Chapter II: Part 2

Although females of _M. ochrogaster_ are much less precocious in their manifestations of puberty, they may become perforate well before impregnation can occur, and seem to pass through sterile cycles before becoming pregnant. The 18 smallest females recognized as being pregnant were of the following over-all lengths, in mm.: 149, 149, 149, 148, 148, 148, 147, 146, 145, 145, 144, 144, 143, 143, 143, 142, 135, and 134. As pregnancy is ordinarily recognized only in the last four days the females must have been impregnated from 20 to 17 days earlier--when they were in most instances 7 to 11 weeks old and 135 to 145 mm. in length. The two smallest individuals, recorded as pregnant at 135 and 134 mm., must, if they were of typical size for their age, have become pregnant at an age of approximately one month, when they were only 119 and 122 mm. in length. The smallest lactating females (some of them pregnant also) were recorded at lengths of 149, 148, 148, 147, 147, 146, 144, 144, 143, 143, and 142 mm. Occasionally females of less than 120 mm. were found to be perforate, and seemingly had begun oestral cycles. Records of a female of definitely known age, typical of many of the same size in her development, are cited below:

March 19, 1956 Born in captivity.

April 7, 1956 (19 days old) Released on study area at site of mother's capture; length 102 mm., weight 11.1 gms.

April 15, 1956 (27 days old) Recaptured; perforate with a copulatory plug; length 113 mm., weight 13.4 gms.

April 27, 1956 (39 days old) Recaptured; imperforate; length 131 mm., weight 24.3 gms.

May 12, 1956 (54 days old) Recaptured; perforate and in late pregnancy; length 146 mm.

May 25, 1956 (67 days old) Recaptured; imperforate, in an advanced state of lactation; length 150 mm., weight 33 gms.

When captured on May 12, at an age of 54 days, this female appeared to be within two or three days of parturition, and hence must have become pregnant at an age of approximately 35 or 36 days. Pregnancy in the more precocious females probably occurs at a length of approximately 130 mm. and an age of a little less than 40 days. Such females are still growing so rapidly that by the time their litters are born, they have grown to more than 140 mm.

GROWTH IN SUBADULTS AND ADULTS

Table 6 is a summarization of 73 records of individuals that made substantial growth as adults, after they were marked and measured. These records show the slowing trend of growth with advanced age. Also, they show the wide range of individual variation in growth rate, and difference between the sexes. With advanced age, growth in females lags behind that in males to an increasing extent. Exceptionally large individuals, of either sex, are many months old, but some individuals live to be a year old or more without growing much beyond average adult size. The average growth rate of more than 1 mm. per day in young has slowed to less than .1 mm. per day, on the average, in adults exceeding 160 mm., and has slowed to less than .05 mm. per day, on the average, in those exceeding 165 mm.

Table 6. Size Groups (Over-all Length) in Recaptured Voles That
Were Marked Before Maturity and Therefore Were of Approximately
Known Ages. ([M] = Male; [F] = Female)

===============+======================================+============
| Estimated age, in days |
Size Group +------------+------------+------------+ Number
Length in mm. | Average | Maximum | Minimum | in sample
---------------+------------+------------+------------+------------
171 to 175 | [M] 435 | ..... | ..... | 1
| [F] 324 | 338 | 310 | 2
| All 361 | 435 | 310 | 3
| | | |
166 to 170 | [M] 304 | 523 | 179 | 9
| [F] 398 | 597 | 158 | 6
| All 346 | 597 | 158 | 15
| | | |
161 to 165 | [M] 227 | 465 | 104 | 15
| [F] 257 | 394 | 134 | 18
| All 243 | 465 | 104 | 33
| | | |
156 to 160 | [M] 188 | 349 | 107 | 12
| [F] 187 | 284 | 93 | 11
| All 188 | 349 | 93 | 23
---------------+------------+------------+------------+------------

SUMMARY

The prairie vole is non-territorial and somewhat social. Several or many individuals of both sexes and various sizes may use the same system of surface runways and burrows and even the same nest. In general, members of such a group are mutually tolerant. A strange vole may provoke some hostility at first, but may soon be accepted as a member of a new group. Consequently, there are frequent shifts from one home base to another. Sexual relations are probably more or less promiscuous, although a male and female may rest and travel together in a semi-permanent association. In confinement only those males having markedly enlarged scrotal testes showed interest in females that were in oestrus. Post-partum females especially were eagerly pursued by such males. Anoestrus females are imperforate, and a vaginal orifice is present only during an active oestral cycle or in pregnancy. The perforate condition therefore, is a crude index of breeding activity in the population. In adult females the ratio of those that were perforate usually fluctuated between one-fourth and three-fourths of the total. Only in severe summer drought did the numbers decline below 24 per cent. Normally, breeding continues the year around, but it is temporarily inhibited in unusually cold weather or drought. The highest incidence of pregnancy normally is in late spring and early summer. The ratio of juveniles in the population from month to month and year to year is far more stable than the actual population density.

Gestation is 21 days or a little less. The mean litter is 3.37 +- .075 young. Three is the most frequent number per litter, with four, two, and five in that order of frequency. Larger and older females have more young per litter, on the average. Average size is greater in those litters having fewer young. At birth, young are between 40 and 50 mm. in length (typically, 47 mm.), and weigh 2.9 +- .05 grams.

At an age of nine days the young have their eyes open, and they may be weaned at an age of approximately three weeks. Young suckle chiefly from the four abdominal teats. The pectoral mammae seem to be inadequately developed, with the result that in exceptionally large litters of five, six or seven young, usually no more than four survive. Until weaning the young spend much of their time attached to the female's teats. She may even drag them behind as she forages. Females that have suckling young become much less tolerant of other voles. Attacks on young, and cannibalism, are common. Adult males, especially, are liable to eat the newborn young. The acquisition of cannibalistic habits by individuals, and seasonal lack of adequately nutritious plant foods may result in the killing off of young in such numbers that the population level is held down.

In young females sterile oestral cycles often begin at about the time of weaning. Earliest pregnancies occur when females are approximately one month old, but most are several weeks older before they become pregnant. Rate of growth declines steadily from a length increment of approximately 2 mm. per day in voles less than two weeks old to an increment of approximately one-fourth mm. per day in subadults. Growth rate is highly variable among individuals at all stages, and especially in those that have attained adult size. Even adults tend to gain in length, slowly, as well as in weight, and the largest individuals are all many months old.

LITERATURE CITED

BAILEY, V.

1924. Breeding, feeding and other life habits of meadow mice.
Jour. Agric. Res., 27: 523-536.

BODENHEIMER, F. S., and F. SULMAN.

1946. The estrous cycle of _Microtus guentheri_ D. and A. and
its ecological implications. Ecol., 27: 255-256.

GREENWALD, G. S.

1956. The reproductive cycle of the field mouse, _Microtus
californicus_. Jour. Mamm., 37: 213-222, 2 figs., 1 pl.

_Hamilton, W. J., Jr._

1941. The reproduction of the field mouse, _Microtus
pennsylvanicus_. Cornell Univ. Agric. Exp. Sta. Mem.,
237: 1-23.

HATFIELD, D. M.

1935. A natural history of _Microtus californicus_. Jour. Mamm.,
16: 261-271.

HOYTE, H. M. D.

1955. Observations on some small mammals of Arctic Norway. Jour.
Animal Ecology, 24: 412-425.

JAMESON, E. W.

1947. Natural history of the prairie vole. Univ. Kansas Mus.
Nat. Hist. Publ., 1: 125-151.

MARTIN, E. P.

1956. A population study of the prairie vole (_Microtus
ochrogaster_) in northeastern Kansas. Univ. Kansas Mus.
Nat. Hist. Publ., 8: 361-416.

SCHMIDT, F. J. W.

1931. Mammals of western Clark County, Wisconsin. Jour. Mamm.,
12: 99-117.

[]
26-7561

UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY

Institutional libraries interested in publications exchange may obtain this series by addressing the Exchange Librarian, University of Kansas Library, Lawrence, Kansas. Copies for individuals, persons working in a particular field of study, may be obtained by addressing instead the Museum of Natural History, University of Kansas, Lawrence, Kansas. There is no provision for sale of this series by the University Library which meets institutional requests, or by the Museum of Natural History which meets the requests of individuals. However, when individuals request copies from the Museum, 25 cents should be included, for each separate number that is 100 pages or more in length, for the purpose of defraying the costs of wrapping and mailing.

* An asterisk designates those numbers of which the Museum's
supply (not the Library's supply) is exhausted. Numbers
published to date, in this series, are as follows:

Vol. 1. Nos. 1-26 and index. Pp. 1-638, 1946-1950.

*Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest.
Pp. 1-444, 140 figures in text. April 9, 1948.

Vol. 3. *1. The avifauna of Micronesia, its origin, evolution,
and distribution. By Rollin H. Baker. Pp. 1-359,
16 figures in text. June 12, 1951.

*2. A quantitative study of the nocturnal migration of
birds. By George H. Lowery, Jr. Pp. 361-472, 47
figures in text. June 29, 1951.

3. Phylogeny of the waxwings and allied birds. By M. Dale
Arvey. Pp. 473-530, 49 figures in text, 13 tables.
October 10, 1951.

4. Birds from the state of Veracruz, Mexico. By George H.
Lowery, Jr. and Walter W. Dalquest. Pp. 531-649,
7 figures in text, 2 tables. October 10, 1951.

Index. Pp. 651-681.

*Vol. 4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466,
41 plates, 31 figures in text. December 27, 1951.

Vol. 5. 1. Preliminary survey of a Paleocene faunule from the
Angels Peak area, New Mexico. By Robert W. Wilson.
Pp. 1-11, 1 figure in text. February 24, 1951.

2. Two new moles (Genus Scalopus) from Mexico and Texas.
By Rollin H. Baker. Pp. 17-24. February 28, 1951.

3. Two new pocket gophers from Wyoming and Colorado. By
E. Raymond Hall and H. Gordon Montague. Pp. 25-32.
February 28, 1951.

4. Mammals obtained by Dr. Curt von Wedel from the barrier
beach of Tamaulipas, Mexico. By E. Raymond Hall. Pp.
33-47, 1 figure in text. October 1, 1951.

5. Comments on the taxonomy and geographic distribution of
some North American rabbits. By E. Raymond Hall and Keith
R. Kelson. Pp. 49-58, October 1, 1951.

6. Two new subspecies of Thomomys bottae from New Mexico
and Colorado. By Keith R. Kelson. Pp. 59-71, 1 figure in
text. October 1, 1951.

7. A new subspecies of Microtus montanus from Montana and
comments on Microtus canicaudus Miller. By E. Raymond
Hall and Keith R. Kelson. Pp. 73-79. October 1, 1951.

8. A new pocket gopher (Genus Thomomys) from eastern
Colorado. By E. Raymond Hall. Pp. 81-85. October 1, 1951.

9. Mammals taken along the Alaskan Highway. By Rollin H.
Baker. Pp. 87-117, 1 figure in text. November 28, 1951.

*10. A synopsis of the North American Lagomorpha. By E.
Raymond Hall. Pp. 119-202, 68 figures in text. December
15, 1951.

11. A new pocket mouse (Genus Perognathus) from Kansas. By E.
Lendell Cockrum. Pp. 203-206. December 15, 1951.

12. Mammals from Tamaulipas, Mexico. By Rollin H. Baker. Pp.
207-218. December 15, 1951.

13. A new pocket gopher (Genus Thomomys) from Wyoming and
Colorado. By E. Raymond Hall. Pp. 219-222. December 15,
1951.

14. A new name for the Mexican red bat. By E. Raymond Hall.
Pp. 223-226. December 15, 1951.

15. Taxonomic notes on Mexican bats of the Genus Rhogeessa.
By E. Raymond Hall. Pp. 227-232. April 10, 1952.

16. Comments on the taxonomy and geographic distribution of
some North American woodrats (Genus Neotoma). By Keith R.
Kelson. Pp. 233-242. April 10, 1952.

17. The subspecies of the Mexican red-bellied squirrel,
Sciurus aureogaster. By Keith R. Kelson. Pp. 243-250,
1 figure in text. April 10, 1952.

18. Geographic range of Peromyscus melanophrys, with
description of new subspecies. By Rollin H. Baker.
Pp. 251-258, 1 figure in text. May 10, 1952.

19. A new chipmunk (Genus Eutamias) from the Black Hills.
By John A. White. Pp. 259-262. April 10, 1952.

20. A new pinon mouse (Peromyscus truei) from Durango, Mexico.
By Robert B. Finley, Jr. Pp. 263-267. May 23, 1952.

21. An annotated checklist of Nebraskan bats. By Olin L. Webb
and J. Knox Jones, Jr. Pp. 269-279. May 31, 1952.

22. Geographic variation in red-backed mice (Genus
Clethrionomys) of the southern Rocky Mountain region. By
E. Lendell Cockrum and Kenneth L. Fitch. Pp. 281-292,
1 figure in text. November 15, 1952.

23. Comments on the taxonomy and geographic distribution of
North American microtines. By E. Raymond Hall and E.
Lendell Cockrum. Pp. 293-312. November 17, 1952.

24. The subspecific status of two Central American sloths. By
E. Raymond Hall and Keith R. Kelson. Pp. 313-337. November
21, 1952.

25. Comments on the taxonomy and geographic distribution of
some North American marsupials, insectivores, and
carnivores. By E. Raymond Hall and Keith R. Kelson. Pp.
319-341. December 5, 1952.

26. Comments on the taxonomy and geographic distribution of
some North American rodents. By E. Raymond Hall and Keith
R. Kelson. Pp. 343-371. December 15, 1952.

27. A synopsis of the North American microtine rodents. By E.
Raymond Hall and E. Lendell Cockrum. Pp. 373-498, 149
figures in text. January 15, 1953.

28. The pocket gophers (Genus Thomomys) of Coahuila, Mexico.
By Rollin H. Baker. Pp. 499-514, 1 figure in text.
June 1, 1953.

29. Geographic distribution of the pocket mouse, Perognathus
fasciatus. By J. Knox Jones, Jr. Pp. 515-526, 7 figures
in text. August 1, 1953.

30. A new subspecies of wood rat (Neotoma mexicana) from
Colorado. By Robert B. Finley, Jr. Pp. 527-534, 2 figures
in text. August 15, 1953.

31. Four new pocket gophers of the genus Cratogeomys from
Jalisco, Mexico. By Robert J. Russell. Pp. 535-542.
October 15, 1953.

32. Genera and subgenera of chipmunks. By John A. White.
Pp. 543-561, 12 figures in text. December 1, 1953.

33. Taxonomy of the chipmunks, Eutamias quadrivittatus and
Eutamias umbrinus. By John A. White. Pp. 563-582,
6 figures in text. December 1, 1953.

34. Geographic distribution and taxonomy of the chipmunks of
Wyoming. By John A. White. Pp. 584-610, 3 figures in
text. December 1, 1953.

35. The baculum of the chipmunks of western North America.
By John A. White. Pp. 611-631, 19 figures in text.
December 1, 1953.

36. Pleistocene Soricidae from San Josecito Cave, Nuevo Leon,
Mexico. By James S. Findley. Pp. 633-639. December 1, 1953.

37. Seventeen species of bats recorded from Barro Colorado
Island, Panama Canal Zone. By E. Raymond Hall and William
B. Jackson. Pp. 641-646. December 1, 1953.

Index. Pp. 647-676.

*Vol. 6. (Complete) Mammals of Utah, _taxonomy and distribution_. By
Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
August 10, 1952.

Vol. 7. *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303,
73 figures in text, 37 tables. August 25, 1952.

2. Ecology of the opossum on a natural area in northeastern
Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp.
305-338, 5 figures in text. August 24, 1953.

3. The silky pocket mice (Perognathus flavus) of Mexico. By
Rollin H. Baker. Pp. 339-347, 1 figure in text. February
15, 1954.

4. North American jumping mice (Genus Zapus). By Philip H.
Krutzsch. Pp. 349-472, 47 figures in text, 4 tables.
April 21, 1954.

5. Mammals from Southeastern Alaska. By Rollin H. Baker and
James S. Findley. Pp. 473-477. April 21, 1954.

6. Distribution of Some Nebraskan Mammals. By J. Knox Jones,
Jr. Pp. 479-487. April 21, 1954.

7. Subspeciation in the montane meadow mouse, Microtus
montanus, in Wyoming and Colorado. By Sydney Anderson.
Pp. 489-506, 2 figures in text. July 23, 1954.

8. A new subspecies of bat (Myotis velifer) from southeastern
California and Arizona. By Terry A. Vaughn. Pp. 507-512.
July 23, 1954.

9. Mammals of the San Gabriel mountains of California. By
Terry A. Vaughn. Pp. 513-582, 1 figure in text, 12 tables.
November 15, 1954.

10. A new bat (Genus Pipistrellus) from northeastern Mexico.
By Rollin H. Baker. Pp. 583-586. November 15, 1954.

11. A new subspecies of pocket mouse from Kansas. By E.
Raymond Hall. Pp. 587-590. November 15, 1954.

12. Geographic variation in the pocket gopher, Cratogeomys
castanops, in Coahuila, Mexico. By Robert J. Russell and
Rollin H. Baker. Pp. 591-608. March 15, 1955.

13. A new cottontail (Sylvilagus floridanus) from northeastern
Mexico. By Rollin H. Baker. Pp. 609-612. April 8, 1955.

14. Taxonomy and distribution of some American shrews.
By James S. Findley. Pp. 613-618. June 10, 1955.

15. The pigmy woodrat, Neotoma goldmani, its distribution and
systematic position. By Dennis G. Rainey and Rollin H.
Baker. Pp. 619-624, 2 figs. in text. June 10, 1955.

Index. Pp. 625-651.

Vol. 8. 1. Life history and ecology of the five-lined skink, Eumeces
fasciatus. By Henry S. Fitch. Pp. 1-156, 26 figs. in text.
September 1, 1954.

2. Myology and serology of the Avian Family Fringillidae, a
taxonomic study. By William B. Stallcup. Pp. 157-211, 23
figures in text, 4 tables. November 15, 1954.

3. An ecological study of the collared lizard (Crotaphytus
collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in
text. February 10, 1956.

4. A field study of the Kansas ant-eating frog, Gastrophryne
olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in
text. February 10, 1956.

5. Check-list of the birds of Kansas. By Harrison B. Tordoff.
Pp. 307-359, 1 figure in text. March 10, 1956.

6. A population study of the prairie vole (Microtus
ochrogaster) in northeastern Kansas. By Edwin P. Martin.
Pp. 361-416, 19 figures in text. April 2, 1956.

7. Temperature responses in free-living amphibians and reptiles
of northeastern Kansas. By Henry S. Fitch. Pp. 417-476, 10
figures in text, 6 tables. June 1, 1956.

8. Food of the crow, Corvus brachyrhynchos Brehm, in
south-central Kansas. By Dwight Platt. Pp. 477-498,
4 tables. June 8, 1956.

9. Ecological observations on the woodrat, Neotoma floridana.
By Henry S. Fitch and Dennis G. Rainey. Pp. 499-533,
3 figures in text. June 12, 1956.

10. Eastern woodrat, Neotoma floridana: Life history and
ecology. By Dennis G. Rainey. Pp. 535-646, 12 plates,
13 figures in text. August 15, 1956.

Index. Pp. 647-675.

Vol. 9. 1. Speciation of the wandering shrew. By James S. Findley.
Pp. 1-68, 18 figures in text. December 10, 1955.

2. Additional records and extensions of ranges of mammals from
Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M.
Hansen. Pp. 69-80. December 10, 1955.

3. A new long-eared myotis (Myotis evotis) from northeastern
Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84.
December 10, 1955.

4. Subspeciation in the meadow mouse, Microtus pennsylvanicus,
in Wyoming. By Sydney Anderson. Pp. 85-104, 2 figures in
text. May 10, 1956.

5. The condylarth genus Ellipsodon. By Robert W. Wilson.
Pp. 105-116, 6 figures in text. May 19, 1956.

6. Additional remains of the multituberculate genus
Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures
in text. May 19, 1956.

7. Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp.
125-335, 75 figures in text. June 15, 1956.

8. Comments on the taxonomic status of Apodemus peninsulae,
with description of a new subspecies from North China.
By J. Knox Jones, Jr. Pp. 337-346, 1 figure in text,
1 table. August 15, 1956.

9. Extensions of known ranges of Mexican bats. By Sydney
Anderson, Pp. 347-351. August 15, 1956.

10. A new bat (Genus Leptonycteris) from Coahuila. By Howard
J. Stains. Pp. 353-356. January 21, 1957.

11. A new species of pocket gopher (Genus Pappogeomys) from
Jalisco, Mexico. By Robert J. Russell. Pp. 357-361.
January 21, 1957.

More numbers will appear in volume 9.

Vol. 10. 1. Studies of birds killed in nocturnal migration. By
Harrison B. Tordoff and Robert M. Mengel. Pp. 1-44, 6
figures in text, 2 tables. September 12, 1956.

2. Comparative breeding behavior of Ammospiza caudacuta and
A. maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates,
1 figure. December 20, 1956.

3. The forest habitat of the University of Kansas Natural
History Reservation. By Henry S. Fitch and Ronald R.
McGregor. Pp. 77-127, 2 plates, 7 figures in text,
4 tables. December 31, 1956.

4. Aspects of reproduction and development in the prairie vole
(Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161,
8 figures in text, 6 tables. December 19, 1957.

More numbers will appear in volume 10.

Transcriber's Notes

With the exception of the list of typographical corrections below and minor corrections not noted here, the text presented here is the same as in the original printed version. Tables 1 and 2 were rotated so that the width would be less than the limit of 75 characters wide. In the tables, the title and some column headers were printed in small caps. Those are usually displayed as ALL CAPS; but for ease of reading, they were left as mixed case. The list of UKMNH publications was compiled at the end of the article's text.

Typographical Corrections

Page(s) Correction ============ ======================================= 129, 130, ii This publication: 4 tables => 6 tables 138 cyle => cycle

Text Emphasis

_Text_ - Italic

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