Occasional papers

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Occasional Papers

Tulane University

Museum of Natural History

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Mammals of the Riparian Region of the Colorado
River in the Grand Canyon Area of Arizona

Royal D. Suttkus

Glenn H. Clemmer

Clyde Jones

Occasional Papers is published by Tulane University, Museum of Natural His-
tory. The Occasional Papers is dedicated primarily to Natural History: Sys-
tematics, Environmental Biology and Biogeography. The Occasional Papers will
appear irregularly in consecutively numbered issues. For information and policy
on exchanges, write to: Royal D. Suttkus, Director

Museum of Natural History

Tulane University

Belle Chasse, Louisiana 70037

When citing this publication, authors are requested to use the following: Occas.
Pap. Tulane U. Mus. Nat. Hist.

Cover Photo: "Shadows in the Night, Tracks in the Sand."

Jeanne Suttkus

The National Fish and Wildlife Laboratory, Washington, D.C, supported pub-
lication of this number.

This number is dedicated to Jeanne Suttkus.
Printed by Drake Printers, Tuscaloosa, Alabama.

Mammals of the Riparian Region of the Colorado
River in the Grand Canyon Area of Arizona

Royal D. Suttkus

Glenn H. Clemmer

Clyde Jones

ABSTRACT

Information assembled during field activities carried out periodically from
September 1970 to September 1976 is summarized for 31 species of mammals that
occur in the riparian region along the Colorado River in the Grand Canyon.
Some recent changes in the habitats of mammals in the area are discussed, and
some influences of these habitat changes on the distribution and abundance
of mammals are summarized.

Editorial Committee for This Paper

Dr. Michael A. Bogan
National Fish and Wildlife Laboratory
U.S. Fish and Wildlife Service
National Museum of Natural History
Washington, D.C. 20560

Dr. Donald F. Hoffmeister
Museum of Natural History
University of Illinois
Urbana, Illinois 61801

Dr. Don E. Wilson

National Fish and Wildlife Laboratory
U.S. Fish and Wildlife Service
National Museum of Natural History
Washington, D.C. 20560

NUMBER 2, 1978

Mammals of the Riparian Region of the Colorado
River in the Grand Canyon Area of Arizona1

Royal D. Suttkus

Tulane University, Museum of Natural History

Belle Chasse, Louisiana 70037

Glenn H. Clemmer

Department of Biological Sciences, Mississippi State University
Mississippi State, Mississippi 39762

Clyde Jones
National Fish and Wildlife Laboratory

U.S. Fish and Wildlife Service

National Museum of Natural History

Washington, D.C. 20560

Introduction

Studies of mammals along the Colorado River in the
bottom of the Grand Canyon have been carried out in-
frequently during the past century. The early interests
and corresponding field activities in this area by the
Bureau of Biological Survey were summarized in the
reports by Merriam (1890), Bailey (1935), and Goldman
(1937). General information on the distribution of mam-
mals in the area was provided by Hall and Kelson
(1959), Cockrum (1960, 1964), and Hoffmeister and Dur-
ham (1971). Hoffmeister (1971) presented a comprehen-
sive review of the mammals in the Grand Canyon Na-
tional Park. Some recent distributional information was
provided by Ruffner and Carothers (1975). Ruffner and
Tomko (1976) studied demographic characteristics and
diets of some rodents at about four localities in this
geographic area.

In recent years increasing concerns about a wide array
of management practices in arid lands in general and
the Colorado River in the Grand Canyon in particular
have created new demands for knowledge of wildlife
resources and habitats in these areas. Some examples of
concerns and controversies about environmental manage-
ment of the Colorado River within the Grand Canyon
were given by Dolan et al. (1974, 1977) and Eiseman
(1978).

The purposes of this report are to provide some basic
information on the mammals that occur along the Colo-
rado River in the Grand Canyon and to identify loca-
tions of materials and related information for use by
biologists and others working on natural history prob-
lems in this geographic area.

'Contribution Number 16, Tulane University, Museum of Natural
History.

Methods and Materials

Fifteen float trips on the Colorado River were made
from September 1970 to September 1976. Six float trips
(September 1970, August 1971, July 1972, May and
August 1973, May 1974) were made with commercial
river runner companies. Float trips and some other
studies on the river in cooperation with the National
Park Service were carried out in April, June, July, and
September 1975, and in May, June, and September 1976.

In addition to specific work on mammals, the purposes
of these expeditions were to gather information on fishes,
reptiles, amphibians, vegetation, and other aspects of
the habitats of the area. Some of the data on fishes of
the Colorado River within the Grand Canyon have been
published elsewhere (Suttkus and Clemmer, 1977).

Specimens of mammals, consisting of study skins,
skulls, skeletons, and some embryos, were obtained from
41 locations (Figure 1) within the study area (see the list
of localities). These localities coincided with camp sites
used during river trips; mammals were collected as time
allowed. Ten localities were chosen for major emphasis
and were studied systematically during the late phases
of our studies of mammals. The major study sites were
selected either because of heavy use by the visitors on
the river or the unique faunas and habitats that occur
there, as well as to avoid duplication of effort by other
researchers in the area. Sight records and signs of mam-
mals were recorded whenever they were observed. Mam-
mals were collected during both the night and day. Most
mammals were trapped, a few were netted, and some
were shot. Museum specials and rat traps were placed
about 10 m apart in transect lines before dusk, checked
at least twice during the night, and picked up after
dawn. Traps were set occasionally at sites where signs of
mammals were observed. Traps were baited with either

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

rolled oats or peanut butter or a mixture of both. Mist
nets for bats were set over water, across ravines, over
trails, over openings between rocks, and among vegeta-
tion. Nets were maintained normally for 3 to 4 hrs.
after dusk. All specimens of mammals were prepared in
the field. Specimens, field notes, catalogues, photographs,
and related information are deposited at the Museum
of Natural History, Tulane University, and the National
Fish and Wildlife Laboratory, National Museum of
Natural History. Specimens examined are listed in the
accounts for each species.

The study area includes both banks of the Colorado
River from Lee's Ferry, Coconino County, Arizona, to
Sand Point, Mohave County, Arizona. This part of the
Colorado River extends for 294.5 miles from just below
the Utah-Arizona border to the south shore of Mead
Reservior near the Nevada-Arizona state line. All of the
area studied is within the Arizona climatic pattern, which
is a regime with winter precipitation, spring drought,
summer precipitation, and fall drought (Lowe, 1964).
The upper part of the study area is in the Navahonian
biotic province, and the lower portion is included in the
Mohavian biotic province (Lowe, 1964).

The riparian vegetation along the Colorado River is
described and illustrated by Dolan et al. (1977). Vegeta-
tion on the river banks and at the mouths of tributaries
includes Pluchea sericca, Tamarix pentandra, Sahx
exigua, Baccharis glutinosa, Baccharis sergiloides, and
Brickellia atractyloides; high beaches and dunes support
Pluchea sericca, Bromus rubens, Alhagi camelorum,
Salsola kali, and Dicoria brandegei; upper slopes and
terraces have stands of Fallugia paradoxia, Acacia greggii,
Prosopis juliflora, Encelia frutescens, and Baccharis
sarothroides. McDougall (1964) described and provided
keys for 975 kinds of plants from the Grand Canyon
National Park, and he indicated those found within the
Grand Canyon. Some additional comments, maps, and
photographs of the riparian vegetation and desert scrub
of the inner gorge were provided by Hoffmeister (1971).
A summary of the flora for part of the bottom of the
Grand Canyon was presented by Theroux (1976).

In the following list of localities, brief descriptions are
provided for the major study areas. The numbers of
species of mammals and the total numbers of specimens
obtained are provided for the 10 major study sites. The
distances down the river for all localities were taken
from Lee's Ferry, river mile 0, in accordance with the
Belknap (1975), Grand Canyon River Guide. Numbers
preceding localities are those used in Figure 1.
1. Lee's Ferry, river mile 0, right bank (Figure 2). 9
species, 95 specimens.

The gentle lower slopes of the area are mostly of the
Moenkopi formation; these slopes are dissected by
arroyos. The top of the Kaibab limestone is apparent on
the down river side of this area. Lee's Ferry is the start-
ing point for boat traffic through the Grand Canyon,
and there is a large camping facility; this area receives
very heavy human use. In addition, there is a long history
of human habitation at this site. Desert scrub vegetation

is dominant in the area, but there are thick stands of
Tamarix along the Colorado River, especially near the
boat launching site and near the mouth of the Paria
River. According to Rusho and Crampton (1975), Thales
Haskell noted in his diary in 1859 that grass and cotton-
wood trees were present near the mouth of the Paria
River; these authors included a photograph of the Lee's
Ferry Ranch in which there is a large cottonwood tree
in the foreground. There are no large cottonwood trees
in the area at the present time. A few cottonwood sap-
lings occur near the mouth of the Paria River, but these
trees are cut down regularly by beavers.

2. 3.9 miles N Marble Canyon, river mile 2, right bank.

3. House Rock, river mile 17, right bank.

4. River mile 19, left bank (Figure 3). 9 species, 44
specimens.

This site is at the base of the Supai formation. The
talus slope is narrow and steep. On the upriver side,
there is a small ravine between the cliff and the sand-
bar at the base. The mouth of the ravine is flooded
frequently, and supports a dense growth of sedges in the
bottom and Tamarix on the sides. This area receives
frequent, but mostly short term, visits by river tourists.

5. River mile 22, left bank.

6. River mile 26, left bank.

7. Stanton Cave, river mile 31.8, right bank.

8. Buck Farm Canyon, river mile 41, right bank
(Figures 4, 5). 11 species, 157 specimens.

An extensive deltaic fan of sand and boulders (Figure
4) from Buck Farm Canyon abuts against the steep slope
of the Muav limestone, which in turn slopes up to the
base of the vertical Redwall limestone. A ravine extends
along the base of the cliff on the downriver side of the
canyon to a marshy area at the junction with the Colo-
rado River (Figure 5). Some very large mesquite trees
are on the deltaic side of the ravine. Sedges, grasses, and
thick clumps of Tamarix vegetate the wet area at the
mouth of the ravine. This area is used frequently as a
campsite by river parties.
9. President Harding Rapid, river mile 44, left bank.

10. Little Nankoweap, river mile 50, right bank.

11. Kwagunt Creek, river mile 56, right bank.

12. Kwagunt Rapid, river mile 56.5, left bank.

13. Lava Canyon, river mile 65.5, left bank.

14. Cardenas Creek, river mile 71, left bank.

15. Unkar Rapid, river mile 72, right bank (Figure 6).
7 species, 88 specimens.

A small beach with a steep sandy area in back extends
up against a steep slope of Dox sandstone of the Grand
Canyon Series. The upper slope has very sparse vegeta-
tion, but clumps of Tamarix are found on the sandy
areas. This area receives some use by campers, and is
visited frequently for short stops by river runners.

16. Boucher Creek, river mile 96.5, left bank (Figure 7).
7 species, 33 specimens.

The jagged Vishnu schist and Zoroaster granite walls
are only a short distance from the river at this study
site. There is a narrow sandy area between the walls and
the river; on the upriver side this joins the small boulder

NUMBER 2, 1978

strewn fan of Boucher Creek, a small flowing tributary
of the Colorado River, and on the downriver side the
schist and granite form a vertical wall at the edge of the
river. Tamarix is the dominant vegetation on the sandy
strip; typical desert scrub occurs in Boucher Creek Can-
yon. This area is used frequently as a campsite by river
travelers.

17. Crystal Creek, river mile 98.2, right bank.

18. Tuna Creek, river mile 99.3, left bank.

19. Lower Bass Camp, river mile 108.5, right bank
(Figure 8). 8 species, 58 specimens.

This study site is a sandy beach with a high jutting
mass of Vishnu schist on the down river side. The Lower
Grand Canyon Series is exposed above the Upper Granite
Gorge formation. There are numerous dense clusters of
Tamarix scattered over the beach area. This area re-
ceives heavy use by humans.

20. River mile 112, right bank.

21. River mile 114, right bank.

22. Elves Chasm, river mile 1 1G, left bank.

23. River mile 1 19.5, left bank.

24. River mile 124, left bank.

25. Stone Creek, river mile 132, right bank.

26. Deer Creek Falls, river mile 136.2, left bank
(Figure 9). 6 species, 54 specimens.

This study site is directly across the Colorado River
from Deer Creek Falls. There is a small sandy area sur-
rounded by slopes composed of Vishnu schist and Zoro-
aster granite. Much of the lower surface is either buried
or littered with debris from the formations above. The
Tapeats sandstone forms a cliff above the schist and
granite. This area is used as a campsite and for short
stops by people on the river. There is a small stand
ol Tamarix at the edge of the river, with desert send)
on the surrounding slopes. There is a considerable
amount of grass on a protected slope on the downriver
side of this locality.

27. Overhang, river mile 137, left bank.

28. Fishtail Canyon, river mile 139, right bank.

29. River mile 151.5, right bank.

30. Tuckup Canyon, river mile 164.5, right bank
(Figure 10). 6 species, 35 specimens.

This is a steep walled canyon with a small narrow
deltaic fan along the nearly vertical wall of the Muav,
Devonian, and Redwall limestones. Underlying beds
of Bright Angel shale are exposed at river level just
below the study area. Desert scrub vegetation prevails
where there is adequate substrate; there is very little
Tamarix in this area. This place is used as a campsite by
river parties.

31. National Canyon, river mile 166.5, left bank.

32. Fern Glen Canyon, river mile 168, right bank.

33. Mohawk Canyon, river mile 171.5, left bank.

34. Lava Falls Rapid, river mile 182, right bank.

35. Whitmore Wash, river mile 188, right bank.

36. Riser mile 196, left bank.

37. River mile 212.5, left bank.

38. 220 Mile Canyon, river mile 220, right bank.

39. Bridge Canyon dam site, river mile 238, left bank
(Figure II). 5 species, 94 specimens.

The steep jagged slope of the Lower Granite Gorge
extends down to the river and surrounds a small sandy
area. There are a few scattered clumps of Tamarix near
the river, with sparse vegetation, mostly mesquite and
barrel cactus, on the slopes. This area is heavily utilized
by people from the river parties and from boat traffic
on Mead Reservoir.

40. Scorpion Island, river mile 279.5, left bank (Figures
12, 13). 7 species, 63 specimens.

This study site is outside of the Grand Wash Cliffs
on the south side of Mead Reservoir. The area is a flat
terrace of sand and gravels, with an abrupt concave slope
down to the water (Figure 12). A few types of desert scrub
vegetation, including creosote bushes, are widely spaced
over the terrace (Figure 13). Tamarix is established along
the shore line. This area is visited frequently by people.
II. Sand Point, river mile 294.5, left bank.

Results and Discussion

Hoffmeister (1971) listed 74 species ol mammals for
the Grand Canyon National Park; lour species (Lfrsus
horribilis, Cams lupus, Felis onca, Antilocapra ameri-
cana) have been extirpated from the area. Rulfner and
Carothers (1975) added two more species for the Park,
one native and one introduced. Of the 72 species cur-
rently known from the Park, 27 were found in the bottom
of the Grand Canyon along the Colorado River. In
addition, four more species were encountered along the
Colorado River in the upper parts of Mead Reservoir.
We examined 1,053 specimens for this study.

Myotis californicus

This species was taken at six localities along the upper
portion of the river. Most animals weie captured in
mist nets stretched across arroyos near walls of the can-
yon. Two bats were caught as they flew about lights in a
campground. One animal was shot as it Hew above a
sandy beach. Hoffmeister (1971) considered this the
most common Myotis within the Grand Canyon.

Animals with single embryos were captured on 31
May 1976, 1; 1 [line 1976, 4 and 3 June 1976, 1. Mea-
surements of crown-rump lengths of embryos ranged
from 4.1 to 8.7 mm (x = 6.60 mm).

Specimens examined. 12.— Coconino County: Lee's
Ferry, river mile 0, right bank. 2; Rivei mile 19. left
bank. 2; Rivet mile 26, left bank, 1; Buck Farm Canyon,
river mile 41, right bank, 5; Boucher Creek, river mile
96.5, left bank, I; River mile 112. right hank. I.

Myotis thysanodes

A single specimen of the hinged myotis was caught
in a mist net set across a small arroyo near its junction
with the Colorado River. The arroyo contained stands
of Tamarix along the sicks. Numerous bats were seen
flying and feedine about these shrubs. The fringed

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

myotis has not been reported from the bottom of the
Grand Canyon (Hoffmeister, 1971).

Specimens examined, 1.— Coconino County: River mile
19, left bank. 1.

Myotis yumanensis

Specimens of the Yuma myotis were obtained at one
locality in the canyon and on the south shore of Mead
Reservoir. Cockrum (1960) listed materials from Jacobs
Pools and Supai Canyon. Hoffmeister (1971) reported
that these bats were common at Phantom Ranch and in
Havasu Canyon. At Buck Farm Canyon, animals were
captured in mist nets set across an arroyo near a sheer
rock wall and across a passage between boulders. The
latter area was used as a night roost by numerous bats.

Twelve females captured on 1 June 1976 each carried
a single embryo. Crown-rump lengths of the embryos
ranged from 3.5 to 10.1 mm (x = 5.05 mm).

Specimens examined, 16.— Coconino County: Buck
Farm Canyon, river mile 41, right bank, 15. Mohave
County: Sand Point, river mile 294.5, left bank, 1.

Pipistrellus hesperus

We obtained specimens of the western pipistrelle at
seven localities along the Colorado River. Hoffmeister
(1971) plotted three localities on the river for this species.
All of the specimens reported herein were shot as they
foraged either in the mouths of side canyons or over
beaches. We agree with Hoffmeister (1971) that these
are the most common bats in the Grand Canyon, es-
pecially along the lower portions of the river. These
animals were observed frequently during the middle of
the day while flying over the river, especially in narrow
parts of the canyon.

Two specimens shot on 3 June 1976 each contained a
small embryo. The embryos were not measured.

Specimens examined. 25.— Coconino County: River
mile 50, right bank, 3: Boucher Creek, river mile 96.5,
left bank, 2: Lower Bass Camp, river mile 108.5, right
bank, 3; Deer Creek Falls, river mile 136.2, left bank,
9; Overhang, river mile 137, left bank, 3. Mohave County:
Scorpion Island, river mile 279.5, left bank, 4: Sand
Point, river mile 291.5, left bank, 1.

Plecotus townsendii

The western big eared bat was not reported from
within the rims of the Grand Canyon by Hoffmeister
(1971). However, Ruffner and Carothers (1975) reported
five females taken from Stanton Cave on 6-7 June 1970
and 11 July 1972. We obtained specimens of P. town-
sendii at six places along the river. Animals were caught
in mist nets plated either between stands of Tamarix
or between steep rock walls in narrow gorges. On 2 Sep-
tember 1976 several hundreds of these bats were found
roosting during the day in Stanton Cave. Whether P.
toninseiidii is a resident of this cave is not known, but
this seems likely since Ruffner and Carothers (1975) re-

ported two females with embryos. Remains of Eptesicus
and Myotis were reported by Euler (1978) from archeo-
logical and paleobiological investigations at Stanton
Cave. The colony of P. townsendii in Stanton Cave is
apparently the largest assemblage of bats of this species
that has been located in recent years. For a review of
colony sizes of this species, see the report by Humphrey
and Kunz (1976).

One female captured on 31 May 1976 contained an
embryo that had a crown-rump length of 9.8 mm.

Specimens examined, 12.— Coconino County: River
mile 19, left bank, 2; Stanton Cave, river mile 31.8, right
bank, 5; Buck Farm Canyon, river mile 41, right bank,
1; Unkar Rapid, river mile 72, right bank, 2; Lower
Bass Camp, river mile 108.5, right bank, 1. Mohave
County: Tuckup Canyon, river mile 164.5, right bank, 1.

Antrozous pallidus

Pallid bats were found at two localities along the upper
portion of the river. The animals were captured in mist
nets, one as it flew around lights in a campground and
the others as they flew among Tamarix trees in an
arroyo. Hoffmeister (1971) plotted a single locality on
the Colorado River for this species, but noted the com-
mon occurrence of these animals in the Grand Canyon.

Specimens examined, 3.— Coconino County: Lee's
Ferrv, river mile 0, right bank, 1; River mile 19, left
bank, 2.

Tadarida brasiliensis

One specimen of the free-tailed bat was shot during
this study. Hoffmeister (1971) postulated that T. brasil-
iensis probably occurred in many areas in the bottom
of the canyon. Although these bats usually colonize caves,
we found no evidence of the species in Stanton Cave. Bat
Cave, river mile 266, right bank, which was mined for
guano at one time, contained no bats when we visited
there on 8 September 1976. However, the presence of
some fairly fresh fecal material indicated that some bats
still use this cave.

Specimens examined, L— Coconino County: Lower
Bass Camp, river mile 108.5, right bank, 1.

Lepus californicus

This species was seen in the vicinity of Lee's Ferry and
at Scorpion Island. Because of its preference for open
country, these are the only suitable places for this species
in the areas studied.

Specimens examined, 0.

Ammospermophilus harrisii

This species was recorded at a single locality near the
south shore of Mead Reservoir. This taxon has not been
reported from within the Grand Canyon (Hoffmeister,
1971). For some information about the distribution of
A. harrisii along the east side of the lower Colorado
River, see the work bv Cockrum (1960).

NUMBER 2, 1978

Specimens examined, 3.— Mohave County: Scorpion
Island, river mile 279.5, left bank, 3.

Ammospermophilus leucurus

A small series of specimens of this species was ob-
tained at the upper end of the study area, where these
animals were abundant and active in late summer. There
is little published information available about the oc-
currence and distribution of this form along the river
and in the bottom of the Grand Canyon (Cockrum, I960,
Hoffmeister, 1971). On 2 September 1976 we saw at
close range an A. leucurus among rocks on a small sandy
beach at river mile 24, right bank, but we were not able
to collect a voucher specimen. Ruffner and Carothers
(1975) mentioned sightings of this form along the river
but listed no specimens.

Specimens examined, 75.— Coconino County: Lee's
Ferry, river mile 0, right bank, 75.

Spermophilus variegatus

We collected specimens of the rock squirrel at three
localities in the canyon. According to Cockrum (1960)
and Hoffmeister (1971), this species occurs along the
Colorado River above the Nevada-Arizona state line.
We saw S. variegatus frequently as they sat on the tops
of rocks during the early hours of the day. Rock squirrels
were especially common in the vicinity of Phantom
Ranch.

Specimens examined, 4.— Coconino County: House
Rock, river mile 17, right bank, 1; River mile 19, left
bank, 2; Elves Chasm, river mile 116, I.

Perognathus amplus

We obtained specimens of the Arizona pocket mouse
only on Scorpion Island where it was the least common
rodent trapped. The current distribution and status of
this species in the vicinity of the Mead Reservoir seems
unclear. A series of specimens of P. amplus was collected
near Pierce Ferry, Arizona, in 1942 (Cockrum, 1960).
This species has not been recorded from within the
Grand Canyon (Hoffmeister, 1971).

Specimens examined, 2.— Mohave County: Scorpion
Island, river mile 279.5, left bank, 2.

Perognathus formosus

We found the long-tailed pocket mouse along the
north side of the Colorado River at six localities in the
upper portions of the canyon. As anticipated by Hoff-
meister (1971), the distribution of this species in the
bottom of the Grand Canyon is considerably more ex-
tensive than thought previously (see the distribution
maps by Cockrum, 1960, and Hall and Kelson, 1959).
This Perognathus was especially abundant in the vicinity
of Unkar Rapid, river mile 72, right bank. Animals were
trapped mostly along an interface between a rocky slope
and sand dunes. The rocky slope had little vegetation;
the dunes supported considerable Tamarix pentandra
and Prosopis juliflora and some sparse grasses.

Specimens examined, 29.— Coconino County: Lee's
Ferry, river mile 0, right bank, 1; 3.9 miles N Marble
Canyon, river mile 2, right bank, 1; Buck Farm Canyon,
river mile 41, right bank, 3; Little Nankoweap, river
mile 50, right bank, 3; Unkar Rapid, river mile 72, right
bank, 20; Fishtail Canyon, river mile 139, right bank, 1.

Perognathus intermedius

Specimens of the rock pocket mouse were trapped at
18 localities along the left bank of the Colorado River.
All of our records are downriver from the junction of
the Little Colorado River. Cockrum (1960) and Hoff-
meister (1971) summarized previous records of this
species from the Grand Canyon and the lower Colorado
River. Habitat preferences of these mice were discussed
by Hoffmeister (1971). These animals seemed especially
common at the Bridge Canyon dam site, river mile 238,
left bank, where they were trapped mostly on sandy
substrata strewn with rocks near the bases of cliffs and
on steep rocky slopes.

Specimens examined, 91.— Coconino County: Lava
Canyon, river mile 65, left bank, 2; Cardenas Creek,
river mile 71, left bank, 1; Boucher Creek, river mile
96.5, left bank, 6; River mile 119.5, left bank, 1; Deer
Creek Falls, river mile 136.2, left bank, 11; Overhang,
river mile 137, left bank, 7; National Canyon, river mile
166.5, left bank, 1; Mohawk Canyon, river mile 171.5,
left bank, 1; River mile 196, left bank, 3. Mohave County:
Bridge Canyon dam site, river mile 238, left bank,
51; Scorpion Island, river mile 279.5, left bank, 6; Sand
Point, river mile 294.5, left bank, 1.

Dipodomys merriami

We found this species at two localities on the lower
parts of the river. On Scorpion Island, river mile 279.5,
left bank, this kangaroo rat was the most frequently
trapped mammal. This form was not reported from the
Grand Canyon National Park by Hoffmeister (1971), who
discussed some reasons why kangaroo rats probably do
not occur in the canyon.

Two pregnant animals were trapped on 8 June 1976.
One contained three embryos that measured 25.9, 26.9,
and 27.1 mm; one had two embryos that were 19.5 and
21.7 mm in crown-rump length.

Specimens examined, 46.— Mohave County: Scorpion
Island, river mile 279.5, left bank, 43; Sand Point, river
mile 294,5, left bank, 3.

Castor canadensis

No beavers were collected during this study. Tracks
and signs of feeding by beavers were seen at several
places along the river. There was a beaver lodge along
the right bank of the Colorado River just below the
boat launching area at Lee's Ferry. On 21 May 1977 a
beaver in the river 3 to 8 m from the lodge was observed
for about 20 minutes. A bank den was seen on the lower
part of the Paria River near its confluence with the

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

Colorado River. On several occasions while seining fishes
at night in the mouth of the Paria River, we heard
beavers slapping the water with their tails. Other bank
dens and lodges were seen along the river, and many
signs of these animals were recorded in the vicinity of
Fern Glen Canyon, river mile 168. For information on
the historical and current distribution, as well as the
status of C. canadensis along the Colorado River, see the
maps and discussions by Cockrum (1960) and Hoff-
meister (1971).

Specimens examined, 0.

Reithrodontomys megalotis

We obtained specimens of this species at one locality;
Hoffmeister (1971) cited two localities in the bottom of
the canyon for the western harvest mouse. Our specimens
were trapped in a rather mesic area with grasses and
willows. Considerable efforts were made to trap these
mice during subsequent stops in the area, but without
success.

Specimens examined, 3.— Coconino County: Buck
Farm Canyon, river mile 41, right bank, 3.

Peromyscus boylii

The brush mouse was obtained at eight localities in
the study area. Although P. boylii occurs throughout the
Grand Canyon National Park, few were previously
recorded from along the Colorado River (Hoffmeister,
1971). Brush mice were not common at any of the
localities where we encountered them.

An animal captured on 1 June 1976 contained three
embryos that measured 8.4, 8.5, and 8.8 mm, crown-rump
length. A female taken on 4 June 1975 contained five
embryos that were 12.3, 13.0, 13.1, 13.2, and 13.3 mm,
crown-rump length.

Specimens examined, 20.— Coconino County: Lee's
Ferry, river mile 0, right bank, 1; River mile 19, left
bank. 3: Buck Farm Canyon, river mile 41, right bank,
7; Little Nankoweap, river mile 50, right bank, 2; Unkar
Rapid, river mile 72, right bank, 4: Boucher Creek,
river mile 96.5, left bank, 1. Mohave County: Tuckup
Canyon, river mile 164.5, right bank, 1: Fern Glen
Canyon, river mile 168, right bank, I.

Peromyscus crinitus

We obtained specimens of the canyon mouse at 22
sites along the Colorado River. We agree with Hoff-
meister (1971), who stated that this species was found
frequently in barren rocky places, especially canyon
walls. This was the most abundant Peromyscus at Buck
Farm Canyon, river mile 41, right bank; the animals
were scampering over our luggage and sleeping bags
most of the night. These mice were trapped among
clumps of grasses and rocks on the broad deltaic fan
at the mouth of the canyon (Figure 4). Hoffmeister
(1971) correlated the distribution of this species with the
presence of seed producing plants on rocky slopes in the

Grand Canyon. In addition, he mentioned some possible
effects of food materials supplied by humans on the
distribution and abundance of this species in the vicinity
of Phantom Ranch. The canyon mouse was abundant at
House Rock, river mile 17, right bank, in September
1970. A sheltered area beneath an overhanging ledge
was a popular campsite until the ledge broke off and
occluded most of the high beach area. There was a pro-
nounced scarcity of canyon mice when we made a return
visit to this site during 1975, which was more than
two years after the rock fall.

A pregnant female was obtained on 4 June 1975. The
embryos measured 22.1, 22.9, and 23.3 mm in crown-
rump length.

Specimens examined, 210.— Coconino County: House
Rock, river mile 17, right bank, 6; River mile 19, left
bank, 6; River mile 22, left bank, 5: Buck Farm Canvon,
river mile 41, right bank, 80; Little Nankoweap, river
mile 50, right bank, 4; Kwagunt Creek, river mile 56,
right bank, 2; Unkar Rapid, river mile 72, right bank,
7; Boucher Creek, river mile 96.5, left bank, 5: Crystal
Creek, river mile 98.2, right bank, 1; Lower Bass Camp,
river mile 108.5, right bank, 21; River mile 114, right
bank, 4; Stone Creek, river mile 132, right bank, 3;
Deer Creek Falls, river mile 136.2, left bank, 8; Over-
hang, river mile 137, left bank, 8; Fishtail Canyon, river
mile 139, right bank, 1; River mile 151.5, right bank, 2.
Mohave County: Tuckup Canyon, river mile 164.5, right
bank. 14; Fern Glen Canyon, river mile 168. right bank,
17; Lava Falls Rapid, river mile 182, right bank, 3;
Whitmore Wash, river mile 188, right bank, 4; 220 Mile
Canyon, river mile 220, right bank, 5; Bridge Canyon
dam site, river mile 238, left bank, 4.

Peromyscus eremicus

Merriam (1890) described this species as the most
abundant mammal found in the Grand Canyon during
his work there. According to Hoffmeister (1971), "Cactus
mice are the principal white-footed mouse inhabitants
of the inner parts of the canyon, except for the rocky
walls where canyon mice live." The cactus mouse was
the most cosmopolitan Peromyscus that we encountered
during our work along the Colorado River; this species
was recorded from 34 localities. We were impressed by
the abundance of these mice at our campsite at Fern
Glen Canyon, river mile 168, right bank, on the night
of 6 September 1976. While eating dinner, we fed these
mice bits of food from our plates.

The number of embryos in pregnant females ranged
from one to five (Table 1). Two pregnant females, taken
on 2 June 1976 and 30 July 1975, had the gray juvenile
pelage: these mice had embryos that were much smaller
than those from other females taken at the same time.

Specimens examined, 387— Coconino County: Lee's
Ferry, river mile 0, right bank, 5; River mile 19, left
bank. 25; River mile 22, left bank, 14; River mile 26,
left bank, 2; Buck Farm Canyon, river mile 41, right
bank, 32; President Harding Rapid, river mile 44, left

NUMBER 2, 1978

bank, 2; Little Nankoweap, river mile 50, right bank,
7; Kwagunt Creek, river mile 56, right bank, 6; Kwagiint
Rapid, river mile 56.5, left bank, 12; Lava Canyon, river
mile 65.5, left bank, 14; Cardenas Creek, river mile 71,
left bank, 4; Unkar Rapid, river mile 72, right bank, 49;
Boucher Creek, river mile 96.5, left bank, 13; Crystal
Creek, river mile 98-2, right bank, 2; Tuna Creek, river
mile 99.3, left bank, 5; Lower Bass Camp, river mile
108.5, right bank, 20; River mile 114, right bank, 5;
River mile 119.5, left bank, 6; River mile 124, left bank,
2; Stone Creek, river mile 132, right bank, 5; Deer
Creek Falls, river mile 136.2, left bank 19; Overhang,
river mile 137, left bank, 20; Fishtail Canyon, river mile
139, right bank, 3. Mohave County: Tuckup Canyon,
river mile 164.5, right bank, 17; National Canyon, river
mile 166.5, left bank, 6; Fern Glen Canyon, river mile
168, right bank, 34; Mohawk Canyon, river mile 171.5,
left bank, 4; Lava Falls Rapid, river mile 182, right bank,
7; Whitmore Wash, river mile 188, right bank, 6; River
mile 196, left bank, 4; River mile 212.5, left bank,
2; 220 Mile Canyon, river mile 220, right bank, 5; Bridge
Canyon dam site, river mile 238, left bank, 20; Scorpion
Island, river mile 279.5, left bank, 4; Sand Point, river
mile 294.5, left bank, 6.

Peromyscus maniculatus

The deer mouse was collected at five localities along
the upper parts of the Colorado River in the Grand
Canyon. Hoffmeister (1971) examined specimens of this
species from three localities along the river, and re-
ported that these mice were especially uncommon in
the bottom of the canyon. Ruffner and Carothers (1975)
referred to two additional localities (River mile 122,
right bank, River mile 274, right bank). At Lee's Ferry,
river mile 0, right bank, this species seemed almost as
common as other Peromyscus, but elsewhere P. mani-
culatus was trapped much less frequently than most of
the other members of the genus.

Specimens examined, 13.— Coconino County: Lee's
Ferry, river mile 0, right bank, 7; Buck Farm Canyon,
river mile 41, right bank, 1; Lava Canyon, river mile
65.5, left bank, 2; Unkar Rapid, river mile 72, right
bank, 1; Boucher Creek, river mile 96.5, left bank, 2.

Neotoma albigula

The white-throated wood rat was found at only two
localities during this study. There are few records for
N. albigula in the bottom of the Grand Canyon (Hoff-
meister, 1971).

Specimens examined, 2.— Coconino County: Lava
Canyon, river mile 65.5, left bank, 1; Cardenas Creek,
river mile 71, left bank, 1.

Neotoma lepida

This species was taken at 28 localities along both sides
of the river throughout the study area. Desert wood
rats seemed common everywhere; piles of nest materials
and droppings, as well as animals, were seen at nearly
every place that we spent time. These animals were es-
pecially abundant at the Bridge Canyon dam site, river
mile 238, left bank. Based on trapping results and ob-
servations of signs, this species seems most abundant in
rocky habitats, but animals were also trapped on sandy
beaches.

Specimens examined, 87.— Coconino County: Lee's
Ferry, river mile 0, right bank, 2; River mile 19, left
bank, 1; River mile 22, left bank, 3; Buck Farm Canyon,
river mile 41, right bank, 9; Little Nankoweap, river
mile 50, right bank, 3; Kwagunt Creek, river mile 56,
right bank, 2; Kwagunt Rapid, river mile 56.5, left bank,
1; Lava Canyon, river mile 65.5, left bank, 1; Unkar
Rapid, river mile 72, right bank, 5; Boucher Creek,
river mile 96.5, left bank, 3; Crystal Creek, river mile
98.2, right bank, 2; Tuna Creek, river mile 99.3, left
bank, 2; Lower Bass Camp, river mile 108.5, right bank,
10; River mile 112, right bank, 1; River mile 114, right
bank, 1; River mile 119.5, left bank, 2; River mile 124,
left bank, 1; Deer Creek Falls, river mile 136.2, left
bank, 6; Overhang, river mile 137, ieft bank, 1; Fishtail
Canyon, river mile 139, right bank, 1. Mohave County:
Tuckup Canyon, river mile 164.5, right bank, 1; Fern
Glen Canyon, river mile 168, right bank, 3; Mohawk
Canyon, river mile 171.5, left bank, 2; Whitmore Wash,
river mile 188, right bank, 1; River mile 196, left bank,
2; Bridge Canyon dam site, river mile 238, left bank,
19; Scorpion Island, river mile 279.5, left bank, 1; Sand
Point, river mile 294.5, left bank, 1.

Peromyscus truei

We obtained this species at three localities along the
river. The pinon mouse was not previously reported with-
in the inner gorge along the Colorado River (Hoff-
meister, 1971).

A female captured on 4 May 1976 contained three
embryos that measured 17.1, 17.8, and 19.9 mm in crown-
rump length.

Specimens examined, 3.— Coconino County: Lee's
Ferry, river mile 0, right bank, 1; Buck Farm Canyon,
river mile 41, right bank, 1. Mohave County: Tuckup
Canyon, river mile 164.5, right bank, 1.

Canis latrans

A coyote was observed along the shore of Mead Reser-
voir at River mile 277, right bank, on 8 June 1976.
Hoffmeister (1971) stated that this species occurred
throughout the Grand Canyon National Park, but was
more abundant above the inner gorge.

Specimens examined, 0.

Urocyon cinereoargenteus

The gray fox was observed at Lee's Ferry, river mile
0, right bank, on 30 May 1976 and at River mile 51, right
bank, on 21 September 1975. Animals were seen in the
ravines between the campground and the Colorado River

8

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

at Lee's Ferry. According to Hoffmeister (1971), the
gray fox occurs throughout the Grand Canyon National
Park.

Specimens examined, 0.

Bassariscus astutus

Specimens of this species were obtained from two
localities during this study. Hoffmeister (1971) reported
specimens from Phantom Ranch, and commented
on the common occurrence of the ringtail in the
Grand Canyon. Tracks of B. astutus were noted
at nearly every site where we stopped along the
river. On 4 September 1976 at Lower Bass Camp,
river mile 108.5, right bank, we saw at least four different
animals between 1830 and 2030 hrs. One animal passed
through the middle of our camp and removed some speci-
mens of rodents that were pinned to a drying tray.
While we were camped at Overhang, river mile 137,
left bank, for the night of 5 September 1976, we watched
at least eight individual ringtails. The animals moved
about along the Tapeats sandstone ledges of a cliff,
and usually remained from about 3 to 10 m above the
ground. Sometimes we saw as many as four animals at
a time within the beam from a hand held lamp. Their
vocalizations were heard several times during the night.

Specimens examined, 3.— Coconino County: Lower
Bass Camp, river mile 108.5, right bank, 1; Overhang,
river mile 137, left bank, 2.

Spilogale gracilis

"Spotted skunks are the commonest carnivores within
the canyon . . ." (Hoffmeister, 1971). We obtained spe-
cimens at four localities and observed either animals or
their signs elsewhere along the river. On 5 September
1976, while working at Overhang, river mile 137, left
bank, we saw S. gracilis run along the base of the cliff,
enter a pile of rocks, and emerge with a Peromyscus;
this occurred on two occasions between 2200 and 2400
hrs. On this particular night, we frequently saw spotted
skunks and ringtails at the same time on the lower
ledges of the cliff. Two animals were caught by hand,
one as it emerged from a hole in a rock pile, and the
other as it attempted to take a rodent from a pre-
parator.

Specimens examined, 4.— Coconino County: Lower
Bass Camp, river mile 108.5, right bank, 1: Deer Creek
Falls, river mile 136.2, left bank, 1; Overhang, river mile
137, left bank, 2.

Equus asinus

Feral burros are common in some parts of the canyon
and along the Colorado River. For a concise summary of
the history of this species in the Grand Canyon, see the
account by Hoffmeister (1971). Distribution of feral
burros on the south side of the Colorado River was
depicted by Berger (1977). We saw a group of six animals
near the water at River mile 185 on the right bank. Evi-
dence of the presence of burros was most apparent from

the area around Lower Bass Camp, river mile 108.5,
to the Bridge Canyon dam site, river mile 238. During
our study a total of 14 sightings of burros was recorded
from the right side of the Colorado River from River
mile 208 to River mile 220.
Specimens examined, 0.

Dama hemionus

Mule deer are present in limited numbers in the can-
yon throughout the year, and they sometimes congregate
in certain places near the river during the winter (Hoff-
meister, 1971). Our observations of this species were
recorded as follows: River mile 36.5, right bank, 1; River
mile 50, right bank, 2; River mile 51.5, left bank, 1;
River mile 54, right bank, 2; River mile 57.5, left bank,
2; River mile 58.7, left bank 1.

Specimens examined, 0.

Ovis canadensis

This species ranges throughout the Grand Canyon, but
it is apparently more common on the south side of the
river than on the north side (Hoffmeister, 1971). Berger
(1977) mapped some localities for the occurrence of
O. canadensis on the south side of the Colorado River,
and reported that these sheep use the river as a primary
source of water during the spring and summer, but they
migrate to other elevations during the rest of the year.
We saw bighorn sheep at the following places: River
mile 105.5, left bank, 5; River mile 116, left bank, 1;
River mile 126.7, left bank, 3; River mile 152, right
bank, 1; River mile 165, left bank, 1; River mile 185,
right bank, 1; River mile 202, left bank, 4; River mile
206, left bank, 1; River mile 215, left bank, 7.

Specimens examined, 1.— Coconino County: Tuna
Creek, river mile 99.3, left bank, 1.

Habitats for mammals along the Colorado River with-
in the area studied have changed considerably in recent
years. For example, see the description above of the
vegetation in the vicinity of Lee's Ferry. Numerous pro-
gressive habitat changes are related to the closure of Glen
Canyon Dam in 1963, the subsequent fluctuations in
water levels of the river, and the corresponding changes
in the erosion and deposition of sediments along the
river. In addition, heavy recreational use of the river
and the available beaches impacts the habitats near the
water. An excellent review of vegetational changes along
the Colorado River is provided by Karpiscak (1976). His
discussions of vegetational changes are documented by
paired photographs, including pre-dam and contempor-
ary habitat pictures. The general trends of the geomor-
phological changes along the Colorado River are sum-
marized by Dolan et al. (1974, 1977), who indicated that
the rates of degradation at many sites exceeds the capa-
city of the natural processes to reestablish natural land-
scapes. The changes in habitats along the Colorado River
influence the distribution and abundance of mammals in
the area.

NUMBER 2, 1978

No evidence of the occurrence of Lutra canadensis was
obtained during this study. Hoffmeister (1971) sum-
marized reports of the presence of the river otter in and
along the Colorado River, and commented on the availa-
bility of food for this species. Since the closure of the
Glen Canyon Dam, the persistent cold temperature and
fluctuating water levels in the river, as well as other
factors, have contributed to a rather depleted fish fauna
in the Colorado River (Suttkus and Clemmer, 1977).
There may be inadequate food resources to maintain
river otters in this area.

The widespread incorporation of human debris into
the sediment matrices at numerous beaches to form a
"sand-box condition" is described in detail by Dolan
el al. (1977). Small food particles, which constitute a
large portion of the debris left in these areas by humans,
may be an important factor contributing to the use of
certain sites by mammals for foraging. Although it is
difficult to quantify, we were impressed constantly by
the presence and abundance of mammals in our camp
areas at night. Hoffmeister (1971) mentioned only
briefly some possible influences of food materials pro-
vided by humans on wild mammals in the vicinity of
Phantom Ranch.

In the early phases of this investigation, studies of
mammals were carried out at Sand Point, river mile
294.5, left bank. Large releases of water from Powell
Reservoir were stored in the Mead Reservoir, and this
study site and surrounding habitats were destroyed by
inundation with several meters of water.

The area adjacent to the Colorado River in the Grand
Canyon is an intriguing and challenging place for con-
ducting studies of mammals. Because of the lack of
knowledge about the details of distribution, status, and
ecological relationships of mammals, the constantly oc-
curring changes in habitats and the impacts of human
activities, and the increasing environmental concerns for
the region, a considerable amount of biological in-
vestigation remains to be carried out along the Colo-
rado River in the Grand Canyon.
Acknowledgments

We owe our thanks to Jeanne Suttkus for providing
the original stimulus to study the fauna and flora in
the Grand Canyon. After attending a meeting of the
Sierra Club in the spring of 1970, Jeanne made the
following announcement: "I don't know what you are
going to do this summer, but I am going to float down
the Colorado River." Numerous people helped us in
many ways throughout this study. We especially thank
Lyn Branch, Steve Carothers, Sherrill Clemmer, Cindy
Deacon, James Deacon, Maxine Deacon, Robert Esher,
Robert Fisher, Gail Kohl, Linda Loetterle, Patricia Moss,
Dawn Remington, George Ruffner, C. Robert Shoop,
Mark Stevens, and James Williams for helping us collect
and prepare specimens. Michael Bogan identified some
specimens of Myotis. The photographs were taken and
processed by Jeanne Suttkus. Personnel of the National
Park Service and the Museum of Northern Arizona pro-
vided various kinds of logistic support; we appreciate

their tolerances of the numerous stops and delays that
we caused during the float trips. This study was support-
ed in part by a contract (CX92 1060006) from the Na-
tional Park Service to the senior author.

Literature Cited

Bailey, V. 1935. Mammals of the Grand Canyon region. Grand
Canyon Nat. Hist. Assoc, Nat. Hist. Bull. 1:1-42.

Belknap, B. 1975. Grand Canyon river guide. Westwater Books,
Boulder City, Nevada. 6Ui Printing. 51 pp. Not numbered.

Berger, J. 1977. Sympatric and allopatric relationships among
desert bighorn sheep and feral equids in Grand Canyon. South-
west. Nat. 22:540-543.

Cockrum, E. 1960. The Recent mammals of Arizona: Their tax-
onomy and distribution. Univ. Arizona Press, Tucson, viii - 276
pp.

Cockrum, E. 1964. An annotated check list of the Recent mammals
of Arizona. Pp. 249-259 in The vertebrates of Arizona, Lowe, C.
(ed.), Univ. Arizona Press, Tucson, vii + 259 pp.

Dolan, R., A. Howard, and A. Gallenson. 1974. Man's impact on
the Colorado River in the Grand Canyon. American Scientist
62:392-401.

Dolan, R., B. Hayden, A. Howard, and R. Johnson. 1977. Environ-
mental management of the Colorado River within the Grand
Canyon. Environmental Management 1:391-400.

Eiseman, F. 1978. Who runs the Grand Canyon? Natural History
87:82-93.

Euler, R. 1978. Archeological and paleobiological studies at
Stanton's Cave, Grand Canyon National Park, Arizona — A report
of progress. Pp. 141-162 in National Geographic Society research
reports 1969. Oehser, P., and J. Lea (eds.), National Geographic
Society, Washington, x + 658 pp.

Goldman, E. 1937. The Colorado River as a barrier in mammalian
distribution. Jour. Mamm. 18:427-435.

Hall. E.. and K. Kelson. 1959. The mammals of North America.
Ronald Press Company, New York. 2 Vols. 1241 pp.

Hoffmeister, D. 1971. Mammals of Grand Canyon. Univ. Illinois
Press, Urbana. 183 pp.

Hoffmeister, D., and F. Durham. 1971. Mammals of the Arizona
strip including Grand Canyon National Monument. Museum of
Northern Arizona Technical Series No. 11.

Humphrey, S., and T. Kunz. 1976. Ecology of a Pleistocene relict,
the western big-eared bat (Plecotus townsendii), in the southern
Great Plains, Jour. Mamm. 57:470-494.

Karpiscak, M. 1976. Vegetational changes along the Colorado
River. Pp. 1-48 in An ecological survey of the riparian zone of
the Colorado River between Lee's Ferry and the Grand Wash
Cliffs, Arizona, Carothers, S.. and S. Aitchison (eds.), Final
Research Report, Contract No. CX8215O0OO7, National Park
Service, xii + 268 pp.

Lowe, C. 1964. Arizona landscapes and habitats. Pp. 1-132 in The
vertebrates of Arizona, Lowe, C. (ed.), Univ. Arizona Press,
Tucson, vii + 259 pp.

McDougall, W. 1964. Grand Canyon wild flowers. Museum of
Northern Arizona Bull. No. 43, in cooperation with Grand
Canyon Nat. Hist. Assoc, ix + 259 pp.

Merriam, C. 1890. Results of a biological survey of the San
Francisco Mountain region and desert of the Little Colorado,
Arizona. North American Fauna 3: vii-1 36.

Ruffner, G., and S. Carothers. 1975. Recent notes on the distribu-
tion of some mammals of the Grand Canyon region. Plateau

47:154-160.

10

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

Ruffner, G., and D. Tomko. 1976. Mammals of the Colorado River.

Pp. 74-126 in An ecological survey of the riparian zone of the

Colorado River between Lee's Ferry and the Grand Wash Cliffs.

Arizona, Carothers. S.. and S. Aitchison (eds.), Final Research

Report, Contract No CX82150OO07, National Park Service, xii +

268 pp.
Rusho, W., and C. Crampton. 1975. Desert river crossing, historic

Lee's Ferry on the Colorado River. Peregrine Smith, Inc., Salt

Lake City. 126 pp.

Suttkus, R.. and G. Clemmer. 1977. The humpback chub, Gila
cypha, in the Grand Canyon area of the Colorado River. Occas.
Pap. Tulane U. Mus. Nat. Hist. 1:1-30.

Theroux, M. 1976. Vascular flora of the Grand Canyon. Pp. 49-51
in An ecological survey of the riparian zone of the Colorado River
between Lee's Ferry and the Grand Wash Cliffs, Arizona,
Carothers, S., and S. Aitchison (eds.), Final Research Report,
Contract No. CX821500007, National Park Service, xii + 268 pp.

Table I. Reproduction of Peromyscus eremicus obtained during this study. The numbers in-
clude the ranges and the means of the embryos per adult and the ranges and means
of the measurements (mm) of embryos.

Date

Adult

Embryo

Crown-rump length

20 May

1974

22 May

1974

2 jun

1976

30 Jul

1975

3 Aug

1975

24 Sep

1975

2

1-4

(2.50)

19.0-19.2 (19.10)

1

4

16.9-17.2 (17.05)

2

1-3

(2.00)

11.7-23.7 (19.42)

3

3-5

(3.66)

7.8-22.0 (16.28)

1

3

17.9-19.8 (18.73)

1

2

13.4-13.7 (13.55)

NUMBER 2, 1978

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TULANE UNIVERSITY MUSEUM NATURAL HISTORY

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