HARVARD UNIVERSITY

Library of the

Museum of

Comparative Zoology

MCZ
LIBRARY
OCCASIONAL PAPERS

of the OCT 0 9 1990

MUSEUM OF NATURAL HISTORY
The University of Kansaj^^^^^^^^f^^^
Lawrence, Kansas

NUMBER 139, PAGES 1-27 11 OCTOBER 1990

THE ANNUAL CYCLE OF THE MEXICAN
PRAIRIE DOG {CYNOMYS MEXICANUS)

Julian Trevino-Villarreal"

Mexican prairie dogs {Cynomys mexicauus Memam. 1892) (Fig. 1), or
"perritos llaneros," are endemic to northeastern Mexico (Ceballos-G. and
Wilson. 1985) with a restricted, relictual distribution ot less than 800 square
kilometers in the Mexican states ot Coahuila. Nuevo Leon. San Luis Potosi,
and Zacatecas (Fig. 2). The species is confined to valleys, prairies, and
intermontane basins at elevations between 1600 and 2000 m.

Where it occurs, Cynomys mexicauus plays an important ecological and
economic role, both as a link in the food chain and as a modifier of soil
structure through fossorial activity. Prairie dogs are considered to be pests by
many cattle raisers and agriculturists. Jimenez-Guzman (1976) reported that
farmers and ranchers from Tokio, Galeana, Nuevo Leon, frequently shot and
poisoned prairie dogs. Also, placing obstacles such as tree branches in buiTow
openings is often an effective and inexpensive control method.

Little biological information is available on C. mexicanus. except for a
single laboratory study of growth (Pizzimenti and McClenaghan, 1974).
Mexican prairie dogs are listed as vulnerable by the lUCN and as endangered
by the USDI, and the species is on Appendix I of CITES (Nowak and Paradiso,

'Division of Mammals. Museum of Natural History, Dyche Hall, and Department
of Systematics and Ecology, Haworth Hall, The University of Kansas, Lawrence,
Kansas 66045-2454, USA. Present address: Division de Recursos Naturales, Instituto
de Ecologia y Alimentos, Universidad Autonoma de Tamaulipas, 13 Boulevard
Adolfo Lopez Mateos 928, Ciudad Victoria, Tamaulipas, Mexico.

OCCASIONAL PAPERS

^

-"**». .4^

h^ '^

#

Fig. 1. A Mexican prairie dog {Cynomys mexicanus) in summer pelage.

1

1983). The purpose of this study was to gather baseline information on the
reproduction, growth, development, molt patterns, and colony organization
of Cynomys mexicanus.

METHODS AND MATERIALS

A colony of Mexican prairie dogs occupying a 9.55 ha area was chosen for
study. Sixty-four animals ( 1 8 adults or adult-size yearlings. 25 young born in
late May 1985 that became yearhngs in mid-May 1986, and 21 young bom
in early March 1986) were trapped over 24 sampling periods (Table 1),
marked, and released from early October 1 985 to late September 1 986. In the
analyses reported below, the 18 adult-size animals captured from October
1985 to April 1986 were assumed to represent adults, although some may
have been yearlings that had already achieved adult size. Thirty-six additional
animals (5 adults or adult-size yearlings and 35 young born in late January
1987 ) were also marked and released from early October 1 986 to late January
1 988. Colony residents were captured in National live traps baited with whole
oats and alfalfa. Prairie dogs residing outside the study colony were captured
by flooding their burrows and capturing them as they emerged. Every trapped
individual was marked with Nyanzol-A fur dye (Fitzwater, 1943) for field
identification and with a numbered tag in each ear. Any lost ear tags were

MEXICAN PRAIRIE DOG ANNUAL CYCLE

27

24-

Coahuila

27

24°

Fig. 2. The distribution of the Mexican prairie dog {Cynomys mexicauus). The
star (*) indicates the location of the study site at El Tokio. Nuevo Leon, Mexico.

replaced upon next capture. Before release, each animal was examined to
determine its sex, reproductive status, weight, tail length, and details of pelage
condition. All active burrows in the study colony were mapped to facilitate
recording of movement. Weather data (precipitation, temperature, days of
frost) were recorded at the study site. Long-term weather trends were obtained
from three nearby weather stations. Weather data from 1985 to September
1986 were obtained froin the El Potosi weather station. Weather data from
October 1986 to January 1988 were obtained from the Rancho San Roberto
weather station, which has a similar climatic pattern to the closer El Potosi
weather station; the El Potosi weather station has not issued a weather report
since October 1985.

Vegetation was sampled on randomly distributed 1 m- exclosures. Vegetation
samples, cut to 3 cm above the soil surface, and notes on vegetative growth
were made every month from November 1985 to October 1986. Dry weight

4 OCCASIONAL PAPERS

Table 1 . Dates of sampling of a colony of Mexican prairie dogs from El Tokio,
Galeana, Nuevo Leon, Mexico.

Sampling

Sampling

period

Date

period

Date

1

16-19 October

1985

13

18-23 July 1986

2

4-8 November 1985

14

8-13 August 1986

3

25-29 November 1985

15

6-10 September 1986

4

16-21 December 1985

16

25-29 September 1986

5

20-25 January

1986

17

20 December 1986

6

12-17 February

1986

18

27-28 January 1987

7

4-10 March

1986

19

21 February 1987

8

24-29 March

1986

20

11-13 April 1987

9

14-18 April

1986

21

1^ June 1987

10

5-7 May

1986

22

23-25 August 1987

11

25-29 May

1986

23

11-15 October 1987

12

13-16 June

1986

24

20-22 January 1988

of vegetation was obtained by oven-drying samples at 60°C for 48 hours.
Percent ground cover was estimated by using a Modified Step Transect
Method called "100 in 500" (Avalos-Marin, in prep.). Transects of 500 steps
were traversed, and notes on vegetation were taken at contact points every 5

steps.

Percentage vegetative cover was obtained by the formula:

% Cover =

Total number of plant contacts x 100
Total number of points

Prairie dogs were placed in three age classes (Rayor, 1985): ( 1 ) young,
during the first summer of life; (2) yearlings, during the second summer of
life; and (3) adults, two years of age or older.

For emergent young, means of measurements for the total litter and for
each sex were plotted against estimated age in days (using the technique of
Pizzimenti and McClenaghan, 1 974 ). Student's /-tests were used to test sexual
dimorphism. The instantaneous growth rate (IGR) was calculated for each
phase of constant growth (Brody, 1945).

DESCRIPTION OF THE STUDY SITE

Ejido El Tokio ("Ejido" is an agricultural unit, established by Mexican law,
which cannot exceed 10,000 ha) is located in Galeana County, Nuevo Leon,

MEXICAN PRAIRIE DOG ANNUAL CYCLE 5

Mexico, at 24°38' to 24°44' N and 100° 11' to 100° 17' W. Mean elevation is
1 865 m. Ejido EI Tokio is in the Sierra Madre Oriental geomorphic zone, and
sediments from the Upper Jurassic, Lower Cretaceous, and Middle Cretaceous
occur there (Mulleried, 1944). The soil of the study area is a xerosol
(DETENAL, 1975). characterized by a soft, saline surface horizon.

Grasslands at Ejido El Tokio can be classified into three zones ( DETENAL,
1975). Zone I was relatively undisturbed, and Mexican prairie dogs were
abundant. The 9.55 ha study site, located in this zone, was a halophyte
grassland (DETENAL, 1 975 ) dominated by Muhlenheri^ia villiflora and Frank-
eiila i>ypsopluki. Annuals began appearing by April in 1986 (Avalos-Marin,
in prep.). Small patches of shrubs such as Koeberlinia spinosa, Opuntia
imhricata, Larrea thdentata, and Condalia ericoides also occurred in this
zone (Trevino-Villarreal. 1981). Zone II also was a halophyte grassland
(DETENAL, 1975) dominated by Muhlenhergia villiflora, Arisfida barbata,
Frankenia gypsophila. andBouteloua chasei (Fig. 3). Annuals began appearing
by May in 1986 (Avalos-Marin, in prep.). All of the species of shrubs found
in Zone I also occuiTcd in Zone II (Treviiio-Villaneal, 1981). In late January
1988, the study site and most of Zone I were plowed, and the entire colony of
Mexican prairie dogs disappeared. In Zone II agriculture has spread rapidly
in recent years, and populations of Mexican prairie dogs are being limited by
human control. Zone III contains most of the human population of the Ejido,
and the area is devoted solely to agriculture. Mexican prairie dogs no longer
live in Zone III. Old residents of El Tokio say that Mexican prairie dogs were

Fi2. 3. Grassland Zone II. Cerro San Juan is on the left.

6 OCCASIONAL PAPERS

numerous in this region before extensive agriculture was established. Zone III
was so altered by agriculture that native vegetation no longer occurred there
(DETENAL, 1975).

Climate

Two subtypes of climate occur on the grasslands of El Tokio, according to
the Secretaria de Programacion y Presupuesto climate map (SPP, 1981),
which is based on a Koppen climate classification as modified by Garcia
(1973). Zones I and III have a climate classified as BS, kx' and belong to the
temperate semi-dry climate subtype. Zone II has a climate classified as
BS„ kx' and belongs to the temperate dry climate subtype. A second type, Cx'
(cold dry climate), occurs in the area occupied by desert thicket and montane
vegetation of the Ejido.

General weather trends were obtained from the weather stations nearest
each zone — El Potosi and Rancho San Roberto (temperate semi-dry), and
Raices (temperate dry). Two short periods of rainfall, one in August and the
other from October to January, occur in Zones I and III. Precipitation occurs
in an irregular manner and is often ton-ential. December is the wettest month
of the year with 45.9 mm of precipitation, while March is the driest with 6.8
mm. The annual mean temperature is 16.2°C. In Zone II a pronounced dry
season occurs from October to April. Precipitation in this zone is also irregular
and often tonential. August is the wettest month with 44.0 mm of precipitation
and March is the driest with 1 1 .6 mm. The annual mean temperature is 1 6.7°C.
Frost occurred on the study site between 5 November 1985 and 27 March
1986(Trevifio-Villarreal, 1988).

RESULTS

Reproduction

By the third week of December 1985 all three adult male prairie dogs
captured on the study site had begun to exhibit scrotal testes. All five captured
in the last week of January 1986 had fully scrotal testes. Testes of adult males
remained enlarged until mid-July 1 986. Likewise, all six young male Mexican
prairie dogs born in late May 1985 had enlarged testes by the end of March
1986, and they remained enlarged until mid-July. In contrast, young male
prairie dogs born in early March 1986 did not exhibit enlarged testes during
the reproductive season of 1986.

Adult female prairie dogs had well-developed nipples and swollen vulvae
from mid-February to mid-June 1986, when nipples regressed to a barely
visible state and vulvae exhibited almost no swelling. Yearling and young
female prairie dogs never displayed nipple or vulvar development during the
reproductive season of 1986.

MEXICAN PRAIRIE DOG ANNUAL CYCLE 7

Seven of eight marked adult females had litters of young in 1986, with a
total of 28 young emerging above ground (Table 2). The number of emergent
young per litter averaged 4.0 for 1986. Emergence of young began in mid-
April 1986. The mean age for the young at first capture was estimated to be
45 days (range, 43^7), suggesting that they were born by early March 1986.
A young male prairie dog, not caught at the study site but in the same zone,
was the same age as the young on the study site.

In contrast, a young male captured in Zone 11 on 1 July 1 986 was estimated
to be 31 days old, suggesting birth in late May 1986. A male and a female
young, captured in Zone II on 19 July 1 986, were estimated to be 49 days old,
suggesting birth at the end of May. These age data suggest that prairie dogs
in Zone II bred about 2'/: to 3 months later than those in Zone I in 1986. Two
adult and seven yearling Mexican prairie dogs captured on the study site by
the second week of April 1 987 exhibited fully scrotal testes. In contrast, young
male prairie dogs that were bom in late January 1987 did not develop scrotal
testes in their first year of life. Adult and yearling female prairie dogs had
well-developed nipples and swollen vulvae from mid-April to early June
1987.

All 6 adult and 14 yearling females marked in 1987 had litters of young.

Table 2. Numbers of lactating females, litters, and sexes of captured young, by
groups, in 1986 and 1987. See text for further discussion of groups.

Group

Lactating
Adults Yearlings

Litters

Young

Mean
young/

no.

no.

Cf

9

Unmarked

Total

litter

1986

I

4

4

6

7

3

16

4.0

II

1

1

1

2

1

4

4.0

III

0

0

0

0

0

0

0

IV

1

1

2

2

0

4

4.0

V

1

1

0

1

3

4

4.0

VI

0

0

0

0

0

0

0

Total

7

7

9
1987

12

7

28

4.0

I

3

5

8

9

5

23

37

4.6

II

0

2

2

I

0

7

8

4.0

III

0

2

2

1

2

7

10

5.0

IV

1

3

4

4

3

12

19

4.8

V

1

1

2

I

0

7

8

4.0

VI

1

1

2

6

3

0

9

4.5

Total

6

14

20

22

13

56

91

4.5

8 OCCASIONAL PAPERS

with a mean litter size of 4.5 (Table 2). The mean age of young at first capture
at the study site was estimated to be 74 days (range, 69-79), implying birth
by late January 1987. The mean age of seven male and five female young in
Zone I first captured on 3 and 1 6 October 1 985 was estimated from weight and
tail length data (Table 3) to be 1 30 days, corresponding to a birth date of late
May 1985. While this estimate is subject to more variation than estimates of
age of younger Cynomys, it suggests that mean date of breeding in Zone I
varied by several months from year to year.

Size and Growth

Young

Body weight and tail length were recorded from 1 04 Mexican prairie dogs
at the study site, and 10 additional animals from four other localities. Young
males born in late May 1985 were always heavier than females (Table 4). The
mean weight of young males and young females did not differ significantly
from mid-October 1985 to early March 1986, except for 191 days of age (mid-
December 1985; / = 3.1, /* < 0.02). The difference became statistically
significant at 288 days of age (late March 1986; t = 2.2. P < 0.05). Sexual
dimoiphism of tail length of these young Mexican prairie dogs was statistically
significant at 269 days of age with male tails being 5.6% longer than those of
females (early March 1986; t = 2.3, P < 0.05).

The mean weight of young males born in early March 1986 (// = 9) always
exceeded that of females (/; = 1 2 ). The difference became statistically significant
at day 140 (mid-July 1986; t = 2.3, P < 0.05). when males averaged 69.4 g

Table 3. Mean weights and tail lengths of young male and female Mexican prairie
dogs (cohort bom early March 1986) from mid-April 1986 to late September 1986. See
Table 1 for dates of sampling periods. (Sample size given in parentheses.)

Sampling Mean weight (g)^

Mean tail h
Young Cfd"

jngth (mm)

period

Young Cfd"

Young 99

Young 99

9

159.6 ±25.2(5)

141.4±12.4 (5)

56.2±2.8(5)

54.0±6.7 (5)

10

244.2+27.8(9)

235.7±2 1.2(10)

69.8±4.9(9)

68.3±3.0(10)

11

404.1 + 31.2(8)

396.0±22.7 (7)

83.0±5.1(8)

81.7±3.9 (7)

12

524.5 ±37.6(6)

479.6±32.4 (9)

92.8±4.()(6)

88.1 ±3.7 (t))

13

713.8±48.3(8)

644.4±34.2 (9)

105. 8 ±3. 5(8)

97.1±2.7 (9)

14

8 12.9± 66.5(8)

686.1 ±46.4 (7)

106.3±3.4(8)

98.0±3.8 (7)

15

957.2± 67.0(6)

819.7±43.1 (6)

1()8.0± 3.7(6)

100.2±2.0 (6)

16

987.3±65.4(7)

863.0±37.5 (7)

108.0±2.9(7)

101.4±1.8 (7)

" ± 95% confidence limits

MEXICAN PRAIRIE DOG ANNUAL CYCLE 9

Table 4. Mean weights and tail lengths of young male and female Mexican prairie
dogs (cohort bom late May 1985) from mid-October 1985 to late May 1986. See Table
I for dates of sampling periods. (Sample size given in parentheses.)

Sampling

I Mean we

ight (g)^

Mean tail length (mm)

period

Young cTcr

Young 99

Young cTcf

Young 99

1

635.9+45.0(7)

608.0±84.3(5)

83.4±12.1(7)

83.4±3.8(5)

1

661.8±47.9(8)

625.1 ±54.2(7)

88.9± 4.9(8)

81.9 + 6.1(7)

3

683.6±48.1(8)

630.4±41.4(8)

94.3± 3.5(8)

87.8±3.9(8)

4

699.3±73.1(4)

593.0±28.3(6)

94.8±13.4(4)

87.8±3.7(6)

5

672.4±49.7(8)

643.0±35.9(8)

96. 1± 5.9(8)

90.0±3.3(8)

6

693.0141.4(7)

674.3±45.1(7)

99.6± 7.3(7)

94.3 + 2.4(7)

7

764.4±32.8(7)

730.5±27.6(6)

102.3± 2.4(7)

95.0+2.5(6)

8

797.2±61.2(6)

718.0±38.6(7)

104.2± 1.2(6)

98.7 + 3.8(7)

9

851.6±69.5(7)

733.7±45.7(7)

103. 7± 2.2(7)

99.0±3.8(7)

10

865.8±61.4(7)

733.0±70.9(6)

103.7± 2.2(7)

100.7±4.0(6)

11

885.9±56.3(7)

755.5±56.2(6)

104.1± 2.1(7)

102.0±2.5(6)

^ + 95% confidence limits

heavier than females. Sexual dimorphism of tail length also was significant
at day 140 (/ = 3.8, F < 0.01 ) (Table 3).

The mean weight of young males born in late January 1987 {n = 22) always
exceeded that of females (/; = 1 3 ); the difference became statistically significant
at day 126 (early June 1987; t = 2.4. P < 0.05). At this age males averaged
101.3 g heavier than females (Table 5).

The combined instantaneous growth rates (IGR) of young males and
females born in early March 1986 generally decreased with age: however,
there were some exceptions (Table 6). The combined IGR of young males and
females born in late January 1987 decreased with age (Table 7).

Table 5. Mean weights and tail lengths of young male and female Mexican prairie
dogs (cohort bom late January 1987) from mid-April 1987 to late January 1988. See
Table 1 for dates of sampling periods. (Sample size given in parentheses.)

Sampling
period

Mean weight (g)^

Young cTd"

Young 99

Mean tail length (mm)
Young dtr Young 99

20 343.2± 22.6 (9)

21 685.5± 45.0(10)

23 866.7+ 68.1(10)

24 815.3±144.2 (4)

320.4± 36.8 (5)
584.2+ 75.1 (5)
788.7±126.2(7)
719.0+147.2(4)

73.913.9 (9)
97.7+4.0(10)
99.5 + 3.0(10)
99.8±2.7 (4)

69.6+ 3.4(5)
92.6± 4.6(5)
92.3± 7.1(7)
94.3±1 1.5(4)

^ + 95% confidence limits

10 OCCASIONAL PAPERS

Table 6. Instantaneous growth rates of weights and tail lengths of young Mexican
prairie dogs (cohort born early March 1986) from mid- April 1986 to late September
1986 calculated using the technique of Brody (1945).

Rate (%)

Age (days) Young crcr& 99 Young cTcT Young 99

Weight

45-65

2.35

65-86

2.43

86-104

1.25

04-140

0.85

40-162

0.43

62-190

0.61

90-209

0.21

45-65

1.13

65-86

0.84

86-104

0.56

04-140

0.31

40-162

0.05

62-190

0.04

90-209

0.05

Tail length

2.15 2.55

2.38 2.48

1.44 1.05

0.86 0.83

0.59 0.27

0.57 0.64

0.16 0.26

1.10 1.15

0.81 0.84

0.61 0.50

0.36 0.25

0.05 0.05

0.04 0.04

0 0.10

Table 7. Instantaneous growth rates of weights and tail lengths of young Mexican
prairie dogs (cohort bom late January 1987) from mid-April 1987 to late January 1988
calculated using the technique of Brody (1945).

Rate (%)

Age (days) Young crcr& 99 Young cTd" Young 99

Weight

74-126 1.24 1.15

126-257 0.20 0.22

257-357 -0.08 -0.09

Tail length

74-126 0.58 0.58

126-257 0 0

257-357 0 0

1.33

0.18

-0.06

0.58

0

0

MEXICAN PRAIRIE DOG ANNUAL CYCLE 1 1

Yearlings

The minimum mean weight of yeading ( 1986 cohort) males and females
in 1986 occurred in mid-June, and the maximum occurred in late September,
indicating continuing growth during June, July, August, and September
(Table 8).

The minimum mean weight of yearling (1987 cohort) males occurred in
late January 1988, whereas the maximum mean was in late August 1987
(Table 9). The lowest mean weight of yearling ( 1 987 cohort ) females occuired
in early June 1987 and the maximum in late August 1987.

Sexual dimorphism of tail length was not significant at any date. Among
17 yearlings captured from mid- June to late September 1986, males were
heavier and had longer tails than females (Table 8). Among 12 yearlings
captured from mid- April 1987 to late January 1988, males were heavier and
had longer tails than females (Table 9).

Adults

The lowest mean weight of adult males occurred in mid-February 1986,
while the highest mean weight was found in late December 1986 (Table 10).
The minimum mean weight of adult females occurred in early May 1986 and
the maximum mean weight occurred in late January 1987 (Table 10).
Variation in mean weight of adults during this study reflects seasonal
variation, but because samples varied in size and individual composition,
similar trends were not always seen when trajectories of weight of individuals
caught in different capture periods were calculated (Table 1 1 ).

Tail lengths and weights of adult males and females differed significantly
(Table 12). Adult males hadlongertails than females during the study (Table

Table 8. Mean weights and tail lengths of yearling male and female Mexican prairie
dogs (cohort bom late May 1985) from mid-June 1986 to mid-April 1987. See Table
1 for dates of sampling periods. (Sample size given in parentheses.)

Sampling Mean weight (g)^ Mean tail length (mm)

period Yearling Cfcf Yearling 99 Yearling cScS Yearling 99

12 913.8± 48.0 (6) 843.0+196.0(2) 105.8±3.9 (6) 104.5±2.9(2)

13 980.0± 28.1 (5) 898.0± 58.8(5) 104.6±4.0 (5) 106.617.5(5)

14 1053.0± 82.1 (7) 956.3126.7(6) 106.1 + 2.7(7) 104.712.4(6)

15 1072.5178.7(10) 1005.0128.8(6) 104.812.6(10) 107.512.7(6)

16 1166.3+96.1(6) 1034.7138.0(6) 107.313.4(6) 105.013.7(6)
20 1093.01104.0(4) 981.3153.9(6) 108.011.8(4) 106.011.0(6)

''I 95% confidence limits

12 OCCASIONAL PAPERS

Table 9. Mean weights and tail lengths of yearling male and female Mexican prairie
dogs (cohort bom early March 1986) from mid- April 1987 to late January 1988. See
Table 1 for dates of sampling periods. (Sample size given in parentheses.)

Sampling Mean weight (g)'^ Mean tail length (mm)

period Yearling cTd" Yearling 99 Yearling Cfd" Yearling 99

20 1143.0± 98.0(3) 955.0+84.2(5) 108.1±1.7(3) 101.4±0.7(5)

21 1123.7± 89.0(3) 884.0±44.9(5) 108.0±1.7(3) 99.6±1.5(5)

22 1260.0 (1) 1060.0 (1) 108.0 (1) 103.0 (1)

23 1223.0±137.2(2) 1002.2±69.8(6) 106.5±1.5(2) 100.5± 1.5(6)

24 1064.0 (1) 929.0±42.7(3) 105.0 (3) 98.3±2.9(3)

''±95% confidence limits

10), and they were also heavier than females, except when females were
pregnant and in early lactation (for example, from mid-February to late March

1986 and late December 1986 to late February 1987).

Weight Variation

Yearling (1986 cohort) and adult weights did not differ significantly by
mid-June in females and late July in males. Yearling (1987 cohort) and adult
weights did not significantly differ by mid- April 1987. Mean weight of adult
males exceeded that of females during most of this investigation, the only
exceptions being from mid-February to late March 1986 and in late February

1987 (Table 11).

Patterns of Molt

There were two complete pelage renewals (winter and summer) and two
transition pelage periods (spring and autumn) from early October 1985 to late
September 1986.

Winter pelage, wom froin late September to mid-March, was characterized
by long, soft guard hairs. The spring transition pelage was characterized by
shedding of winter hairs and the appearance of short, coarse suminer hair in
an anterior-posterior direction. This pelage lasted from late March to late
May in most adults. However, in inost young born in late May 1985, the
transition pelage terminated in early May 1986. just before they became
yearlings (Table 13). During April 1986. the pelage of young that were born
in early March 1986 also could be considered transitional (Table 13). In these
young the renewal of pelage from winter to summer was in a posterior-
anterior pattern, instead of the anterior-posterior pattern seen in adults.

MEXICAN PRAIRIE DOG ANNUAL CYCLE

13

Table 10. Mean weights and tail lengths ot adult male and female Mexican prairie
dogs from mid-October 1 985 to late January 1 988. See Table 1 for dates of sampling
periods. (Sample size given in parentheses.)

Sampling Mean weight (g)^

Mean tail length (mm)

period Adult CfCf^ Adult 99

Adult CfcT Adult 99

1

918

2

951

3

938

4

934

5

913

6

824

7

926

8

898

9

948

10

895

11

936

12

976

13

1038

14

1065

15

1095

16

1151

17

1 303

18

1001

19

1143

20

1133

21

1089

22

1122

23

-1085

24

981

.0±

28.3

4)

.3±

16.3

3)

.0±

50.0

5)

.7±

43.2

3)

.0±

66.5

5)

.3±

32.9

5)

.4±

43.2

3)

.0+

59.7

5)

.0±

52.3

'5)

.0±

78.2

5)

.8±

23.5

4)

.8±

34.3

4)

.0±

82.3

4)

.0±

59.6

5)

.0+

94.8

5)

.3 +

26.7

4)

.0

1)

.0±

99.9

2)

.0

1)

.0±156.8

2)

.0±

51.4

5)

.0±

72.7

5)

.9 +

72.4

7)

.5±

73.5

.2)

851.3±

843.0±

830.5 ±

830.5±

836.8±

873.0±

947.2±

914.4±

838.8±

756.3 ±

775. 8±

797.0±

909.7±

931.3±

991.0±

1079.0±

1313.0

1343.0

1293.0±

1011.3±

956.6+

1082.0±

1 030.5 ±

894.0±

43.2

3)

00.0

2)

25.0

4)

17.7

2)

46.4

4)

50.0

5)

19.7

6)

34.5

7)

65.0

6)

70.7

6)

25.6

9)

15.8

.5)

40.8

'6)

35.2

6)

35.5

6)

58.4

5)

1)

1)

19.6

2)

[18.3

(6)

50.9 (

1)

83.0

(4)

69.7(1

0)

67.9

[3)

96.3 ±

8.8(

4)

96.7±

2.4

3)

95. 6 ±

7.1(

5)

99.3 +

2.0

3)

98.2±

8.3(

5)

101.8 +

6.1(

5)

105.4±

0.3

(3)

102.6±

6.5(

5)

102.6±

6.5

5)

102.6±

6.5(

5)

101.3 +

3.8(

4)

105.3 +

7.3

4)

106.0±

7.8

4)

104.8 +

6.6

5)

105.5± 6.1

5)

102.3 +

2.7

4)

101.0

(

1)

100.0+

1.0

2)

101.0

(

1)

103.0+

2.0

2)

107.2 +

2.6

5)

106.4±

2.4

5)

105.3 +

1.6

7)

101.5 +

0.5

2)

76.7 +
89.0+
95.5 ±
90.5 +
95.0+
95.4+

93.7 +
93.6+

97.8 +
97.2 +
97.6±
99.6+
98.8 +

100.5 +
100.5±

101.2 +
107.0
107.0
106.5 +
101.5 +

101.3 +
105.3 +
103.1 +
106.3 +

9.6
11.8
3.0
8.8
3.4
6.4
6.3
5.8
6.3
6.4
4.7
7.5
6.8
8.9
8.9
4.7

(3)
(2)
(4)
(2)
(4)
(5)
(6)
(7)
(6)
(6)
(9)
(5)
(6)
(6)
(6)
(5)
(1)

0.5 (2)
1.9 (6)
2.4(11)
0.6 (4)
2.4(10)
0.9 (3)

^ ± 95% confidence limits

''Adults and yearlings before April 1986; all adults thereafter

Summer pelage was characterized by short, coarse hair. Adults displayed
this pelage from early June to late August. Summer pelage was found in
yearlings from late May to late August. In young that were bom in early March
1986, summer pelage occurred from early May to late July (Table 13). The
summer-winter pelage transition was characterized by the appearance of
long, soft hair in an anterior-posterior direction in prairie dogs of all ages. The
transition period was brief, from early September to mid-September in adults
and yearlings, and from early August to mid-September in young (Table 13).

14 OCCASIONAL PAPERS

Table 1 1. Variation in weight of adult Mexican prairie dogs from mid-October 1985
to late January 1988. See Table 1 for dates of sampling periods.

Sampling

Adulters a

Adult 99 a

period

X,- ± 1 - X,- ''
33.0

25.0

«d

X,- ± 1 - X,

D

n

1

3

-8.3

25.0

1

2

-13.3

8.3

3

-12.5

0.0

1

3

-3.3

-25.0

3

0.0

0.0

1

4

-21.7

25.0

3

6.3

25.0

1

5

-88.7

-108.3

4

36.2

18.8

4

6

102.0

75.0

3

74.2

70.0

5

7

-28.3

8.3

3

-32.8

-125.0

6

8

50.0

50.0

5

-75.6

-65.0

5

9

-53.0

-53.0

5

-82.5

-109.0

5

10

41.8

41.3

4

19.5

31.7

6

11

40.0

28.3

3

21.2

28.3

3

12

61.2

61.3

4

112.7

111.0

5

13

27.0

67.5

4

21.6

31.0

5

14

30.0

30.0

5

59.7

52.0

6

15

56.3

55.8

4

88.0

57.5

4

16

151.7

7.0

1

239.0

225.0

1

17

-302.0

-200.0

2

30.0

30.0

1

18

143.0

40.0

1

-50.0

-60.0

2

19

-10.0

70.0

2

-281.7

-300.0

6

20

-44.0

-68.5

5

-54.7

-38.0

11

21

33.0

16.0

5

125.0

42.7

4

22

-36.1

-37.0

4

-51.5

-A1.3

10

23

-104.4

-156.5

2

-136.5

-164.7

3

^Adults and yearlings before April 1986; all adults thereafter

'^x, is the mean of the first sampling period, x, ± 1 is the mean of the second sampling

period
'^D is the mean of the differences in weight of individuals caught in both sampling

periods
"^n is the number of individuals used in calculating D

Disappearance Rates

Of 1 8 adult Mexican prairie dogs captured and marked from early October
1985 to late September 1986, 3 (17%) disappeared between early November
1985 and late March 1986, and 1 (6%) disappeared between early April 1986
and late September 1986. Among 20 marked young (bom in late May 1985),
6 (30%) disappeared by March 1986, and 1 (5%) disappeared between April
and late May 1986. Of 17 yearlings captured and marked as young, 1 (6%)

MEXICAN PRAIRIE DOG ANNUAL CYCLE

15

Table 12. Weight and tail-length characteristics of adult Mexican prairie dogs
from mid-April 1986 to late January 1988.

Measurement

Mean^

Range

SD

r-test''

Males (/; =

:61)

Tail length (mm)

104± 1.4

97-117

5.6

Total weight (g)

1045 ±28.3

Females {u

868-1303

= 87)

112.8

Tail length (mm)

101+ 1.6

85-109

7.4

4.49

Total weight (g)

943±31.5

758-1343

150.1

2.68

'^ ± 95% confidence limits
¥ < 0.05

disappeared between mid-June and September 1986. Of the 21 young (bom
in early March 1986), 3 (14%) had disappeared by late September 1986.

There were 3 1 observations of ferruginous hawks {Buteo regalis) on or
adjacent to the study site from early November 1 985 to late March 1986, and
some fed on prairie dogs. In late November 1 985, 1 observed five ferruginous
hawks fighting over the remains of one prairie dog on the study site. During
the winter months, I observed three captures and eight additional capture
attempts of prairie dogs by ferruginous hawks, but no marked prairie dog was
captured. Although red-tailed hawks {Buteo jamaicensis), golden eagles
{Aquila chrysaetos), and coyotes (Canis latrans) also were observed attempting
to capture C. mexicanus, ferruginous hawks were the main diurnal predator
during the winter. The disappearance of adult and yearling prairie dogs during
winter was probably due to predation, although undocumented emigration
may have accounted for some losses.

Activity and Social Organization

Mexican prairie dogs are strictly diurnal. Two periods of maximum above-
ground activity occurred daily at the study site from mid-spring to early fall
1986. The first started at approximately 0730 h and lasted until 1 230 h or 1 300
h, when air temperature reached its maximum (mean maximum = 28°C). The
second started at approximately 1500 h, as air temperature declined, and
continued until just before sunset. From late fall 1985 to early spring 1986,
Mexican prairie dogs showed only one daily period of maximum surface
activity, beginning at approximately 0900 h and lasting until sunset. All
above-ground activity stopped during rain; water standing on the ground

16

OCCASIONAL PAPERS

oc

ON

00

in

00

X)

o
o

o
-6

s

o

-a

a
o

c

o

C/3

C3
C

X

f2

00

o

c

00

g

C

00

'o

O

c

in

00

c

3

O

o

<

B

3
<

00

C/0

00

on
H

00

c/o

H

00

00
00

00
00

H

C

I -

CO

OOOOOin^OO
r<-, \D vO ON On ri O O
r) ^ — O O O O O
OOOOOOOON

O O O O O ir, \0 O
' — ^^NOOONr<"jOO

^'i-riooooo

ooooooor-

OOOOOOOOOOOOOO — nOO
OOOOOOOOO — — ^riinir, OO
oooooooo^voinriooooo
— irir^oo^oor~\D ri oooooooi/~i

oooooooooooooo — oo

OOOOOOOOOOO-tr-ir. ^oo
OOOOOO — — "^r-r-rr, ooooo
r<-, r^oooo-^oovovor-toooooooo

oooooooooooooo — ^o

OOOOOOOOOOO — '^. NOinriO

oooooooninvCNOocrjocoo
o r<-j (^1 ^ ri ""t i/~j 1^^. — ^ o o o o o o o in

OOOOOOOOOOOOOOOr<-. O
OOOOOOOOOO — ni~^. 'tmi — o

oooooooo"^in^r<-, ^-oooo

ri -t i~^. in r<-, ly-, U", r^j — O O O O O O — m^

in in ir-, in in vo \c vo ^ vO ^ nO vc o vo NO ^

OOOOOCOOOO^OOOOaOOCOCOCOOOOOOOOOO'OC

D.

C

?3

c

I

P

o o o o

«J ^ "S ^ ^ 5-^ ^ 3 3 5 at oT

6ozzQ^£SS<SS

< c/5 oo

rnoot^r^ON(Nir, r-NONONONO-^O — ^oor~-
— ri — n — ri — ri — ri — ri

OJ
OXJ

i2

!U

D.
;-
(U

E
S

3

C/3
II

C/0
(J

. Ofj

a D.

;- C

1) o

« t.

. , !U

NO P

00 ^

On C

— 3

. c/3

■g ^

< C

o ^

X oo

•y. H

&[) -

"O (L)

3 II

< ^

MEXICAN PRAIRIE DOG ANNUAL CYCLE 17

surface reduced but did not stop activities.

Tactile communication in C. mexicamis involved a "kiss" similar to that
described for black-tailed prairie dogs {Cynomys ludoyicianus)hy King ( 1 955 ).
The "kiss" occurred in young-mother and young-young relations. If an adult
Mexican prairie dog adopted the "alairn" posture (sitting up and peering
around), other prairie dogs in the immediate vicinity did likewise. Mexican
prairie dogs at the study site commonly used two distinctive calls that can be
termed an "alarm bark" and "elation call." Both calls were used by young,
yearling, and adult C. mexicamis. The olfactory stimulation described by
King (1955) for black-tailed prairie dogs was not noted for C. mexicamis.

The 9.55 ha study site was initially occupied by five groups (coteries) of
prairie dogs; by late September 1 986, the site held six distinct groups. Groups
usually consisted of one or two adult males and one to four adult females,
similar numbers of both yearling males and females, and young of the year
(Table 14). Dominance behavior was difficult to identify; however, when it
occurred it was exhibited by a single reproductive male toward the entire
social group. Following the breeding season, behavioral antagonism was
observed within the groups. Adult females did not permit adult males in or
near the nesting bunow. This agonistic behavior ended with the emergence of
young in mid- April 1986. Young were very sociable within their groups, but
they rarely approached group boundaries. By early June movements of adult
and yearling prairie dogs between groups within the colony were evident;
these movements lasted until early September 1986. One movement of
particular interest occurred in early June 1986; a yearling male moved away
from its original group (I) to another group (IV) dominated by an adult male.
During a period of 15 days, the yearling male succeeded in displacing the
adult male from its original group to another site, where the adult established
a new group (VI) with an adult female, a yearling male, and a yearling female.
Intergroup movements involved not only single prairie dogs, but also groups
of prairie dogs. In early June 1986, three yearling males and two adult males
simultaneously moved away from their original group (III) to join another
group (V) consisting of two adult females, one yearling male, and two
yearling females. Apparently movement of both individuals and groups of
prairie dogs occurs when they reach adult size; this coincides with the
suggestion of AiTnitage (1981) that sexual maturity and dispersal in large-
bodied social ground squirrels are dependent on the age at which immatures
attain adult weight.

DISCUSSION

Reproduction

Since 1892, only three reports on reproduction in Cynomys mexicamis
have been published (Merriam, 1892; Baker, 1956; Pizzimenti and

18 OCCASIONAL PAPERS

Table 14. Group composition of Mexican prairie dog colony by age and sex.

Group

Adult^

Yearling

Unmarked

Young

Unmarked

Total

no.

cf

9

cf

9

adult-young

CT

9

yearlings

October-December 1985

I

1

1

—

5

2

2

11

n

1

1

—

2

2

3

—

9

m

2

0

—

—

3

4

1

10

rv

2

2

—

1

1

2

8

V

0

1

5

0

0

6

VI

0

0

—

0

0

0

0

Total

6

5

—

16

9

8

—

44

January-March 1986

I

2

3

2

2

2

11

n

1

1

—

2

2

2

—

8

III

2

0

—

2

4

2

10

IV

1

1

—

1

0

2

5

V

0

2

—

1

1

2

6

VI

0

0

—

0

0

0

0

Total

6

7

"

8

9

10

40

Group

Adult
tf 9

Yearling
cf 9

Unmarked ^
adult-yearling

foun

g'86

Unmarked
young '86

Total

no.

Cf

9

April-May 1986

I

2

4

2

1

1

6

7

3

26

II

1

1

1

2

2

1

2

1

11

m

2

0

4

1

2

0

0

0

9

IV

1

1

0

2

1

2

2

0

9

V

0

2

1

2

4

0

0

0

9

VI

0

0

0

0

0

0

0

0

0

Total

6

8

8

8

10

9

11

4

63

June-September 1986

I

2

4

1

1

0

5

7

3

23

II

1

0

0

2

0

1

2

1

7

III

0

0

2

2

0

0

0

0

4

IV

0

1

2

2

0

T

2

0

9

V

1

2

4

1

0

0

1

3

12

VI

1

1

1

1

0

0

0

0

4

Total

5

8

10

9

0

8

12

7

59

^Adults and yearlings before April 1986; all adults thereafter

MEXICAN PRAIRIE DOG ANNUAL CYCLE 19

McClenaghan, 1974). Typically one litter is produced annually in the genus
Cynomys (Clark et al., 1971; Pizzimenti and Hoffmann, 1973). However,
Pizzimenti and McClenaghan (1974) suggested that Mexican prairie dogs
may reproduce more than once each year, or alternatively that the reproductive
season is extremely protracted. Ceballos-G. and Wilson (1985) mentioned
that the length of gestation is unknown, but suggested it may be about one
month as in other Cynomys. Van De Graaff and Balda ( 1 973 ) noted that green
vegetation in the diet contributed to increased body vigor in Merriam's
kangaroo rat {Dipodomys mciriami) and provided the extra energy required
for reproduction. Reynolds and Turkowski (1972) found that for each
additional 0.50 in. of December-January rainfall, initiation of the breeding
season in round-tailed ground squirrels (Spennophilus tereticaudus) was ad-
vanced about 9 days. Conversely, low rainfall during winter delayed the
breeding season. Koford ( 1958) reported that the breeding season in black-
tailed prairie dogs (Cynomys ludovicianus) did not change from one dog town
to another despite differences in food and weather. He concluded that the time
of breeding was not determined by food, and thought that the determining
factor might be day length. Anthony and Foreman ( 195 1 ) found that light,
darkness, and cold did not change the timing of the reproductive cycle in
female black-tailed prairie dogs.

Although Zones I and II are in close proximity, the rainfall pattern is quite
different between the two, with Zone I averaging more precipitation. The
rainfall in Zone I was more uniformly distributed throughout the year. In Zone
I, the highest biomass of green vegetation was recorded in December 1985;
the highest biomass in Zone II was during the period May through July and
averaged twice that found in Zone I. Because winters at Ejido El Tokio are
mild, increased food availability during the late winter-early spring season is
probably the stimulus that initiates reproduction in C. mexicauus. Therefore,
it seems that differences in timing of breeding between Zone I and Zone II
were due to differences in timing of food availability, which in turn results
from differences in rainfall patterns. This hypothesis is supported by the
capture of young prairie dogs in October 1985 and in April 1987 on the study
site. Young prairie dogs captured in October 1985 were bom in May. Delayed
reproduction in 1 985 can be attributed to the low rainfall on the study site from
December 1984 to March 1985(Treviiio-Villarreal, 1988). Presumably green
vegetation was scarce until April 1985. In contrast, young prairie dogs
captured in April 1987 were bom by late January. Early reproduction in 1987
can be linked to the high rainfall on the study site from October 1986 to
January 1 987; green vegetation probably was abundant in these months. Mild
climatic conditions in the range of Mexican prairie dogs permit a longer
reproductive season than in the other species oiCynomys, which either hibernate
or are inactive much or all of the winter (Longhurst, 1944; Scheffer, 1947;
King, 1955; Bakko and Brown, 1967; Rayoretal., 1987). Adult and yearling

20 OCCASIONAL PAPERS

females produced a single annual litter both on the study site and nearby. No
pregnant yearling female was found from early October 1 985 to late September
1986. On the other hand, all yearling females were lactating when they were
captured in mid-April 1987. These results contradict the speculation by
Pizzimenti and McClenaghan (1974) that breeding in Mexican prairie dogs
might occur more than once each year.

Average litter size in Cynomys leucurus varies from 4.9 to 5.6 (Clark et al.,
1971). A female C. mexicanus with three embryos was found on 4 March
(Merriam, 1892) and another taken on 25 March contained three embryos
averaging 23 mm in crown-rump length (Baker, 1956). On 26 May, five
months after capture, one of two adult females housed with an adult male
produced a litter of four males and two females (Pizzimenti and McClenaghan,
1974). Mean litter size increases with better nutrition in round-tailed ground
squirrels {Spermophilus tereticaudus) (Reynolds andTurkowski, 1972). The
present study covered two reproductive seasons (1986 and 1987) at one
locality; therefore, it was only possible to deteimine that mean litter size of
C. mexicanus varied from one year to another. The mean litter size in 1986
(4.0) differed from the mean litter size in 1 987 (4.5 ) {t = 2.6, P < 0.05 ) (Table
2). This litter size difference may have been due to increased precipitation in
fall and winter of 1986 in Zone I, which in turn increased food availability.

Emergence of young on the study site and in Zone II in 1 986 coincided with
the appearance of summer annuals, which provided food for early growth.
Yearling Mexican prairie dogs did not exhibit evidence of reproductive
maturity in 1986. Neither sex had achieved full seasonal adult weight by the
time copulation occurred in late January and early February 1986. Young
Mexican prairie dogs (bom in early March 1986) approached minimum
seasonal adult weight by early September 1986 (Table 3). Thus, on the basis
of weight, Cynomys mexicanus could be capable of reproduction either in its
first year or in its second year of life. Whether reproduction by yearlings or
young ever occurs probably depends upon food availability and social
interactions.

Size and Growth

Ceballos-G. and Wilson (1985) reported that weaning of C mexicanus
occurs between 41 and 50 days. The calculated age of young at first capture
was 45 days in 1986 and 74 days in 1987 on the study site. Growth and
development differed between the young studied by Pizzimenti and
McClenaghan (1974) and the young studied in the two reproductive seasons
in this study. For instance, Pizzimenti and McClenaghan ( 1974) found that the
mean weight of C. mexicanus exceeded 1000 g by 19 weeks, whereas mean
weight of free-ranging C. mexicanus was 925.1 g (SD = 94.56, /; = 14) at 30
weeks of age. Pizzimenti and McClenaghan (1974) also stated that sexual
dimorphism in weight of young was significant at 60 days (t = 4.5. P < 0.02)

MEXICAN PRAIRIE DOG ANNUAL CYCLE 21

and in tail length at 42 days {r = 3.6, P < 0.05). In 1986, significant weight
{t = 2.3, P < 0.05 ) and tail-length dimoiphism {r = 3.8, P<0.0\) between the
sexes occurred at 140 days, whereas in 1987 significant weight dimoiphism
(t-2.4,P < 0.05 ) between the sexes occurred at day 1 26. No significant tail-
length dimoiphism between the sexes occurred in these young throughout this
study. Pizzimenti and McClenaghan (1974) found that at 140 days males
averaged 293 g heavier than females. At this age males bom in 1986 averaged
only 69.4 g heavier than females. Young males born in 1987 averaged 101 .3
g heavier than females at 1 26 days of age. The higher mean weight differences
in the captive litter (Pizzimenti and McClenaghan. 1974) than in wild young
from both 1 986 and 1987 may have been due to higher nutritive value of food
provided to and lower energetic demands on the captive litter. Mean weight
differences between the young from 1986 and 1987 probably resulted from
differences in food availability in 1986 and 1987 on the study site. An
alternative hypothesis is that the young were the same age at first capture in
both years, but that food availability and, therefore, growth rate were higher
in 1987.

Weight Variation

The weights of 29 adult C. mexicamis recorded from museum specimens
indicated that males were heavier than females (Pizzimenti and McClenaghan,
1974). Mean weight of adult males exceeded that of females during most of
this investigation, the only exceptions being from mid-February to late March
1986 and in late February 1987. The period of pregnancy in 1986 occurred
from mid-February to late March; in this period, adult females gained weight
rapidly. Adult females also had high mean weights during the period of early
pregnancy in 1987. which occurred in late February. The minimum mean
weight of adult males occurred in mid-February 1986, probably due to
decreased food availability (Treviiio-Villarreal, 1988). The consistent weight
gain by males from May to late September 1986 was associated with the
seasonal maximum in standing crop of green vegetation (Treviiio-Villarreal,
1988). The minimum mean weight of adult females occurred in early May
1986, subsequent to parturition and lactation. After young were weaned,
females began to regain weight.

Dalquest ( 1 953 ) noted that specimens taken in late September were fat and
suggested that they might be preparing for hibernation: however, Ceballos-
G. and Wilson (1985) believed that Mexican prairie dogs had no period of
inactivity or hibernation in the winter. The high mean weight of all age classes
of Mexican prairie dogs in late September 1986 should not be interpreted as
preparation for hibernation, as Dalquest (1953) suggested. All individuals of
Cynomys mexicanus were active throughout the study period, and they
achieved peak mean weight in late September 1986 because food availability
was high on the study site prior to that time (Treviiio-Villarreal. 1988).

22 OCCASIONAL PAPERS

However, all adult males, yearlings, and young lost weight from October
1987 to March 1988, but not in the winter of 1985-1986. Thus, stored fat may
be used in those winters when food is inadequate to sustain growth and
maintenance. In this regard, C. mexicanus is more similar to C. liidovicianus
than to C. leucurus or C. gunnisoni.

Patterns of Molt

Although the molting pattern has not been described in detail for Cynomys
mexicanus, it was reported to be complex (Ceballos-G. and Wilson, 1985).
Hollister (1916) declared that molting in C. mexicanus differed from other
species of prairie dogs in that the coat is irregularly and patchily renewed
rather than renewed in a regular anterior-posterior fashion, and that two or
possibly three complete pelage renewals occur annually in adults (Hollister,
1916; Baker, 1956). Molting in C. mexicanus pups also may be complex,
involving four or more overlapping phases and, as in adult molt, may be a
unique pattern for the genus (Pizzimenti and McClenaghan, 1974). In the
present study, molting of adult and yearling C. mexicanus occurred in an
anterior-posterior pattern. In contrast, young prairie dogs exhibited a posterior-
anterior pattern in their first pelage renewal in summer, but the second pelage
renewal in autumn occuned in an anterior-posterior pattern. This pattern
differs from the inegular, patchy pattern reported by Pizzimenti and
McClenaghan (1974), which may reflect abnormal conditions in captive
animals.

Disappearance Rates

Kit foxes {Vulpes macrotis) are effective predators on C. mexicanus
(Jimenez-Guzman, 1976). Likely additional predators are badgers (Taxidea
taxus), coyotes, long-tailed weasels (Mustela frenata), golden eagles, red-
tailed hawks, and rattlesnakes {Crotalus sp.) (Ceballos-G. and Wilson, 1985 ).
The high disappearance rate of adult and young prairie dogs from October
1985 to March 1986 probably was due to predation primarily by ferruginous
hawks {Buteo regalis). However, other causes and/or emigration of prairie
dogs cannot be ruled out. From early April 1986 to late September 1986, the
disappearance rate of prairie dogs was lower than from October 1985 to
March 1986. Individuals that disappeared probably were emigrants. During
this period some prairie dogs moved from one group to another within the
colony. Moreover, fewer diurnal predators were observed on the study site,
although nocturnal predators could have been significant. Lopez-Soto ( 1 980)
found remains of C. mexicanus in 1 3 of 40 scats of badgers, while Vallejo-
Gamero (1981) found a young C. mexicanus in the stomach of a rattlesnake
{Crotalus scutulatus scutulatus). Both badgers and rattlesnakes occurred near

MEXICAN PRAIRIE DOG ANNUAL CYCLE 23

the study site, but badger or rattlesnake activity were not observed on the
study site throughout the year.

Activity and Social Organization

Adult and yearling Mexican prairie dogs spent much of their day during
the summer months in behaviors concerned with social integration of the
groups.

The "identification kiss" ( King. 1 955 ) was used by C. mexicanus for recog-
nition and seems to play a major role in social organization. The alarm bark
of C. mexicanus is a single-syllable, repetitious bark. This call functions as an
"alert" to danger (Pizzimenti and McClenaghan, 1974). In the "elation call,"
the body may be thrown back on the first syllable, then downward onto the
forefeet on the second syllable (Pizzimenti and McClenaghan. 1974). This
"elation call" could be inteipreted as an "all-clear" signal as Waring (1970)
stated in his work on C. ludoviciamis. Other sounds made by Mexican prairie
dogs in the colony, and by animals marked and handled, included growls and
screams. Young, while playing or being handled, and adults and yearlings,
when confined in traps or handled, uttered both sounds.

Behavior of C mexicanus during the reproductive season seems to be
similar to other members of the genus Cynomys. Female C. ludovicianus
become territorial and aggressive around the parturition bunow during
gestation and lactation and do not resume social contacts with other members
of the colony until young are weaned and above ground (King. 1955). Female
C. gunnisoni also are more territorial during the reproductive season (Longhurst,
1944). Female Richardson's ground squirrels {Spermophilus richardsonii)
show similar aggressive behavior and teiritoriality during the reproductive
season (Clark, 1970). Coteries of black-tailed prairie dogs (King, 1955),
Gunnison's prairie dogs (C gunnisoni) (Rayor, 1988). and Mexican prairie
dogs (this study ) are typically composed of one or two adult males, one to four
females, and a variable number of young and yearlings.

All the species of the genus Cynomys are diurnal (this study; Tileston and
Lechleitner, 1966; Clark et al., 1971; Pizzimenti and Hoffmann, 1973;
Pizzimenti and Collier, 1975). Only C. mexicanus (this study) and C. ludo-
vicianus (Tileston and Lechleitner, 1966) are active throughout the year.
Bimodal and unimodal daily activity periods occur annually in C. mexicanus
(this study), C. ludovicianus (Tileston and Lechleitner, 1 966), and C. leucurus
(Clark et al., 1971). Bimodal daily activity periods occur in C. mexicanus
from mid-spring to early fall, in C. ludovicianus during the summer, and in C.
leucurus in mid-summer. A unimodal daily activity period occurs in C. mex-
icanus from mid-fall to early spring, in southern populations of C. ludovicianus
during the winter, and in C. leucurus from February to April and again from
September to November. Observed differences between the species in daily

24 OCCASIONAL PAPERS

activity periods are probably the result of the far less harsh climate in which
C. mexicanus lives, compared to C. ludovicianus and C. leiicwus on the Great
Plains or valleys of the intermountain West.

ACKNOWLEDGMENTS

I appreciate the hospitality of the people of Ejido El Tokio, Galeana, Nuevo
Leon, Mexico, who generously permitted me to carry out this study on their
land. I want to express my most sincere gratitude to the following persons: to
Robert S. Hoffmann, from whom I gained valuable knowledge during my
studies at The University of Kansas, and for his guidance and review of the
present study; to Kenneth B. Armitage. Barbara L. Clauson. Thorval Holmes,
Norman A. Slade, and Robert M. Timm for their critical comments on the
manuscript; to Robert R. Patterson who assisted me in obtaining equipment;
to Linda S. Rayor for her useful suggestions at the start of my fieldwork; to
Martha Laura Avalos-Marin who provided me with important information
from her thesis on percent vegetative cover and productivity; to my colleagues
Biol. Gustavo Arnaud-Franco, Biol. David Mercado, and Biol. Miguel A.
Zuiiiga; to my nephews Agustin, Jorge, Jose Gerardo. and Alejandro; to the
nicest woman in the world. Lie. Silvia Diaz Gonzalez, who helped me in the
field; to my star assistants Quique. Paco. Pepe, Julio, Genarin, Javier, Felipe,
and Carlingas for their help in trapping throughout the study; and to the many
other people who in one way or another helped me to finish this study, my most
sincere gratitude.

I am grateful to the Museum of Natural History, The University of Kansas,
for use of facilities and equipment. Anne M. Musser provided the final draft
of Fig. 2.

SUMMARY

Biological characteristics of Mexican prairie dogs {Cynomys mexicanus),
including reproduction, growth, development, molt pattern, and colony
organization were studied at Ejido El Tokio, Galeana, Nuevo Leon, Mexico,
from October 1 985 to January 1 988. The reproductive season was lengthy and
varied from one locality to another, as well as from year to year, depending
upon food availability. Females produced only one litter annually. Growth
rates in this study of free-ranging animals were lower than those reported for
captives by Pizzimenti and McClenaghan (1974). The molt pattern consisted
of two complete pelage renewals and two transition pelage periods annually.
Individual prairie dogs disappeared from the study site due to both mortality
and emigration. Mexican prairie dogs remained active above ground throughout

MEXICAN PRAIRIE DOG ANNUAL CYCLE 25

the year, and were strictly diurnal Bimodal daily activity periods occurred
annually from mid-spring to early fall. Unimodal daily activity patterns
occurred annually from mid-fall to early spring. Prairie dogs within the
colony were organized into groups (coteries) consisting of one or two adult
males, one to four adult females, and a variable number of young and
yearlings. After prairie dogs reached adult size, individual movements were
pronounced.

RESUMEN

Se examinaron algunas caracteristicas biologicas (reproduccion.
crecimiento, desarrollo, patron de muda de pelo, y organizacion colonial) de
los perritos mexicanos de las praderas (Cynomys mexicanus) en el Ejido El
Tokio. Galeana, Nuevo Leon. Mexico, desde Octubre de 1 985 hasta Enero de
1988. El periodo reproductive fue prolongado y vario de una localidad a otra,
asi como tambien de aiio con afio dependiendo de la disponibilidad de
alimento. Las hembras tuvieron solo una camada por aiio. Las tasas de
crecimiento en este estudio de animales silvestres fueron mas bajas que las
reportadas por Pizzimenti y McClenaghan ( 1 974 ) para animales en cautiverio.
El patron de muda consistio de dos cambios completes de pelaje y los
periodos de transicion del mismo por afio. La desaparicion de los perritos de
las praderas del area de estudio fue debido tanto a mortalidad como a
emigracion. Los perritos mexicanos de las praderas permanecieron activos
sobre la superficie durante todo el aiio, y fueron estrictamente diurnos. Los
periodos de actividad diaria bimodal ocurrieron anualmente desde mediados
de la primavera hasta principios del otoiio; mientras que los periodos de
actividad unimodal tambien ocurrieron anualmente, pero en este caso
ocurrieron desde mediados del otoiio hasta principios de la primavera. Los
perritos de las praderas estuvieron organizados dentro de la colonia en grupos
(coteries ) los cuales consistieron de uno o dos machos adultos, de una a cuatro
hembras. y un niimero variable de subadultos e infantiles. Los desplazamientos
individuales de los perritos de las praderas fueron pronunciados despues de
que alcanzaron la talla de adultos.

LITERATURE CITED

Anthony, A. and D. Foreman. 1951. Observations of the reproductive cycle of the
black-tailed prairie dog (Cynomys hidovicianus). Physiol. Zool. 24:242-248.

Armitage, K. B. 1981. Sociality as a life-history tactic of ground squirrels. Oecologia
48:36^9.

Avalos-Marin, M. L. B. A. thesis in prep: Productividad y bromatologia del pastizal
gipsofilo del Ejido El Tokio, Galeana. Nuevo Leon, Mexico. Universidad

26 OCCASIONAL PAPERS

Autonoma de Nuevo Leon, Monterrey, Nuevo Leon, Mexico.
Baker, R. H. 1956. Mammals of Coahuila, Mexico. Univ. Kansas Pub. Mus. Nat. Hist.

9:125-335.
Bakko. E. B. and L. N. Brown. 1 967. Breeding biology of the white-tailed prairie dog,

Cynoniys leucurus. in Wyoming. J. Mamm. 48:100-112.
Brody, S. 1945. Time relations of growth of individuals and populations, pp. 484-574.

In: S. Brody (ed.), Bioenergetics and Growth. Reinhold, New York.
Ceballos-G., G. and D. E. Wilson. 1985. Cynoniys mexicamis. Mamm. Species

248:1-3.
Clark, T. W. 1970. Richardson's ground squirrel (Spermophihis richardsonii) in the

Laramie Basin, Wyoming. Great Basin Nat. 30:55-70.
Clark, T. W., R. S. Hoffmann, and C. F. Nadler. 1971. Cynoniys leucurus. Mamm.

Species 7:1^.
Dalquest, W. W. 1953. Mammals of the Mexican state of San Luis Potosi. Louisiana

State Univ. Studies, Biol. Ser. 1:1-229.
DETENAL. 1975. Direccion de Estudios del Territorio Nacional. Carta G14 C66

Edafologica y uso del suelo. San Jose de Raices. Escala 1 :50,000.
FiTZWATER, W. D. 1943. Color marking of mammals with special reference to squirrels.

J.Wildl.Mgt. 7:190-192.
Garcia, E. 1 973. Modificaciones al sistema de clasificacion climatica de Koppen, Ed.

U.N. A.M., Mexico.
Hall, E. R. 198 1 . The Mammals of North America, 2nded. John Wiley & Sons, New

York. 1:1-600 + 90.
Hollister, N. 1916. a systematic account of the prairie dogs. N. Amer. Fauna

40:1-37.
Jimenez-Guzman, A. 1976. Los perros de la pradera {Cynoniys niexicanus Merriam) y

su influencia en la agricultura en Nuevo Leon, Mexico. Fac. de Ciencias

Biologicas, Universidad Autonoma de Nuevo Leon, Monterrey, Nuevo Leon,

Mexico. Pp. 567-574.
King, J. A. 1955. Social behavior, social organization and population dynamics in a

black-tailed prairie dog town in the Black Hills of South Dakota. Contrib. Lab.

Vertebrate Biol. Univ. Mich. 67:1-123.
Koford, C. B. 1958. Prairie dogs, white-faces and blue gramma. Wild. Monogr.

3:1-78.
LoNGHURST, W. 1944. Observations on the ecology of the Gunnison prairie dog in

Colorado. J. Mamm. 25:24-36.
LoPEZ-SoTO, J. H. 1980. B. A. thesis: Datos ecologicos del tlalcoyote Taxidea taxiis

berlandieri en el Ejido El Tokio, Galeana, Nuevo Leon, Mexico. Universidad

Autonoma de Nuevo Leon, Monterrey, Nuevo Leon, Mexico. 34 pp.
Merriam, C. H. 1892. Description of a new prairie dog (Cynoniys mexicanus) from

Mexico. Proc. Biol. Soc. Washington 7:157-158.
Mulleried, F. K. 1 944. Geologi'a del estado de Nuevo Leon. Anal. Inst. Invest. Cientif.

U.N.L. l(2)Mty. Pp. 55-63.
Nowak,R.M.andJ.L.Paradiso. 1983. Walker's Mammals of the World, 4th ed.. Vols.

1, 2. The Johns Hopkins Univ. Press, Baltimore, Maryland. Pp. 1-1362.
Pizzimenti, J. J. and G. D. Collier. 1975. Cynoniys parvidcns. Mamm. Species

52:1-3.
Pizzimenti, J. J. and R. S. Hoffmann. 1973. Cynomys '^nnmsoiii. Mamm. Species 25: 1^.

MEXICAN PRAIRIE DOG ANNUAL CYCLE 27

PizziMENTi. J. J. AND L. R. McClenaghan, Jr. 1974. Reproduction, growth and

development, and behavior in the Mexican prairie dog Cynomys mexicanus

(Merriam). Amer. Midi. Nat. 92:130-14.S.
Rayor. L. S. 1 985. Effects of habitat quality on growth, age of first reproduction, and

dispersal in Gunnison's prairie dogs (Cynomys guiinisoni). Can. J. Zool.

63:2835-2840.
Rayor, L. S. 1988. Social organization and space-use in Gunnison's prairie dog.

Behav. Ecol. Sociobiol. 22:69-78.
Rayor, L. S., A. K. Brody. and C. Gilbert. 1 987. Hibernation in the Gunnison's prairie

dog. J. Mamm. 68:147-150.
Reynolds, H. G. and F. Turkowskl 1 972. Reproductive variations in the round-tailed

ground squirrel as related to winter rainfall. J. Mamm. 53:893-898.
Scheffer, T. H. 1947. Ecological comparisons of the plains prairie dog and the Zuni

species. Trans. Kans. Acad. Sci. 49:401—406.
SPR 198 1 . Secretaria de Programacion y Presupuesto. Sintesis Geografica de Nuevo

Leon, Anexo Cartografico: Carta estatal (climas).
Tileston, J. V. and R. R. Lechleitner. 1966. Some comparisons of the black-tailed

and white-tailed prairie dogs in north-central Colorado. Amer. Midi. Nat.

75:292-316.
Trevino-Villarreal, J. 1981. B. A. thesis: Datos ecologicos de la ardilla de tierra

Spermophilus spilosoma pallescens Howell (1928), en el Ejido El Tokio,

Galeana, Nuevo Leon, Mexico. Universidad Autonoma de Nuevo Leon,

Monterrey, Nuevo Leon, Mexico. 42 pp.
Trevino-Villarreal, J. 1988. M. A. thesis: The annual cycle of the Mexican

prairie dog {Cynomys mexicanus Merriam, 1892). Univ. Kansas, Lawrence,

Kansas. 35 pp.
Vallejo-Gamero, J. L. 1981. B. A. thesis: Taxonomia y distribucion de la famila

Crotalidae en el estado de Nuevo Leon, Mexico. Universidad Autonoma de

Nuevo Leon, Monterrey, Nuevo Leon, Mexico. 49 pp.
Van De Graaff, K. M. and R. P. Balda. 1973. Importance of green vegetation for

reproduction in the kangaroo rat, Dipodomys merriami merriami. J. Mamm.

54:509-512.
Waring, G. H. 1970. Sound communication of black-tailed, white-tailed, and

Gunnison's prairie dogs. Amer. Midi. Nat. 83:167-185.

UNIVERSITY OF KANSAS

MUSEUM OF NATURAL HISTORY

PUBLICATIONS

The University of Kansas Publications, Museum of Natural History,
beginning with volume 1 in 1946, was discontinued with volume 20 in
1971. Shorter research papers formerly published in the above series are
now published as The University of Kansas Museum of Natural History
Occasional Papers. The University of Kansas Museum of Natural
History Miscellaneous Publications began with number 1 in 1946.
Longer research papers are published in that series. Monographs of the
Museum of Natural History were initiated in 1970. Authors should
contact the managing editor regarding style and submission procedures
before manuscript submission. All manuscripts are subjected to critical
review by intra- and extramural specialists: final acceptance is at the
discretion of the Director.

This publication is printed on acid-free paper. Occasional Papers and
Miscellaneous Publications are typeset using Microsoft® Word and Aldus
PageMaker® on a Macintosh computer.

Institutional libraries interested in exchanging publications may obtain
the Occasional Papers and Miscellaneous Publications by addressing the
Exchange Librarian, The University of Kansas Library, Lawrence,
Kansas 66045-2800, USA. Individuals may purchase separate numbers
from the Office of Publications, Museum of Natural History, The
University of Kansas, Lawrence, Kansas 66045-2454, USA.

Editor. Robert D. Holt

Managing Editor: Joseph T. Collins

Design and Typesetting: Kate Shaw and Joseph T. Collins

Printed by

University of Kansas Printing Service
Lawrence, Kansas

DATE DUE

'MAR 3-11996

DEMCO. INC 38-2931

3 2044 093 361 707