values were converted into square feet.
The customary practice in delimiting home ranges on a scaled map of a
grid is to inscribe squares around the peripheral stations at which the
animal was trapped, and then to connect the exterior corners of these
squares (Stickel, 1954:3). If the distance between stations was 50 feet,
such squares would have sides 50 feet long. An easier method is to
inscribe a circle having a scaled radius of 25 feet around the
peripheral stations by means of a drafting compass. To my knowledge this
method has not been used previously and consequently has not been tested
by experiments with artificial populations.
To test the accuracy of this method, a "grid of traps" was constructed
by using 8-1/2 by 11 inch sheets of graph paper with heavy lines each
centimeter. The intersects of the heavier lines were considered as trap
stations. A "home range" of circular shape, 200 feet (4 cm.) in
diameter, with an area of 31,146 square feet (0.71 acre), was cut from a
sheet of transparent plastic. Another "home range" was made in an oblong
shape with rounded ends. This range measured 2 by 65 centimeters (100 by
325 feet) and had an area of 32,102 square feet (0.74 acre). Each
plastic range was tossed at random on sheets of graph paper for fifty
trials each. The range was outlined on the graph paper, then circles
having a scaled radius of 25 feet were inscribed around each "trap
station" within the range. The peripheries of the inscribed circles were
then connected and the estimated home range was delimited by the
exclusive boundary-strip method. The estimated range was measured by
planimetering, and the data were compared with the known home range
(Table 2).
It was found that when calculated by the exclusive boundary-strip
method, the circular home range was overestimated by 2.22 per cent. The
oblong home range was overestimated by only 1.50 per cent. Stickel
(1954:4) has shown that the exclusive boundary-strip method is the most
accurate of several methods of estimating home ranges, and in her
experiments this method gave an overestimate of two per cent of the
known range. Thus, my method of encircling the peripheral stations
yields results that are, on the average, as accurate as the more
involved method of inscribing squares about the trap stations, and saves
a great deal of time as well. My method probably yields better accuracy;
a perfect circle is easily drawn by means of a compass, whereas a
perfect square is more difficult to construct without a template.
It is generally understood that the estimated home range of an animal
tends to increase in size with each additional capture; this increase is
rapid at first, then slows. Theoretically, the more often an animal is
captured, the more reliable is the estimate of its home range. Most
animals, however, rarely are captured more than a few times. The
investigator must decide how many captures are necessary before the data
seem to be valid for estimating home ranges.
An animal must be trapped at a minimum of three stations before its home
range can be estimated, and even then the area enclosed in the triangle
will be much less than the actual home range. Some investigators have
plotted home ranges from only three captures (Redman and Selander,
1958:391), whereas others consider that far more captures are needed to
make a valid estimate of range (Stickel, 1954:5).
TABLE 2--Summary of Data from Experiments in Calculating Home Ranges
for an Artificial Population.
=======+========+=========+==========+========+================+========
| | | | Actual | Calculated |
| No. | Trap | Shape | area | area of range |
Series | of | spacing | of | of | by exclusive | +- S. D.
| trials | in ft. | range | range | boundary-strip |
| | | | in ft. | method |
-------+--------+---------+----------+--------+----------------+--------
A | 50 | 50 | Circular | 31,146 | 31,782 | 9,600
B | 50 | 50 | Oblong | 32,102 | 32,583 | 9,466
-------+--------+---------+----------+--------+----------------+--------
In my study, 161 individuals of _P. truei_ were caught from one to 13
times each. The estimated home ranges of 10 individuals of _P. truei_,
each caught from eight to 13 times, were plotted and measured after each
capture from the fourth to the last. The percentage of the total
estimated range represented by the fourth through tenth captures was,
respectively, 52, 65, 73, 85, 88, 93, and 96 per cent.
Ninety-seven individuals of _P. maniculatus_ were caught from one to 10
times each. For five individuals that were each caught from seven to 10
times, the percentage of total estimated range represented by the fourth
through seventh captures was, respectively, 59, 69, 85, and 93 per cent.
The above percentages do not imply that the true home range of
individuals of these species can be reliably estimated after seven or 10
captures; the average percentages do, however, indicate a fairly rapid
increase in known size of home ranges between the fourth and tenth
captures. The estimated home ranges of _P. maniculatus_ tended to reach
maximum known size at about seven captures, whereas the estimated ranges
of _P. truei_ tended to attain maximum known size after nine or more
captures. The controversy over the number of captures of an individual
animal required for a reliable estimate of its home range was not
settled by my data.
I initially decided to estimate home ranges for animals caught five or
more times and at three or more stations. Of the 282 animals caught and
marked, only 48 were caught five or more times. Because of the small
numbers of _P. maniculatus_ that were caught five or more times, I
wanted to determine whether mice caught four times had an estimated
range that was significantly smaller than that of mice caught five
times. Eight individuals of _P. maniculatus_ were caught four times
each, and it seemed desirable to use the data from these mice if such
use was justified. Data from the 48 mice caught five or more times were
used for this testing.
By means of a T-test, I compared the estimated ranges of those 48 mice
following their fourth capture with ranges estimated after the fifth
capture. The results did not demonstrate significant differences between
the two sets of estimates; therefore, I decided to use data resulting
from four or more captures, and at three or more stations.
Table 3 shows estimations of the home ranges of males and females of
each species of _Peromyscus_. When the inclusive boundary-strip method
is used, the area encompassed by the range tends to be larger than the
area of the same range when estimated by the exclusive boundary-strip
method. Stickel (1954:4) has shown that the inclusive boundary-strip
method overestimates the home range by about 17 percent.
Analysis of Home Range by Inclusive Boundary-Strip Method
When all age groups were considered, the ranges of 16 males of _P.
truei_ averaged 20,000 to 80,000 square feet (ave. 47,333; S. D.
19,286). The sizes of home ranges were not significantly different (P >
0.05) between adult and subadult (including juveniles and young) males.
All females of _P. truei_ (22) had ranges encompassing 16,666 to 83,333
square feet (ave. 40,666; S. D. 17,566). Sizes of home ranges between
adult and non-adult females did not differ significantly. The mean range
of adult males of _P. truei_ did not differ from that of adult females
(P > 0.05).
Fifteen males of _P. maniculatus_ had ranges of 16,666 to 66,666 square
feet (ave. 34,222; S. D. 16,000); six adult males had ranges of 33,333
to 53,333 square feet (ave. 38,666). Sizes of home ranges of adult and
non-adult males of this species did not differ significantly.