ecological study of the texas kangaroo rat

7

ECOLOGICAL STUDY OF THE TEXAS KANGAROO RAT

DIPODOMYS ELATOR

by

JIMMY DOSS ROBERTS, B.S.E.

A THESIS

IN

ZOOLOGY

Submltted to the Graduate Faculty of Texas Technological College

in Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accepted

August, 1969

7>o^ T3

(iof>' -'^

ACKNOWLEDGMENTS

I am deeply indebted to Dr. Robert L. Packard for

his direction of this thesis and to my wife for her en-

couragement and assistance.

n

TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

LIST OF TABLES iv

LIST OF ILLUSTRATIONS vi

CHAPTER

I. INTRODUCTION 1

II. MATERIALS AND METHODS 2

III. FINDINGS AND INTERPRETATIONS 15

IV. SUMMARY AND CONCLUSIONS 53

LITERATURE CITED 54

iii

LIST OF TABLES

TABLE

1. Summary of data obtained from live-trapping

four areas 16

2. Trap ranges of female Dipodomys elator 24

3. Trap ranges of male Dipodomys elator 26 4. Percentage of Dipodomys elator captured per

trapping effort on Grid 1 27

5. Percentage of Dipodomys elator captured per trapping effort on Grid II 27

6. Percentage of Dipodomys elator captured per trapping effort on Grid III. 28

7. Percentage of Dipodomys elator captured per trapping effort on Grid IV.... 28

8. Population of Dipodomys elator as estimated by Lincoln Index 30

9. Percentage of Perognathus merriami captured per trapping effort on Grid 1 40

10. Percentage of Perognathus merriami captured per trapping effort on Grid II 40

11. Percentage of Perognathus merriami captured per trapping effort on Grid III 41

12. Percentage of Perognathus merriami captured per trapping effort on Grid IV : 41

13. Percentage of Perognathus hispidus captured per trapping effort on Grid 1 42

14. Percentage of Perognathus hispidus captured per trapping effort on Grid lí 42

15. Percentage of Perognathus hispidus captured per trapping effort on Grid III 43

iv

List of Tables (continued)

16. Percentage of Perognathus hispidus captured per trapping effort on Grid IV 43

17. Record of nighttime observations of Dipodomys el ator 49

.IC

LIST OF ILLUSTRATIONS

FIGURE

1. Vegetational cover map of Grid 1 3

2. Variations of trapping areas on Grid 1 5

3. Vegetational cover map of Grid II 7

4. Vegetational cover map of Grid III 10

5. Vegetational cover map of Grid IV 12

6. Habitat of Dipodomys elator on Grid III 19

7. Open and plugged burrow openings of Dipodomys elator 21

8. Relative abundance and activity of species on Grid 1 32

9. Relative abundance and activity of species on Grid II 34

10. Relative abundance and activity of species on Grid III 36

11. Relative abundance and activity of species

on Grid IV 38

12. Dipodomys elator dusting and scratching area 46

13. Tracks and open burrow of Dipodomys elator in snow 50

vi

CHAPTER I

INTRODUCTION

The Texas kangaroo rat, Dipodomys eiator Merriam, has an ex-

tremely restricted geographic range, occuring in north-central Texas

in Clay, Wichita, Baylor, Wilbarger, Archer, and Foard counties. In

Oklahoma, D. elator was reported from Comanche County (Bailey, 1905);

a questionable record (see Dalquest, 1964, and Blair, 1954) has been

reported in Texas from Coryall County.

Published reports of D. elator are confined either to the re-

cording of sites of capture (Merriam, 1894; Bailey, 1905; Blair,

1949; Blair, 1954; Hedeen, 1953; Dalquest, 1968; Packard and Judd,

1968) or brief notes on the systematics (Grinnell, 1921; Davis, 1942;

Setzer, 1949; Lidicker, 1960). With the exception of cursory ob-

servations (Dalquest and Collier, 1964), no detailed ecological study

0"̂ 2i. elator has been made.

The purposes of this study were to determine: (1) types of

habitat; (2) trap range; (3) approximate population density;

(4) associated species of rodents; (5) predatorial species.

1

CHAPTER II

MATERIALS AND METHODS

Live-traps of the type described by Fitch (1950) were used.

This type of trap captured D. elator more effectively than snap traps

or Sherman live-traps. Traps were baited with either a chopped grain

mixture (milo, corn, and oats) or oatmeal. The chopped grain mix-

ture proved most successful and was used most of the time on the

areas of study. Non-absorbant cotton was used for nesting material

in the traps to reduce mortality in damp weather. Traps were set

25 feet apart in a grid. Four different areas known to be inhabited

^y 5JL e^ator were trapped.

Four variations of grid arrangements were used on one of the

areas (Grid I, see Figs. 1 and 2) located four miles northwest of .

lowa Park, Wichita County, Texas (now a part of the eastern edge of

Buffalo Creek Reservoir). Subarea I (1.37 acres) was trapped Decem-

ber 30, 1965, to January 3, 1966; subarea II (1.55 acres) was trapped

February 7, 1966, to March 11, 1966; subarea III (1.55 acres) was

trapped March 30, 1966, to Oune 12, 1966; and subarea IV (1.43 acres)

was trapped June 21, 1966 to August 1, 1966.

The second area covered .717 acre and possessed a man-made

terrace row in an abandoned field approximately one-half mile northwest

of Grid I (Grid II, see Fig. 3). A creek separated these two grid

sites. All burrov/s of D. elator on this grid were located in the

terrace itself. Two parallel rows of traps were placed 25 feet apart

on each side of the terrace with no traps set on the terrace. Grid II

S i W t <• npr

iimiiL ^ SJ- 'i'l M iÆt

FIGURE 1

Vegetational cover map of Grid I

O CP - mesquite trees - dense grass cover

- low area (standinq water after rain)

- boundaries of dirt road

- trap site

•• = 2 5 feet

FIGURE 2

Variations of trapping areas on Grid I

Subarea I

Subarea II

Subarea III

Subarea IV

• • k • '

•F 1

1

• •

• « • • • • • • • # • • . • « • • • • • • • • • • • • • • • • •

4 • • •

• • • . • • • • • • • • • • • • • • • • « • • • • • * • • • • •

»

5

"n 1

1

J

FIGURE 3

Vegetational cover map of Grid II

O^ - mesquite trees

- dense grass cover

- boundaries of terrace

row

- trap site

^ = 2 5 feet

•Ø''

8

Oc^ iO

c^

C'

'0 '

o> .0

Q

had little grass cover. A few mesquite trees (Prosopis glandulosa

Torrey) were located south of the terrace, but no burrov/s were found

there.

Grid III, comprising 1.43 acres approximately one-half mile

northwest of Grid II, was on land that sloped gently from east to

v/est with scattered mesquite trees. Dense grass was located near

a small water reservoir at the western edge of the grid. This marked

the boundary of the apparent activity of the kangaroo rats. This

grid consisted of ten rows of ten traps each (see Fig. 4).

The fourth area (Grid IV, see Fig. 5) was located on the Goetze

farm approximately seven miles northwest of lowa Park, Texas. The

area occupies 1.43 acres in a pasture approximately 200 yards from

a dwelling. The area had sparse grass cover, and scattered mesquite

trees were present.

All D. elator live-trapped on all four areas were toe-clipped,

weighed, sexed, and released. Males were checked for extended scrotal

sacs, and females were checked for crusty vaginal areas to indicate

breeding condition. Other kinds of rodents were toe-clipped and re-

leased. Residents were determined using McCarley's (1958) method

(a resident is a mouse captured two or more times, but if captured

only twice, at least one capture must be in a nonperimeter trap site).

Live-traps were set for a total of 1476 trap-nights in ten

different areas solely to determine the presence or absence of

D. elator. These areas v/ere located in Wiohita, Wilbarger, and Foard

counties. Most trapping was done near little-used dirt roads in

FIGURE 4

Vegetational cover map of Grid III

O CP

.

1 1

- mesquite trees

- dense grass cover

- boundaries of dirt road

- trap site

< = 25 feet

FIGURE 5

Vegetational cover map of Grid IV

- mesquite trees

- dense grass cover

- boundaries of abandoned dirt road

- trap site

* = 25 feet

O CP

.

y 1

í' -

13

Oo n .0\

0 oa o Q

CP-CP

•Oû (? a

' ^ ;

^

• o

4

o

• ^ , o o

l íu 1111111111111111111

i i i i m i i i i i i i i i m i í i ' n i i í r i í í i M i i i i

:« I I ' I I I I 1 I ' I I I I ' I I I I 1

lllllllllllllllllll

i í t | i i | í i i i i r " i! 11 11

I lî! lllllll!

1

14

areas sparsely vegetated. Live-trapping was supplemented by nighttime

driving to locate and observe D. elator.

Habitat occupied by D. elator was characterized by sparse

vegetation and proved unique enough to permit visual recognition. A

large part of the northwestern portion of Wichita County was surveyed

for the presence of suitable habitat for D. elator. Because much of

this area is inaccessible by road, a small motorcycle was used to

make this survey.

IhMilri..

iiiiii

CHAPTER III

FINDINGS AND INTERPRETATIONS

In fifteen months of study, fifty D. elator were marked and

recaptured 233 times (see Table 1); 52% of them were captured four

times or more. One male was recaptured 19 times in three months.

A female was recaptured 12 times. Grid I, trapped 4418 trap-nights,

provided the most data in numbers of recaptures, trap range, and e

distances between captures of individuals.

D. elator burrows were found in small isolated areas of clay

loam soil with scattered mesquite trees. The ground was relatively

barren of grass cover; dense grass cover seemed to delimit the burrow

systems and activity of the kangaroo rats. The results of trapping

similar areas, but with rocky soil, produced only a single D. elator. ; l

No D. elator burrows could be found in the area, suggesting that 3 _ _ _ _ _ _ _ _ _ ^

this animal was not resident to this area. No burrov/s v/ere found in \ rocky substrates.

Dalquest and Collier (1964) noted the lack of D. elator in

sandy areas. Efforts to locate D. elator in the sandy bed of the Red

River in the northern part of Wichita County were unsuccessful, al-

though populations exist nearby. Near the lowa Park Lake, D. elator

was found living in sand. This area is covered by a subsoil sand

from which the topsoil v/as removed in the construction of the lake.

This, to my knowledge, is the only known instance of D. elator living

in sand.

Man-made habitats such as terraces, road grades, and dozed earth

15

16

TABLE 1

Summary of data obtained from live-trapping four areas i'i

GRID I

Total trap-nights ^

Total captures

Dipodomys elator

Total captures

Females

Males

Total individuals

Total per acre

Residents per acre

Total individuals:

Peroqnathus hispidus

Peroqnathus merriami

Siqmodon hispidus

Peromyscus spp.

Reithrodontomys sp.

Neotoma sp.

\m 501

"

107

8

n 23

8.5

5.5

22

17

13

41

10

5

GRID II

856

196

54

2

8

10

14

10

20

11

0

15

4

0

GRID III

1000

82

20

2

3

7

4.9

3.5

12

10

3

6

4

0

GRID IV 1

2046

173

52

3

7

10

7

6.3

31

14

6

9

0

1

TOTAL

8320

952

233

15

29

50

85

52

22

71

18

6

17

are seemingly preferred by D. elator. It was found present around

the edges of fields with burrows in the loosened soil and where the

construction and grading of dirt roads produced loose dirt at the

shoulders of the roads. In all instances studied, D. elator dis-

tribution was arranged in a linear pattern along a road or field edge

unless adjacent areas were essentially barren of plant cover.

Animals trapped in these areas with D. elator were: Peromyscus

spp., Reithrodontomys spp., Neotoma sp., Sigmodon hispidus,

Perognathus hispidus, and Perognathus merriami. Sigmodon hispidus x

and D. elator may encounter one another occasionally, but high , i

grass seems to serve as an effective ecological boundary betv/een i

them. My observations suggest it is rare for either to encroach l

upon the habitat of the other. D. elator never went into the grass ] 3

unless frightened or surprised, and even then the animal left the (

grass quickly for the barren area. S. hispidus showed a clear pre-

ference for dense grass.

Presence of droppings, dens, and tracks on the study areas and

sight observations revealed the presence of: coyote (Canis latrans),

striped skunk (Mephitis mephitis), cottontail rabbit (Sylviligus sp.),

rattlesnakes (Crotalus spp.), thirteen-lined ground squirrel

(Citellus tridecemlineatus), coachwhip snake (Masticophis flagellum),

racer (Coluber constrictor), ornate box turtle (Terrapene ornata),

horned lizard (Phyrnosoma cornutum), and six-lined racerunner

(Cnemidophorous sexlineatus).

D. elator lives in a clay loam soil v/ith burrows either under

'''''''

18

a mesquite tree or a mound of dirt (see Fig. 6). No burrows were

found under flat barren ground. Burrow systems in firm soil were

approximately eighteen inches deep in most cases, and were complex

with many interwoven tunnels, some of which were only one inch below

a tunnel above. Burrows in the sandy area of the lowa Park Lake were

less complex and tunnels were not as closely interwoven. In the sides

of tunnels were scattered food-storage caches filled with grass and

seeds. Caches for other Dipodomys spp. are mentioned by Culbertson

(D. nitratoides, 1946), Hawbecker (D. venustus, 1940), Reynolds ><

(D. merriami, 1958), and Tappe (D. heermanni, 1941). A nest was n H

found in each burrow close to the bottom of the complex of tunnels. 'J c

Burrows opened in several directions from each system and were two ; j

to four inches in diameter. They were usually left open although 3

plugged burrow-openings were observed (see Fig. 7). Closed tunnels t

inside burrow systems were found. One individual ran into an opening

of a burrow complex after being released, reappeared at another

opening, exited, and dug out still another opening previously filled

with loose dirt. This burrow opening v\fas plugged within seconds after entry.

Carpenter (1966) and Schmidt-Nielsen (1950) cite the burrow

as being important in reducing evaporative losses by providing a cool

atmosphere of relatively high moisture content. The highest temper-

ature recorded in a D. elator burrow was 95° F. Similar temperatures

were found in burrows of D. aqilis and D. merriami by Carpenter (1966).

Burrow temperatures were found to vary little in comparison to out-

19

1 , í 1 1 1 t

; • , j • ^

1 • ')/ í

r

FIGURE 6

Habitat of Dipodomys elator on Grid III. Burrow openings are visible under the mes-quite tree and in the mound behind the tree

21

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s ' jHnHijliÍJHnHijliÍJHnHijliÍJHnHijliÍJHni

i i i i i ••••••• i i i i i ••••••• i i i i i ••••••• i i i i i ••••••• i i i i j

i i i i i inHniiiii inHniiiii inHjjjii i i i i i 11 (' i 1 (' i '." i i i i i i '." i i i i i i "'

I . . . i i i i i i i i i ! ; ! i i ; i i i i i i ! ; ! i i ; i i i i i i ! ; ! i i ; i i i i i i ! ; ! i i ; i i i i i i i i ! ! i i i i i i i i i i i i i i i i î i i i i i i i i i i i î i i i i i i i i i i i î i i i i i i i i i i i î i i i i i i i i ii iiiiiiiiiiii!niiiiiiiii!niiiiiiiii!niiiiiiiii!niiiiiiiini

í Í imii i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

l î i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i i

2,iLa222^La222^La222^La222^La222^La222^La

FIGURE 7

Open and plugged burrow openings of Dipodomys elator.

22

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iA.Í^ ... •m^^k

' » . j ^ ) ^

^^ '^

*m

\P

*

I

23

side temperatures. The probe of a Tempscribe v/as placed approxi-

mately 24 inches inside a burrow at an estimated depth of 7 inches

below the surface of the soil May 2-8, 1967. The temperature of the

burrow varied only 5° (60-65° F.) during the week whereas the outside

temperature varied 52° (45-97° F.). Similar comparisons in which

the probe was placed approximately 18 inches inside the burrow opening

of another system yielded larger variations - as much as 25° F. during

a week. Outside temperatures near this burrow opening varied as much

as 50° F. 1 ><

My observations indicate that some individuals have a larger n

home range than v/as revealed by trap ranges. Stickel (1954), Blair :J >•

(1941), Hayne (1949, 1950), and Burt (1943) discuss the uncertainty I

concerning the determination of home range. Hayne (1950) found a J

positive relationship between apparent size of home range and the 3 V

distance used between traps with Microtus. On several occasions an

animal, when released, ran outside the trap range to a burrow opening,

passing several other burrow openings on the way. My observations

suggest that D. elator ranges throughout suitable habitat, but this

is quite restricted.

The average trap range for both sexes of D^ elator captured

four or more times was .20 acre. Males used in the determination of

the trap ranges averaged 8.1 captures each whereas females averaged

7.1 captures each.

The largest trap range for any individual was a female with

.49 acre (see Table 2). The largest trap range for a male was .45

24

TABLE 2

Trap ranges of female Dipodomys elator.

Grid

I

I

I

I

I

AVERAGE

II

II

AVERAGE

III

III

AVERAGE

IV

AVERAGE

FINAL AVERAGE

Range in acres

.11

.34

.07

.49

-43

.29

.14

.09

.12

.07

.11

.09

.11

.11

.20

Times captured

7

11

5

12

11

9.1

4

6

5

5

4

4.5

6

6

7.1

Max. distance between caotures

105

175

55

356

305

199

150

90

120

75

90

83

92.5

92.5

149

H 1

25

acre (see Table 3). Both of these individuals were captured on Grid

I where the average trap ranges were .26 acre for males and .29 acre

for females. A U trap ranges were calculated using the inclusive

boundary strip method described by Blair (1940).

Abandoned dirt roads barren of grass v/ere on three of the grids.

Trap ranges near these roads had a more linear pattern than other

trap ranges. None of the trap ranges encompassed a sizable mesquite

clump or a stand of heavy grass, and they coincided roughly v/ith

the shape of the barren areas. Trap ranges on Grid II were the small- >< • >

est (see Fig. 3). Because burrows were located in the terrace row J

in the middle of the grid, size of trap range may have been restrict- j

ed. Burrows were scattered on the other three grids. Small size " 1

of trap range on Grid III may have resulted from small samples size. J

In trapping areas, most D. elator were erratic in their pattern ^

of movement when released but did not leave the vicinity of the trap

range. The maximum distance traveled between traps by a male was

285 feet (see Table 3), whereas two females moved 305 and 356 feet

(see Table 2). Kangaroo rats traveled over 1000 feet in some cases

on roads. Roads and terraces seemingly facilitate the route of

movement selected by D. elator.

Populations of D. elator were seemingly highar in mid-winter

and late spring (see Tables 4-7). A decline in density in July was

indicated by trapping records. This decline could have resulted from

seasonal bait acceptance (see Fitch, 1958;. This is further supported

26

TABLE 3

Trap ranges of male Dipodomys elator.

Grid Range in acres

Times captured

Max. distance between captures

I

I

I

I

I

AVERA6E

II

II

II

II

II

AVERA6E

III

AVERA6E

IV

IV

IV

IV

AVERA6E

FINAL AVERA6E

.16

.14

.45

.43

.11

.26

.04

.13

.24

.10

.12

.13

.10

.10

.35

.29

.12

.33

.27

.20

6

5

19

8

5

8.6

4

7

16

4

7

7.6

4

4

14

6

11

6

9.3

8.1

135

135

285

275

95

185

55

112

127

70

75

88

102

102

200

231

94

178

176

145

•4

n

I j

w

l l l

27

TABLE 4

Percentage of Dipodomys elator captured

Month

Dec. '65

Jan. '66

Feb. '66

March '66

April '66

May '66

June '66

July '66

August '66

per trapping effort

Total D. elator

6

6

5

8

6

2

9

5

1

Trap-nights

168

288

384

813

525

210

1230

700

100

on Grid I

% per trap-night per month

3.57

2.08

1.30

.985

1.14

.954

.733

.715

1.00

% per total trapping effort

.136

.136

.113

.181

.136

.0453

.204

.113

.0226

•H 1

•<

» )

A 1 i

TABLE 5

Percentage of Dipodomys elator captured per trapping effort on Grid II

Month

March '66

April '66

May '66

June '66

Total D. elator

7

18

5

Trap-nights

216

240

160

240

% per trap-niqhl per month

4.17

2.92

11.3

2.80

j per total trapping • effort

1.05

.818

2.15

.584

28

TABLE 6

Percentage of Dipodomys elator captured per trapping effort on Grid III

Month

Aug. '66

Dec. '66

Jan. '67

Total D. elator

2

4

4

Trap-nights

500

300

200


0.40

L33

2.00


.20

.40

.40

H

•<

»

1 i

TABLE 7

Percentage of Dipodomys elator captured per trappmg effort on Grid IV

Month

May '67

June '67

July '67

Total D. elator

6

9

Trap-nights

1030

1016

360

% per % per total trap-night trapping per month effort

.582

.886

.293

.440

29

by observations of activity made by nighttime driving. There was

continued use of burrows, run-ways, and scratching sites on the grids

in the summer. Captures of other rodents also decreased as avail-

ability of new vegetation increased.

High mortality of D. elator in traps may have influenced the

population data obtained in the winter and early spring. Although

nesting material of cotton and grass was provided in the traps, it

proved inadequate in subfreezing temperatures. In cold v/eather, it

was necessary to check traps twice a niqht to prevent casualties. T

<

Temperatures of 40-70° F. with moist conditions proved fatal to the i . . . i

rats if they were caught early in the night. ' m

D. elator entered both closed and open unbaited traps. This I

occasionally resulted in the death of animals, particularly between [

trapping periods. i

It seems unlikely the total population of rats on the areas of

study are represented in the trapping results. Dice (1931) and

Murray (1957) discuss the bias introduced by trapping grids and

encourage the use of combinations of population sampling techniques.

On each grid, active burrows were observed that released rats never

entered. The total population, therefore, was estimated to be slight-

ly greater than the total number of residents captured on a given

area (see Table 1). Use of the Lincoln Index provided an estimate of

the numbers of D. elator on the four grids (see Table 8). This number

proved slightly less than the calculated number of residents.

Perognathus hispidus and P_̂ merriami were caught on the same

30

TABLE 8

Population of Dipodomys elator as estimated by Lincoln Index

Month Grid I Grid II Grid III Grid IV

December, 1965

January, 1966

February, 1966

March, 1966

April, 1966

May, 1966

June, 1966

July, 1966

August, 1966

December, 1966

January, 1967

May, 1967

June, 1967

4.0

2.7

3.5

6.2

6.0

6.0

6.5

9.6

8.0

7.8

6.8

7.0

7.0

2.0

2.5

3.0

5.1

7.3

1 <

1

Average 5.8 7.2 2.5 6.2

11111III

H

31

areas and seemed to be limited to a similar habitat as D. elator.

Relatively large numbers of Peromyscus spp. were caught, but they did

not appear to be identified as closely with the habitat of D. elator

as P. hispidus and P. merriami. Trap ranges of these four species

overlapped considerably. The relative abundance of the four species

and their relative activity as expressed by captures is represented

in Figures 8-11.

P. merriami may have been hibernating during the colder months

(see Tables 9-12). It did not appear on Grid I until the temperature <

low reached 58° F. in March. The only time this species was captured J

in winter months was on a relatively v/arm night (low of 45° F.) on

Grid III. As it became warmer, the number of P. merriami trapped in- '

creased markedly until a population peak was reached in August. '

P. hispidus was also more abundant in the warmer months and ;

remained sporadically active in colder months (see Tables 13-16).

This species was trapped each month on all four grids. The population

reached a peak in the summer.

The data suggest no well defined breeding periods for D. elator.

More females were found in breeding condition in March than any other

month, although some were lactating in each month trapped from late

December to May. Some males, judging from extended scrotal sacs,

were reproductively active throughout the study. Scrotal sacs were

subject to extension and retraction within a 24 hour cycle. In some

cases, only one testis would be distended.

A nest containing four young D. elator v/as discovered in digging

32

í V

-^MHMMMbH

u

FI6URE 8

6RID I

Relative abundance of species expressed as a percent of total individuals captured each month.

f r.

CJ: X > z <

Dipodomys elator ~ Peirognath'us hispidus -

Peroqnathus merriami Peromyscus spp.

3

Relative activity of species expressed as a percent of total captures.

í«r

33

Dec. Jan. Feb. March '65 '66 '66 '66

April May June •66 '66 '66

J u 1 y A u g . '66 '66

-t 1 <

1

Dec. Jan. Feb. March April May June July Aug. '65 '66 '66 '66 '66 '66 '66 '66 '66

n t I

f r

FI6URE 9

6RID II

!! I ! i tt I I I !! I ! !

1 1 1 ! M I ! i ! ; t

• í.

Relative abundance of species expressed as a percent of total individuals captured each month.

h

' 'f %

r.

c

'.'• Rí

1 1 V , ! •! •! í

i 1 1 1 ..'-•í'. .'-•í'. .'y. .'y.

'Í^ *̂ *̂ ̂*

t i i i k t t t

Dipodomys elator Peroqnathus merriami Perognath'us hispidus Peromyscus spp.


a » » »

f '^ '^ '^

t t; t; t; \ \ \ \ u t t t

35

60 1

March April May June '66 '66 '66 '66

60 "

50 -

40 -

30 "

20 -

10 •

\

\

\ \-, • >

y/ V

March •66

\ *

\

\

April •66

• •

/

May •66

/

/

June •66

% •

\ f •

I

i * k í

r i \

!ll! * • * . ' -

î \ \'

• > • • >

•» f • •

ÍM

FIGURE 10

GRID III

Relative abundance of species expressed as a percent of total individuals captured each month

Dipodomys elator Perognathus merriami Perognathus hispidus Peromyscus spp.


37

50

40

30

20

10

\

• \

\

/ /

/ ^ \ « ' '. . • •

• ••

\

>

Aug. Dec. Jan •66 '66 '67

Aug. Dec. Jan, •66 '66 '67

>«'

FIGURE 11

GRID IV

Relative abundance of species expressed as a percent of total indiYiduals captured each month.

m

l a î r*

Dipodomys elator Perognathus hispidus

Perognathus merriami Peromyscus spp.


39

60-

50-

40"

30-

20-

10"

•

•

1

•

•

* *

• •

\ •

May June July •67 '67 «67

• 1

I 1 * í í

1 i ( j i

6 0 -

5 0 -

4 0 -

3 0 -

2 0 -

10 •

\

X

-s

May •67

• •

\ .

- i <

C\ June

•67

• • • •

p

\

July •67

40

TABLE 9

Percentage of Perognathus merriami captured per trapping effort on Grid I

Month Total P. merriami

Trap-nights



Dec. '65

Jan. '66

Feb. '66

March '66

April '66

May '66

June '66

July •̂ ^

August '66

0

0

0

4

5

4

10

12

5

Percentage

168

288

384

813

525

210

1230

700

100

TABLE 10

.492

.952

1.90

.813

1.72

5.00

of Perognathus merriami ca ptured

.0905

.113

.0905

.227

.273

.113

per trapping effort on Grid II

Month Total P. merriami

Trap-nights

March '66

April •̂ ^

May '66

June '66

3

7

4

10

216

240

260

240


% per total trapping pffnrt.

1.39

2.91

2.50

416

.350

.819

-467

1.17

41

TABLE 11

Percentage of Perognathus merriami captured per trapping effort on Grid III

Month

Aug. '66

Dec. '66

Jan. '67

Total D. elator

12

0

1

Trap-nights

500

300

200


%per total trapping effort

2.40

.50

1.20

.10

TABLE 12

Percentage of Perognathus merriami captured per trapping effort on Grid IV

Month

May '67

June '67

July '67

Total D. elator

8

7

10

Trap-nights

1030

1016

360

% per

.776

.688

2i78

% per total trap-night trapping per month effort

.391

.342

.489

42

TABLE 13

Percentage of Perognathus hispidus captured

Month

Dec. '65

Jan. '66

Feb. '66

March '66

April '66

May '66

Jine '66

July '66

August '66

Month

March '66

April '66

May '66

June '66

per trapping effort

Total P. hispidus

9

12

2

Trap-nights

168

288

384

813

525

210

1230

700

100

TABLE 14

Percentage of Perognathus h per trapping effort

Total P. hispidus

5

9

7

7

Trap-nights

216

240

160

240

on Grid I


.596

.347

.261

.123

.763

.476

.732

1.72

2.00


.0227

.0227

.0227

.0227

.0906

.0227

.204

.273

.0454

ispidus captured on Grid II


2.31

3.75

4.37

2.92


.584

1.05

.816

.816

43

TABLE 15

Percentage of Perognathus hispidus captured per trapping effort on Grid III

Month

Aug. '66

Dec. '66

Jan. '67

Total Trap-P. hispidus nights

10

2

2

500

300

200


2.00

.667

1.00


1.0

.2

.2

TABLE 16

Percentage of Perognathus hispidus captured per trapping effort on Grid IV

Month Total P. hispidus

Trap-nights



May '67

June '67

July '67

8

16

18

1030

1016

360

.776

1.57

5.00

.391

.782

.880

44

up a burrov/ system in late January, 1966. These nestlings were naked

and blind. The assumed mother v/as live-trapped, and nesting material

v/as later provided in a cage in the laboratory. Efforts v/ere made

not to disturb the female and her young. She appeared to make some

attempts to care for the young, but they died within tv/o days. The

female ate one nestling.

A male and a female D. elator, each v/eighing 19 grams, were

captured in June, 1967. These v/ere the youngest individuals caught

in traps. The male was unstable in his movement after being released.

The female, estimated to be of the same litter, was more adept at

running. If the development of D. elator is similar to that of

D. merriami and D. nitratoides (Eisenberg and Isaac, 1963), these

individuals were weaned near the time of capture and were 18-20

days old. This assumption is supported by their weight, physical

appearance, and level of coordination in movement.

A young male on Grid II underwent the greatest weight-gain

during the study. He v/as captured 16 times betv/een March 14, 1966,

and June 11, 1966, and his weight increased from 30 to 64 grams.

Another male on Grid IV gained 33 grams over a period of 36 days,

whereas a male on Grid I was observed to gain only 23 grams over a

period of four months.

D. elator burrow systems seemed less dispersed than those of

D. ordii and D. mcrriami in other areas. The close proximity of

the burrow systems seems to be necessitated by the small areas suit-

able for habitat rather than any possible social affinities.

45

D. elator. when released, seemed to recognize certain burrov/s and

enter only its suspected home burrow. This behavior was modified,

however, v/hen the animals were pursued by the investigator. In cer-

tain cases released animals would enter a burrow only briefly, then

move to the assumed home burrow. Two adults were rarely observed to

enter the same burrow, although in tv/o instances young D. elator may

have occupied the sama burrow system.

Distances between burrow systems were inconsistant. Separate

burrow systems belonging to D. elator were found as close as fifteen

feet apart on Grid I. On Grid II, the burrow systems were close

together on the terrace row and individual systems could not be dis-

tinguished without digging them.

Tv/o or more D. elator were never observed together and no mul-

tiple captures were recorded. On two occasions, D. elator v/as found

in a trap with a Peromyscus sp. Attempts to keep D. elator together

in cages proved unsuccessful. On tv/o occasions when pairs were

placed in the same cage, the male died within a week. The female

was observed to harass the male by nipping him about the body. Of

approximately 90 individuals handled, only one D. elator (a juvenile)

ever attempted to bite me.

Scratching and dusting places were numerous on the trapping

areas. They were found in barren areas and seemed to be used con-

sistently judging from the prevelance of loose, powdery dust (see

Fig. 12). Footprints, tail-drag marks, and scratched imprints of

toenails could be distinguished. Trails and runways v;ere not

46

:l

^^^^i^jujttímasåai

a i

i

FIGURE 12

Dipodomys elator dusting and scratching area.

48

conspicuous because of the barren type of habitat. In more abundant

vegetation, however, definite runways could be distinguished. These

did not have the tunnel-appearance of those of Sigmodon hispidus.

D^elator v/as observed active in weather ranging from hot to

cold, windy to calm, and wet to dry; they were also observed in moon-

light and darkness. They were most active two to three hours after

darkness (see Table 17). Although it is generally unusual to find

kangaroo rats foraging in the moonlight, six individuals were observed

on or near a road v/ithin a distance of 1.5 miles in bright moonlight

on December 29, 1965. Chew and Butterworth (1964) noted that a full

moon did not seem to deter captures of D. merriami. Captures of

D. elator were made during the coldest times of the year (see Tables

4-7), and tracks and open burrows v/ere observed with four inches of

snow on the ground in 1966 (see Fig. 13).

D. elator is capable of producing a thumping noise similar to

that described by Eisenberg (1963) for four species of Dipodomys.

A few rapid thumps were heard within seconds after the entry of a

single D. elator into a burrow. This thumping was repeated after

a short time, and then scratching sounds could be heard from within

the system. Other than thumping, the only noise produced by kangaroo

rats in this study was the constant squealing of one young (24 gram)

male v/hen I markcd him. No explanation could be given for this

squealing behavior other than possible fright. He continued squealing

after being released.

According to Bailey (1905), Professor D. E. Lantz noted a

49

TABLE 17

Record of nighttime observations of D. elator

Time

Sundown

Sundown - 10 pm

10 pm - midnight

Midnight - 2 am

Hours driven

20

10

12

6

D. elator ôFserved

2

7

42

14

D. elator per hour

.10

J

3.5

2.34

IM'BS

FI6URE 13

Tracks and open burrow of Dipodomys elator in snow.

4. .i,.

52

preference of D. elator for the vicinity of "houses, outbuildings,

and caves made for storing vegetables." The closest to human dwellings

recorded for D. elator was 200 yards. Residents of this dwelling said

that a number of years ago some kangaroo rats had taken up residence

under a cattle loading ramp adjacent to a barn, and approximately

50 yards from the house. No long-time resident could remember the

rats being closer to a dwelling.

CHAPTER IV

SUW1ARY AND CONCLUSIONS

An ecological study of Dipodomys elator was conducted from

September, 1965, to July, 1967, in Wilbarger and Wichita counties,

Texas. Principal study areas v/ere 5 to 10 miles northwest of lowa

Park, Texas. A total of 9,796 trap-nights revealed: (1) habitat of

D. elator consists of a clay loam soil in areas sparsely covered with

grass; (2) distribution and migration of D. elator has been facil-

itated by the building of roads and terrace rows by humans; (3) bur-

row systems were complex with a number of plugged and open entrahces;

(4) trap ranges for 15 males and 9 females averaged .20 acre for each

sex although observations made v/hile driving and trailing suggest

a larger home range; (5) populations of D. elator were estimated to

be from 4 to 11 per acre on the four areas of study; (6) D. elator

had higher trap-mortality due to adverse v/eather conditions than

other rodents captured on the same areas; (7) observations indicate

females may breed as early as December and as late as April, and some

males were in breeding condition each month of the study; (8) al-

though burrow systems v/ere found close together, D. elator appears

to be a solitary animal except at times of breeding.

53

LITERATURE CITED

Bailey, Vernon. 1905. Biological survey of Texas. N. Amer. Fauna, 25:1-222.

Blair, W. F. 1940. Home ranges and populations of the meadow vole in southern Michigan. J. Wildl. Manage., 4:149-161.

Blair, W. F. 1941. Techniques for the study of mammal populations. J. Mammal., 22:148-157.

Blair, W. F. 1949. Extensions of the known ranges of three species of Texas mammals. J. Mammal., 30:201-202.

Blair, W. F. 1954. Mammals of the mesquite plains biotic district in Texas and Oklahoma and speciation in the central grasslands. Texas J. Sci., 3:248.

Burt, W. H. 1943. Territoriality and home range concepts as applied to mammals. J. Mammal., 24:346-352.

Carpenter, R. E. 1966. A comparison of thermoregulation and v/ater metabolism in the kangaroo rats D. agilis and D. merriami. Univ. California Press, Berkeley, 36 pages.

Chew, R. M. and B. B. Butterworth. 1964. Ecology of rodents. J. Mammal., 45:203.

Culbertson, A. E. 1946. Observations on the natural history of the Fresno kangaroo rat. J..Mammal., 27:189-203.

Dalquest, W. W. and Glen Collier. 1964. Notes on Dipodomys elator, a rare kangaroo rat. The Southwest. Nat., 9:146-150.

Dalquest, W. W. 1968. Mammals of North-Central Texas. The South-west Nat., 13:13-22.

Davis, W. B. 1942. The systematic status of four kangaroo rats. J. Mammal., 23:328.

Dice, L. R. 1931. Methods of indicating the abundance of mammals. J. Mammal., 12:376-381.

Eisenberg, J. F. and D. E. Isaac. 1963. Reproduction of heteromyid rodents in captivity. J. Mammal., 44:61-67.

Eisenberg, J. F. 1963. The behavior of heteromyid rodents. Univ. California Press, Berkeley, 100 pages.

54

55 Fitch, H. S. 1950. A new style live-trap for small mammals. J.

Mammal., 31:364-365.

Fitch, H. S. 1958. Seasonal acceptance of bait by small mammals. J. Mammal., 1:39-47.

Grinnel, Joseph. 1921. Revised list of the species in the genus Dipodomys. J. Mammal., 2:94.

Hawbecker, A. C. 1940. The burrov7ing and feeding habits of Dipodomys venustus. J. Mammal., 21:388-396.

Hayne, D. W. 1949. Calculation of size of home range. J. Mammal., 30:1-18.

Hayne, D. W. 1950. Apparent home range of Microtus in relation to distance between traps. J. Mammal., 31:26-39.

Hedeen, R. A. 1953. Ectoparasites occuring on mammals in the vicinity of Fort Hood, Texas. Texas J. Sci., 5:125-129.

Lidicker, W. Z. 1960. The baculum of Dipodomys ornatus and its implication for superspecific groupings of kangaroo rats. J. Mammal., 41:498.

Lidicker, W. Z. 1960. An analysis of interspecific variation in the kangaroo rat Dipodomys merriami. Univ. California Press, Berkeley, 212 pages.

McCarley, W. H. 1954. Fluctuations and structure of Peromyscus gossypinus populations in eastern Texas. J. Mammal., 35:526.

Merriam, C. H. 1894. Preliminary descriptions of eleven new kangaroo rats of the genera Dipodomys and Perodipus. Proceedings Biol. Soc. Washington, 9:109-116.

Murray, K. F. 1957. Some problems of applied small mammal samp-lings in western North America. J. Mammal., 38:441-451.

Packard, R. L. and F. W. Judd. 1968. Comments on some mammals from v/estern Texas. J. Mammal., 49:535-538.

Reynolds, H. 6. 1958. The ecology of the Merriam kangaroo rat on the grading lands of southern Arizona. Ecol. Monogr., 28:111-127.

Schmidt-Nielsen, B. and K. Schmidt-Nielsen. 1950. Evaporative water loss in desert rodents in their natural habitat. Ecology 31:75-85.

1

56 Setzer, H. W. 1949, Subspeciation in the kangaroo rat, Dlpodbmys

ordll. Univ. Kans. Publ. Mus. Nat. Hist., 1:473-573.

Stlckel, L. F. 1954. A comparison of certain methods of measurîng ranges of small mammals. J. Mammal., 35:1-15.

Tappe, D. T. 1941. Natural history of the Tulare kangaroo rat. J. Mammal., 22:117-148.

ecological study of the texas kangaroo rat

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