NATURAL HISTORY OF THE

PRAIRIE VOLE

(Mammalian Genus Microtus)

BY



E. W. JAMESON, Jr.





University of Kansas Publications

Museum of Natural History


Volume 1, No. 7, pp. 125-151

October 6, 1947



UNIVERSITY OF KANSAS

LAWRENCE

1947

University of Kansas Publications, Museum of Natural History



Editors: E. Raymond Hall, Chairman; Donald S. Farner, H. H. Lane,

Edward H. Taylor



Volume 1, No. 7, pp. 125-151

October 6, 1947





University of Kansas

Lawrence, Kansas





PRINTED BY

FERD VOILAND, JR., STATE PRINTER

TOPEKA, KANSAS

1947



21-6957

[Pg 127]

Natural History of the Prairie Vole

(Mammalian Genus Microtus)

By

E. W. JAMESON, JR.

CONTENTS

[Pg 128]

INTRODUCTION

The prairie vole (Microtus ochrogaster) at Lawrence, Kansas, is
approximately 5-1/2 inches in length, of which the tail comprises 1-1/4
inches, and weighs approximately 1-1/2 ounces. The color on the
dorsum is dark gray with a grizzled appearance from the mixture of
black and fulvous on the long hairs; the venter is paler, sometimes
pale fulvous or cinnamon. The animal is compactly built much as
are the other microtine rodents. The short legs and short tail, small
eyes and partly hidden ears, and heavy and flattened head all suggest
its semifossorial mode of life. The prairie vole spends most
of its time in an elaborate system of tunnels (some entirely below
the ground) and in almost hidden galleries in the dense grass.

Microtus ochrogaster can be separated from other voles in its
geographic range by a combination of several characters. The plantar
tubercles usually number five, although a few individuals with six
tubercles were found at Lawrence, Kansas. Microtus pennsylvanicus,
normally with six plantar tubercles, as Bole and Moulthrop (1942:156)
pointed out, sometimes has only five. Therefore, the number
of plantar tubercles alone is not a certain means for separating
pennsylvanicus from ochrogaster. The color of the venter of ochrogaster
is usually fulvous or cinnamon instead of grayish as in pennsylvanicus,
but there is variation in this respect too; some prairie
voles also have a grayish venter. The shorter tail of ochrogaster
will assist in establishing its identity where it occurs with pennsylvanicus.
The third upper molar has two closed triangles in ochrogaster
and usually three in pennsylvanicus. The pelage of ochrogaster
is coarse whereas pennsylvanicus has fine fur. Prairie voles
may be separated from pine mice (Pitymys nemoralis and P. pinetorum)
with which they are sometimes found, by the larger eyes,
less rusty color, and longer tail. The Cooper lemming mouse (Synaptomys
cooperi) differs from the prairie vole in having the upper
incisors grooved, and in possessing a shorter tail which approximates
the hind foot in length.

Of Microtus ochrogaster from Lawrence, Douglas County, Kansas,
average measurements of twenty-five adult males are: total length,
143 (121-167) mm.; tail, 32 (25-42) mm.; hind feet, 20 (17-22)
mm.; weight, 43 (38-55) grams. Twenty-five adult females from
the same place average: total length, 150 (131-170) mm.; tail, 33
(31-41) mm.; hind foot, 19 (17-21) mm.; weight, 45 (38-58) grams.[Pg 129]

The prairie vole is found in suitable habitats in the central part of
North America. It has been recorded from Edmonton, Alberta, in
the northwest (Bailey, 1900:76), southeastward to Chesapeake, Ohio
(Bole and Moulthrop, op. cit.:156), and in the southwest as far as
Ft. Reno, Oklahoma (Bailey, op. cit.:74). See figure 1 showing the
known range of Microtus ochrogaster. Microtus ludovicianus, a close
relative of ochrogaster, has been taken along the southern part of
the boundary between Texas and Louisiana (Lowery, 1943:247).

The activities of voles, especially those of the genus Microtus, attracted
the attention of naturalists even in early times. Aristotle
(translated by Thompson, 1910) wrote: "The rate of propagation
of field mice in country places, and the destruction that they cause,
are all beyond telling. In many places their number is so incalculable
that but very little of the corn-crop is left to the farmer; and
so rapid is their mode of proceeding that sometimes a small farmer
will one day observe that it is time for reaping, and on the following
morning, when he takes his reapers afield, he finds his entire
crop devoured. Their disappearance is unaccountable: in a few
days not a mouse will be there to be seen."

Figure 1. Range of the Prairie Vole (Microtus ochrogaster).

Several early naturalists in this country commented on the fluctuations
in numbers of individuals, and on the breeding and feeding
habits of voles. Kennicott (1857) in an agricultural report on the
mammals of Illinois wrote about the breeding of the prairie vole.
He described its stores of plants and commented on the behavior
of some captives. Quick and Butler (1885) discussed the habits of[Pg 130]
Microtus ochrogaster as well as those of M. pennsylvanicus, Pitymys
pinetorum, and Synaptomys cooperi in Indiana, and described the
feeding and breeding habits of these species. Criddle (1926) gave an
account of the feeding and breeding habits of Microtus ochrogaster
in Manitoba, and Fisher (1945) published a short description of the
food and reproduction of the same species as he observed it in Missouri.
Stone investigated the fauna in the nests of this vole in the
same state, but has not yet, as of March, 1946, published his findings.

METHODS

The information in the present account was obtained by observing
animals in the field, and by examining trapped animals that were
brought into the laboratory. Five hundred individuals were caught
in snap-traps, and forty additional voles that were marked were captured
a total of 157 times. More than 90 per cent of the specimens
were trapped at Lawrence, Douglas County, Kansas, but voles were
examined also in Ellsworth, Atchison, and Jefferson counties, Kansas,
and in Douglas County, Illinois. My data pertain to Microtus
ochrogaster in the above named areas from October, 1945, until
August, 1946. The findings may not be typical of this species in
other areas and in other years.

The museum special traps were used both with and without bait.
The bait consisted of a piece of walnut meat on the treadle. By
placing the trap crosswise in the runway, voles were captured
whether or not the treadle was baited. Immediately upon removal
from the trap, each vole was placed in a white flannel sack, one sack
sufficing for several voles when necessary. In this way the loss of
ectoparasites was kept to a minimum. The fleas were counted, and
the numbers of lice and mites were estimated; some specimens of
ectoparasites were saved for identification.

The voles taken in live traps were marked and released. The
marking was done by cutting off one or more toes in such a manner
that the vole could later be identified. From left to right, the toes
were assigned numbers from one to five on the left hind foot, and by
tens from ten to fifty on the right hind foot. Number 33, therefore,
was assigned to the one vole of which the middle toe of each hind
foot had been cut off. Each time an animal was captured alive, it
was weighed, specimens of fleas, lice and mites were preserved, and
the external appearance of the reproductive organs was noted. The
extent of the molt line, if the vole was molting, was recorded. Corresponding
data were kept for each dead vole caught in a snap trap.[Pg 131]

Assistance is acknowledged from Professors E. Raymond Hall, A.
Byron Leonard, Worthie H. Horr, and Donald F. Hoffmeister; and I
have had also much helpful advice from Professors W. J. Hamilton,
Jr., and P. C. Stone.

MOLT

The skins of 44 molting prairie voles were pinned out flat. The
flesh sides clearly show the areas of molt. Various stages in the molt
process were observed also in animals caught in live traps. The
molt begins when the animal is three or four weeks old; at this time
the juvenal pelage is replaced by the subadult pelage. The second
molt occurs when the prairie vole is between eight and twelve weeks
old, and is the means by which the adult pelage replaces the subadult
pelage. These same two molts were found by Hatfield (1935)
to occur in captive Microtus californicus. Molting voles of the
species ochrogaster were trapped in each month of the year.

The molting processes of juveniles and subadults follow the same
pattern. The first area of molting is in the pectoral region. The
molt patch extends caudad toward the tail and cephalad toward the
chin. New pelage separates this area of active molt into two strips
on the fourth or fifth day. By this time each strip has spread laterad
to the legs and sides, and is 10 to 20 mm. wide. Ultimately each
strip unites with its opposite, usually at the center of the dorsum.
This area of molt then spreads cephalad and caudad. Fourteen to
fifteen days after the beginning of the molt, the entire dorsum is in
process of being covered with new pelage. Shortly before the completion
of the molt, the dorsal area of molt divides into two patches,
one on the rump and one on the nape. The areas last to be covered
with new pelage are the crown and that between the ears and the
eyes. A slight variation in the above process occurred in some
specimens in which the lateral strips joined immediately cephalad
of the tail instead of at the center of the dorsum. The entire process
takes approximately three weeks.

Large voles (45 grams or more) grow hair in irregular patches
that measured 5 to 15 mm. In these large voles the molt is accomplished
slowly and does not cover large areas of the body at any one
time. The small areas of molt are visible for 7 to 10 days, and were
found on approximately three quarters of the large voles examined.

[Pg 132]

FOOD AND HABITAT

The diet of the prairie vole reflects both its environment and its
choice of food. The plants eaten are usually green and succulent,
but some dry, hard seeds and small stems of woody plants are also
eaten. The vegetation, which supplies the food for the vole, is important
as cover or nesting material. For this reason food and
habitat are discussed together.

Types of Cover

Prairie voles inhabit areas where the dominant plants in summer
are clover or grasses or both. The lawn on the campus at the University
of Kansas consists mostly of several kinds of grasses, but in
some places alfalfa (Medicago sativa) replaces clover (Trifolium
sp.), and in other places sedges (Scirpus spp.) are found in addition
to the grasses. The grass is short; it is mowed to a length of 4 to 6
inches. Bluegrass (Poa pratensis) and crabgrass (Digitaria ischaemum)
form most of the sod. Bluejoint (Andropogon furcatus) is
common in a sparsely wooded part of the campus, an area which has
many voles. Foxtail (Setaria lutescens and S. viridis) and prairie
threeawn (Aristida oligantha) are also common on the lawn, but
these become dry in late summer, and at that time supply neither
food nor cover for the voles. The voles make well-beaten depressions
in the sod, and the grass arches over them to form canopies.

In the winter, when the snow flattened the grass on the campus
so that there were no longer protective canopies of blades over the
runways of the voles, they migrated into areas of Japanese honeysuckle
(Lonicera japonica). At this season the honeysuckle was
their main food. In areas where this vine was not available, the
voles abandoned their surface runways and remained below the
ground, coming to the surface only under the protection of a blanket
of snow. The voles returned to the grass and clover habitat in
March and April in 1946.

One pure stand of Ladino clover in Jefferson County, Kansas, was
studied in late November and early December of 1945. The clover
was 2 to 4 inches high, and although it was the sole food of the
voles, it furnishes but little cover. They were common here; 300
traps yielded 111 voles in two nights.

[Pg 133]

Cuttings

The voles seek particularly the tender heads of grasses and the
terminal leaves of sweet clover (Melilotus alba). To obtain these
parts, the voles begin by cutting through the base of the plant. The
surrounding plants are often near enough to support the freshly cut
piece in an upright position. The vole makes successive cuttings,
40 or 50 millimeters from the ground, until the desired parts of the
plant are within reach. The cuttings that have accumulated at the
base of the plant may be eaten, but frequently they remain as evidence
of the vole's feeding activity.

On May 12, 1946, an analysis was made of the cuttings found in
an area of alfalfa, grasses, and weeds. From table 1 it may be seen
that quackgrass, alfalfa, wild lettuce, and cleavers were common.
In three nights 70 traps caught 8 prairie voles and 3 deer mice; no
pine mice or cotton rats were caught on the area. The stomachs of
the voles and the deer mice were examined, and only the stomachs
of the voles contained green material. Analysis of the cuttings (see
table 2) indicates that alfalfa was eaten in greater quantity than
any other plant; it made up almost three quarters of the cuttings although
but one quarter of the cover. All other plants occurred less
commonly in the piles of cuttings than they did in the estimated
composition of the cover. Grasses and wild lettuce were next to
alfalfa in importance.

Table 1.—The Relative Abundance of Plants in an Area of Alfalfa, Grasses,
and Weeds[A]

Table 2.—Composition of Ten Piles of Cuttings[B]

[Pg 134]

Approximately one out of every ten voles caught in snap traps had
a piece of plant in its mouth. Occasionally a vole took a piece of
food into a live trap. Evidently the food is not always eaten where
it is procured. Grasses of the genus Poa are the kinds most frequently
found in the mouths of dead voles. Bromus carinatus, B.
inermis and sweet clover (Melilotus alba) were found in the runways.
The pulpy fruit of the horse nettle (Solanum carolinense) was found
partly eaten, especially near the entrances to underground passages.

Food Caches

Caches of seeds and underground parts of plants are stored in subterranean
chambers. One lot of food was found stored on the surface
of the ground. Four times, piles of seeds in runways indicated the
species of plants which the voles were storing.

One underground cache was found on May 27, 1946, on the University
campus, by John Evans, Richard Edgar, and the writer.
This cache was in a large chamber in a tunnel system of the prairie
vole, on an east-facing hillside of walnut trees, catalpas, and Kentucky
coffee trees. The oval chamber was 250 mm. wide, 400 mm.
long, and 200 mm. high. The roof, at its highest point, was 30 mm.
below the surface of the ground. There were two entrances to the
cavity, both on the downhill side. The cache consisted of eight
quarts of seeds (approximately 2,800) of the Kentucky coffee tree
(Gymnocladus dioica). The seeds were packed with earth and all
were well preserved. The site of this cache was in an area which
was shaded by a small coffee tree. A seed of this tree is spheroidal,
measures 17 mm. in width, and weighs 2 grams.

Several times in the fall of 1945, in the above-mentioned grove,
the writer found pods of the coffee tree lying in the runs of the
voles. These pods were sometimes entire, but more often they had
been gnawed; frequently only part of a pod remained, indicating
that the voles were storing or feeding upon the seeds, although the
possibility that the mice were storing food did not occur to the writer
at the time. Three times, seeds of other plants were found piled at
the entrances of the burrows of voles. Twice these piles consisted
of from 50 to 70 seeds of the common dandelion (Taraxacum
officinale). The third pile was composed of 20 seeds of the giant
ragweed (Ambrosia trifida).

A pasture of Canadian bluegrass (Poa compressa), wild millet
(Echinochloa crusgalli), sedges (Scirpus spp.), and clover (Trifolium
sp.) in Atchison County, Kansas, was examined in November,[Pg 135]
1945. This area was the home of a dense population of prairie
voles. Wherever a path of the voles crossed a deep imprint of a
horse's hoof, there was a collection of cuttings from the horizontal
stems of the clover which bordered the runways. Some of the cuttings
may have been made by lemming mice (Synaptomys cooperi)
which were also common in the area.

Several kinds of voles store food. Bailey (1920) wrote of the
caches of Microtus pennsylvanicus in North Dakota, where, in one
locality, this vole was known as the bean mouse. He stated that the
Indians dug up beans (Falcata comosa) and the tubers of the
Jerusalem artichoke (Helianthus tuberosus) which the voles had
stored. Lantz (1907:17) found a cache of the roots of wild morning
glory (Convolvulus sepium) laid away by Microtus pennsylvanicus.
Nelson (1893:140) wrote that, as winter approached,
Microtus operarius gathered small bulbous roots, sometimes storing
a peck or more in a single cavity. Fisher (1945) in Missouri found
a gallon of the fruits of the horse nettle (Solanum carolinense)
stored in a hollow stump by the prairie vole. Kennicott (1857:99)
found five or six quarts of roots of two species of spike-flower
(Liatrus), Helianthus, and various grasses among the winter provisions
of the prairie vole in Illinois.

Plants Used as Food and as Cover

Table 3 lists, according to their families, the species of plants
which the prairie vole was observed to use for food. The same
species are sometimes used as cover. The majority of the plants are
in three families: the grass family (Graminae), the pulse family
(Leguminosae), and the composite family (Compositae).

The grasses that supply the voles' food and cover are mostly Poa
(the bluegrasses) and Bromus (bromegrass, chess, or cheat). Poa
pratensis is a common lawn and pasture grass, P. annua is a weed
species. The bluegrasses begin to grow in late winter about Lawrence,
Kansas, and they remain green until late in the fall. During
this time, the voles eat the blades and heads of bluegrass, and make
their runways under the culms. The prairie voles utilize several
species of Bromus. Bromus inermis and B. carinatus are important
range and pasture grasses, but japonicus is a weed of little or no
economic value. These are soft, tender grasses, but, in contrast to
the bluegrasses, they become dry in midsummer, and are then unsuitable
as food. However, they continue to form a protection over
the runways of the voles.[Pg 136]

The legumes, which appeared to be most important to the prairie
vole, are clover (Trifolium spp. and Melilotus alba) and alfalfa
(Medicago sativa). These plants are common in both cultivated and
feral states. They form a different type of cover from that made
by grasses. Voles, living in clover and alfalfa, do not make runways
as distinct as they do in grasslands. The clover and alfalfa
plants are branched and of a spreading growth form, whereas the
grasses have leaves which are appressed to the main stem. The individual
grass plants grow close together, and a vole cannot run
through grass without trampling some of it. As voles use the same
paths repeatedly, the grass in their runs becomes flattened and dies.
There is sufficient room between the stems of the clover and alfalfa
plants to allow the voles to pass through without treading on the
stems. In such a habitat, vole runways are poorly developed, and
are difficult to find. Voles in grasslands feed in runways, as attested
by the piles of cuttings found in the runways and the nibbled
grass which borders them. Voles in clover or alfalfa feed at the
bases of the plants wherever the plants may grow. In the latter
type of cover the cuttings are rather evenly distributed.

Compositae formed a minor part of the cover in most of the habitats
studied. Many grasslands have a stand of dandelions; sow
thistle, wild lettuce, and ragweed were also common in some grasslands.
The voles ate the leaves and sometimes the seeds and underground
parts of these plants.

Table 3. Plants Used for Food by the Prairie Vole

[Pg 137]

ASSOCIATES

In the mixed areas of grassland and clover that were described
above, the cotton rat (Sigmodon hispidus), the deer mouse (Peromyscus
maniculatus), and the little short-tailed shrew (Cryptotis
parva) were commonly caught in the runways of the prairie vole.
Less frequently trapped were the common mole (Scalopus aquaticus),
the large short-tailed shrew (Blarina brevicauda), the Cooper
lemming mouse (Synaptomys cooperi), the pine mouse (Pitymys
nemoralis), and the harvest mouse (Reithrodontomys megalotis).
In the dense growth of Japanese honeysuckle, the prairie vole shared
runways with the white-footed mouse (Peromyscus leucopus), the
large short-tailed shrew, and the pine mouse.

NEST AND BURROWS

The prairie vole makes a tortuous network of paths through the
grass and honeycombs the topsoil with its tunnels. The underground
passages lead to nests or to chambers where food is sometimes stored.
The runways through the grass are 40 to 50 mm. wide, and usually
lie slightly below the surface of the ground. By using the same
path repeatedly, the voles create little ruts in which they run. The
bottom of the runways are bare soil or are covered with only a thin
layer of trampled grass. Cotton rats, on the other hand, apparently
do not use their runs over long periods, for they are not well-beaten
runways, but are made merely by parting the grass and not by
trampling it down or cutting it off. Voles were trapped in runways
of the cotton rats, but no cotton rat was caught in a typical runway
of a vole.

The burrows of the prairie vole are 40 to 50 mm. in diameter, and
the shallowest part is usually 50 to 100 mm. below the surface of the
ground. Burrows leading to nests or food chambers may descend
deeper than the others. Some prairie voles were trapped in tunnels
of the common mole (Scalopus aquaticus). The voles make their
own burrows, and are especially active at this task when a hard rain
has loosened the previously hard, dry soil. The rain in the first two
weeks of October, 1945, made the soil much more friable than it had
been at the beginning of the month, and the voles took advantage of
the favorable opportunity to construct many new burrows. In October,
particles of soil were packed beneath the toenails of many
specimens.

In this time fifteen nests were found. They were 6 to 18 inches
below the surface of the ground, and two tunnels led from each nest[Pg 138]
to the surface runway. The nest cavities were spheroidal, and
measured 150 to 200 mm. horizontally, and 80 to 100 mm. vertically.
The floors were slightly concave and were covered with loose dirt
and a mixture of dried grass and one or two leaves. The remainder
of the cavity was filled with the dry grass of which the nest was
composed. Criddle (1926) stated that at Treesbank, Manitoba, this
vole makes its nests in the burrow systems of the pocket gopher
(Thomomys talpoides); and Kennicott (1857:98) found nests of
the prairie vole in old ant hills.

Each of two nests that had been recently occupied was placed in a
Berlese funnel, and in this way the arthropod fauna of the nests
was collected. The most common arthropods in the nests were mites
(parasitic, predaceous, and free-living) and springtails. Sowbugs,
centipedes, spiders, and fleas were also present. Of these arthropods,
the laelaptid mites, one kind of tick, and one kind of flea have a
direct relationship with the vole. These parasites are the same
species which are found on the vole itself. The mites were Eulaelaps
stabularis (Koch) and Atricholaelaps glasgowi (Ewing). One adult
tick, Ixodes sculptus Newman, was in one nest. The fleas, about a
dozen in each nest, were Ctenophthalmus pseudagyrtes Baker, the
flea most frequently found on the prairie vole.

EXTERNAL PARASITES

The pelage of prairie voles, pine mice, deer mice, and shrews forms
a habitat for many kinds of parasitic arthropods. The fleas, lice,
and mites from the prairie vole were collected, counted, and identified.
The ectoparasites from the other small mammals living in the
same habitat as the prairie vole were also considered. Some ectoparasites
begin to leave the host when it dies, and any counts of
ectoparasites made from snap-trapped voles may fall short of the
number which was on the animal when it was alive. The average
number of fleas recorded from live voles exceeds that found on snap-trapped
voles (see table 4). The numbers of lice and mites were
estimated, but selected voles were examined to obtain absolute numbers
of these kinds of ectoparasites.

The fleas, lice, and mites were mounted on one inch by three inch
glass slides; the ticks were preserved in 70 per cent alcohol. Dr. E.
W. Baker identified the mites; Dr. R. A. Cooley and Dr. Glen M.
Kohls, the ticks; Dr. G. W. Wharton, the chiggers; and Dr. Gordon
F. Ferris, the lice. To each of these gentlemen I am grateful. The
fleas were identified by myself.

[Pg 139]

Fleas (Siphonaptera)

The information on the average numbers of fleas on voles was obtained
from live-trapped and some snap-trapped voles. Fleas were
counted only on voles which were removed from the traps within
twenty-four hours after the traps had been last examined. The
average numbers of fleas found on prairie voles in this study are
given in table 4.

Table 4. Average Numbers of Fleas on Prairie Voles[C]

Table 5 shows the average degree of infestation for ten months of
an eleven month period. The monthly averages for the most part
show no variations. The latter half of February provides an exception
in that a series of 22 snap-trapped voles and 11 live-trapped
voles taken at that time had on the average, 9.7 and 5.3 fleas respectively.
Pine mice (Pitymys nemoralis) occurred in small numbers
in the area where Microtus ochrogaster was live-trapped, and
Ctenophthalmus pseudagyrtes was the flea found to be common on
both of these voles.

Table 5.—Monthly Averages of Fleas on Prairie Voles

Some fleas have a habitat preference as well as a host specificity.
As voles from different areas were examined, different kinds of fleas
were encountered. A population of free-living voles under observation
on the Campus at Lawrence was parasitized only by Ctenophthalmus
pseudagyrtes. From 90 prairie voles collected in a field
of clover 4 miles northwest of Lawrence, the only species of flea
recovered was Orchopeas leucopus. In both places the prairie vole
was the most common mammal, but in the field of clover three deer
mice (P. maniculatus) also were trapped. In a third field, one mile
west of Lawrence, the prairie vole was host to both the above mentioned
fleas. Here both the prairie vole and the cotton rat (Sigmodon
hispidus) were common.[Pg 140]

The host distribution of fleas on seven small mammals which lived
in the same habitats as the prairie vole is given in table 6.

Table 6.—Frequency of Occurrence of Fleas on Seven Species of Small Mammals[E]

Column headings:



A: Cryptotis parva

B: Blarina brevicauda

C: Peromyscus maniculatus

D: Peromyscus leucopus

E: Sigmodon hispidus

F: Microtus ochrogaster

G: Pitymys nemoralis

It is seen that some fleas are rather specific in their choice of hosts,
and that others are commonly found on two or more small mammals
in the same habitat. In each of these groups there are fleas which
have a habitat preference, that is to say, the flea lives on the host
when the host lives in a given habitat, but is absent when the host
lives in another habitat.

Group 1: Fleas with a Host Preference

Epitedia wenmanni was found on the white-footed mouse (Peromyscus
leucopus) and only rarely on the prairie vole. Corrodopsylla
hamiltoni was taken only from the two kinds of shrews
(Blarina brevicauda and Cryptotis parva). Fleas on shrews may
have a well-developed host preference. At any rate, Elton, Baker,
Ford, and Gardner (1931) found that Doratopsylla dasycnemus
rarely strayed from its normal host (Sorex araneus) to other small
mammals. Peromyscopsylla scotti was taken from the white-footed
mouse (Peromyscus leucopus), and had a habitat preference also.
It was found only on those white-footed mice which were trapped in
the woodlands at various places in Douglas County; white-footed
mice which were trapped in areas of brush were free of this parasite.

[Pg 141]

Group 2: Fleas Commonly Found on Two or More Kinds of
Small Mammals

Orchopeas leucopus was an outstanding example of this group. It
was the most common flea on the deer mouse, the white-footed
mouse, and the cotton rat. In certain areas it was common on the
two voles (Pitymys nemoralis and Microtus ochrogaster). Ctenophthalmus
pseudagyrtes is the most abundant flea on the two kinds
of voles and on the large shrew (Blarina brevicauda), and was found
sparingly on the cotton rat.

Several kinds of fleas do not belong in either of the above groups.
Some fleas were accidental strays from mammals not included in
table 6; and one flea (Rectofrontia fraterna) may prove to be a common
nest parasite. Orchopeas howardii is common on tree squirrels
(Sciurus niger and S. carolinensis). Nosopsyllus fasciatus is a cosmopolitan
flea on Rattus norvegicus. Rectofrontia fraterna was
taken once from a prairie vole. Since the only specimens in the University
of Kansas Entomological Collections are from "mouse nests,"
this flea may be found to be a nest inhabiting parasite.

Some fleas are possible bridges by which a blood parasite could be
transmitted from one kind of a mammal to another. If Ctenophthalmus
pseudagyrtes acted as the intermediate host of a disease-causing
organism, an epizootic from Microtus ochrogaster might be
transmitted to Pitymys nemoralis or to Sigmodon hispidus or Blarina
brevicauda. There are several other such potential bridges for blood
parasites. Although table 6 does not prove that individual fleas
wander from one host to another, the frequency with which the several
kinds of fleas are removed from live mice suggests that the fleas
occasionally do so.

Lice (Anoplura)

Lice collected from the prairie vole were all of one species, Hoplopleura
acanthopus (Burmeister). Of 59 voles examined for the
presence of lice, 33 were found to be parasitized; the 59 voles had
an average of 3.4 lice each. Other mice which used the same runways
as the prairie vole had their own species of Anoplura. The
cotton rat was host to Hoplopleura hirsuta Ferris, and the two
species of Peromyscus were parasitized by Hoplopleura hesperomydis
(Osborn).

The writer collected Hoplopleura acanthopus from Microtus californicus
at Calaveras Dam, Alameda County, California, and from
M. pennsylvanicus at Ithaca, Tompkins County, New York. Elton,[Pg 142]
Ford, Baker, and Gardner (1931) recorded this same species from
M. argestis in England.

Lice on the prairie vole are the same species as those found on
other species of Microtus in other areas, but since Anoplura of the
prairie vole do not parasitize the cotton rat, the white-footed mouse,
and the deer mouse, this host specificity of lice makes it unlikely
that lice would carry blood parasites from the prairie vole to any
of the latter named rodents.

Mites (Acarina except Ixodoidea)

Many of the small mammals examined in this study had mites,
some of which were collected and identified. Mites were collected
from other species of voles in several localities in the United States
and in one locality in Canada; as voles in widely separated regions
are sometimes hosts to the same species of mites, these records will
be presented here.

The frequency of some kinds of mites in the identified material
suggests that they are more abundant than other kinds. The occurrence
of mites on small mammals from Lawrence, Kansas, is presented
in table 7.

The following comments can be made concerning the specificity
and geographic ranges of several species of mites:

Liponyssus occidentalis Ewing was found only on Cryptotis parva.

Eulaelaps stabularis (Koch) was one of the more common kinds
found on the prairie vole. This mite is rather large (about 1 mm.
long) and is frequently (with the following species) seen running
through the pelage of its host. In addition to the records for this
species in table 1, it was found to be a common parasite on Pitymys
pinetorum at Point Abino, Welland County, Ontario. Elton, Ford,
Baker and Gardner (1931) found this same mite on Apodemus
sylvaticus and Clethrionomys glareolus in England.

Atricholaelaps glasgowi, like the preceding species, was one of the
commoner mites on the prairie vole. It was found also on Pitymys
pinetorum at Point Abino, Welland County, Ontario; on Microtus
pennsylvanicus at Ithaca, Tompkins County, New York; and on
M. californicus at Calaveras Dam, Alameda County, California.

Atricholaelaps sigmodoni occurred only on the cotton rat.

Laelaps kochi was less commonly found than Eulaelaps stabularis
and Atricholaelaps glasgowi. In Kansas the prairie vole and
the cotton rat were hosts to Laelaps kochi, and it occurred on[Pg 143]
Microtus pennsylvanicus at Ithaca, New York, and on M. californicus
at Berkeley, California.

Trombiculidae are commonly known by their larvae which are
called chiggers or harvest mites. The white-footed mouse, the cotton
rat, and the prairie vole were parasitized at Lawrence. In the
winter these mites live in the ears of these small mammals, but in the
summer they were found both in the ears and on the rump. Those
obtained in winter were Ascoschöngastia brevipes (Ewing); other
species may be involved.

Listrophoridae was represented on the prairie vole by a species of
Myocoptes and a species of Listrophorus. These mites cling to the
hairs of their host, and do not occur on the skin of the voles.

No evidence was seen that mites had any ill effect on the health of
their hosts. No voles had scabs on the skin; and the ears were not
swollen and disfigured as they sometimes are by chiggers. Although
the identity of a specimen of mite could not be determined
until it was mounted, a person could tell whether or not it was one
of the larger, very active Laelaptidae, one of the hair-clinging
Listrophoridae, or one of the tiny, orange Trombiculidae.

On July 12, 1946, three prairie voles were examined to determine
the number of mites they supported. The voles were freshly caught,
no one of them having been dead for more than five minutes before
they were examined. These three voles had an average of 25
Laelaptidae, 22 Listrophoridae, and 53 Trombiculidae.

Six species of mites (Ixodoidea excepted) were found on the
prairie vole. Four of these were collected also from other small
mammals living in the same habitat as this vole. Two species of
mites were found to occur on voles in New York, Kansas, and California.

Ticks (Ixodoidea)

Two kinds of ticks were found. One adult specimen of Ixodes
sculptus Neumann was clinging to the head of a vole, just in front
of its eye. This species of tick was taken also from the thirteen-lined
ground squirrel (Citellus tridecimlineatus) at Lawrence. One
nymph of Dermacentor variabilis (Say) was found attached to the
scapular region of a prairie vole. Both of these specimens were
taken in June.

[Pg 144]

Table 7. Host Distribution of Mites on Seven Small Mammals[F]

Column headings:



A: Scalopus aquaticus

B: Cryptotis parva

C: Blarina brevicauda

D: Peromyscus maniculatus

E: Peromyscus leucopus

F: Sigmodon hispidus

G: Microtus ochrogaster

REPRODUCTION

Age Classes

Each prairie vole was assigned to one of three age classes (juvenile,
subadult, or adult) principally on the basis of weight, but partly on
the quality and color of the pelage. The three age classes are characterized
in table 8.

Table 8. Characters of Juvenile, Subadult, and Adult Prairie Voles

Fecundity

Hamilton (1941:4) found for Microtus pennsylvanicus that macroscopic
tubules of the cauda epididymis were an indication of
fecundity. By noting the size of the tubules (whether macroscopic
or not) and by making smears from them in approximately every
25th male caught, I found that the presence of sperm was positively
correlated with large-sized tubules of the cauda epididymis in Microtus
ochrogaster. Inferentially, males with sperm were fecund.

There is a relationship almost positive between the size of the
tubules of the cauda epididymis and the length of the testes. Testes[Pg 145]
longer than 7 mm. have macroscopic tubules in the cauda, and in
testes shorter than 7 mm. these tubules cannot be seen with the
naked eye, Hamilton (1937b) found that in M. pennsylvanicus[Pg 146]
testes smaller than 8 × 4 mm. did not contain sperm. The testes of
the prairie vole descend into the scrotum in the breeding season. In
the two winter months, when the voles did not bring forth young, the
testes decreased in size (see figure 3) and were withdrawn into the
body cavity. The presence of the testes in the body cavity does
not mean that a vole is not in breeding condition, for many specimens
with abdominal testes were fecund.

The females were considered to be fecund if they were gravid, or
if there were placental scars in the horns of the uteri.

Figure 2. Fecundity of Prairie Voles by Months. Adults and Subadults are
Considered Together.

Figure 3. Seasonal Changes in the Length of Testes.

Size of Litters

The number of mammae characteristic of a species of vole may
be a rough guide to the average size of a litter for that species.
The prairie vole has fewer mammae (three pairs) than some other
voles in North America, and might, therefore, be expected to have
smaller litters. Fifty-eight gravid females of Microtus ochrogaster
examined by me had an average of 3.4 embryos each; the number
of embryos ranged from one to seven. Hamilton (1936a) gave 5.07
as the average number of young per litter in M. pennsylvanicus.
Hatfield (1935) stated that M. californicus has an average of 5.7
young in a litter. Both pennsylvanicus and californicus normally
have four pairs of mammae. The expectation as to the size of the
litter seems to be realized. In the prairie vole one pair of mammae
is pectoral and two pairs are abdominal. Usually a lactating vole
showed evidence of only the abdominal mammae having been in use.

The size of litters was found to vary with the season of the year
(see table 9). Gravid females were collected in every breeding
month except September.

Table 9. Average Size of Litters of Microtus ochrogaster by Months[G]

Table 9 shows that the prairie vole produced the largest litters in
March. A comparison of table 9 with figure 2 shows that the largest
litters were produced at the height of the breeding season. Baker
and Ransom (1933), studying Microtus agrestis, also found that
larger litters were characteristic of the height of the breeding season;
and that at the beginning and at the end of the breeding season the
litters averaged smaller.[Pg 147]

The size of litters varied also with the age of the female. To place
a gravid female in its proper age class, the weight of the embryos
was subtracted from the total weight, and the remaining weight was
used as the body weight. The average size of the litters of 14 subadults
was 2.9, and in 35 adults it was 3.4. Hatfield (op. cit.)
found that the younger females of M. californicus gave birth to
smaller litters than did the adults.

Not included in either of the above analyses are nine gravid
females collected in November in a pasture watered by an artesian
spring in Atchison County, Kansas. In this pasture there was a
high concentration of prairie voles, and the percentage of fecundity
was much higher than in Douglas County at the same time. In
November only 29 per cent of the female prairie voles in Douglas
County were fecund, as against 59 per cent in Atchison County. The
average number of embryos of these nine voles was 4.1. Data from
Atchison County are not included in table 9.

The Breeding Season

In October, 1945, when this study was begun, the prairie vole was
bringing forth young. In the winter of 1945-'46 at Lawrence, Kansas,
there was a cessation of reproduction. The reproductive activity
was measured in terms of the fecundity of the subadults and the
adults of both sexes. Figure 2 suggests that the decline was most
marked in December and January; no gravid females were collected
in these two months, although two females trapped in the first week
of December were lactating. In October, November, and December,
85 per cent of the breeding females were adults. In October, 85 per
cent of the adult females were fecund, and in November, this figure
was 80 per cent. Reproduction at this season, in the females, it
appears, was largely a function of the adults. The proportion of
adults to the rest of the population was calculated for each month;
and the monthly changes in relative numbers of adults is shown in
figure 4. In November, December, and January there was a scarcity
of adult voles in the population. The autumnal decline in reproduction
occurred simultaneously with the disappearance of these
adults, and is thought to have been largely a result of it.

Reproductive activity began in February; and in this month one-third
of the females contained embryos, and 90 per cent of the males
were fecund. Reproduction reached its height in March when fecundity
for the females and males was 77 per cent and 100 per cent
respectively. In April both sexes showed signs of being less productive,[Pg 148]
and still later in the spring the percentage of fecundity remained
at slightly over 65 for both sexes, this figure being higher
for the males than for the females for any one month. From January
to February there was a 30 per cent increase in the percentage
of adults in the population; and for this period, there was a 33 per
cent increase in the fecundity of both males and females. In February,
80 per cent of the fecund females were adults. The breeding
in the late winter, as in the fall, is thought to depend upon the percentage
of adults in the population. Hamilton (1937b) noted a
similar correlation between winter breeding and dominance of adults
in Microtus pennsylvanicus in New York. Fisher (1945) found that
the prairie vole continued to breed throughout the winter of 1943-'44
in Missouri; in such a case, one would expect to find a large proportion
of adults in the population.

Figure 4. Seasonal Changes in the Numbers of Adults in Relation to the Total Population
of Prairie Voles.

Throughout the winter of 1945-'46, at Lawrence, the majority of
males were fecund; but fecundity in the females was much less, and
in January, no females showed signs of reproductive activity. From
this it appears that the females, not the males, limit the breeding
season of this species.

[Pg 149]

SUMMARY

In the eleven month period, October, 1945, until August, 1946, in
northeastern Kansas, more than five hundred specimens of the
prairie vole (Microtus ochrogaster) were examined in the flesh; and
forty free-living voles were examined 157 times—an average of
slightly less than four times each.

There is a complete molt from juvenal to subadult pelage, and
one from subadult to adult pelage. These molts require three weeks
each. Subsequent molts are irregular and extend over longer periods
of time.

This vole, in summer, inhabits areas of grass, clover, and alfalfa.
In winter, habitats with some woody growth may be sought.
Twenty-two kinds of plants were found to be used for food. Although
most of these were succulent plants, seeds and small woody
stems were sometimes eaten. The prairie vole, like some other
species of Microtus, lays away stores of food, usually underground;
the maximum quantity found in one cache was two gallons.

Nine other species of small mammals occur in the same habitat
with the prairie vole, and frequently use its runways. The vole
makes a network of paths through the grass, and constructs its own
burrows which lead to its nests and food stores. Each of fifteen
nests found were underground. Most, if not all, of the underground
tunnels are dug when the soil is moist, not when the soil is dry.

The commonest flea on the prairie vole is Ctenophthalmus pseudagyrtes;
it averages 1.9 (for subadult voles) to 3.4 (for adult voles)
per individual vole. Other fleas on this vole are Orchopeas leucopus,
Orchopeas howardii, Nosopsyllus fasciatus, Epitedia wenmanni, and
Rectofrontia fraterna. The two species of fleas which were actually
common on the vole (C. pseudagyrtes and O. leucopus), parasitized
also some other small mammals which lived in the same habitat as
the vole. One species of sucking louse (Hoplopleura acanthopus)
and two kinds of mites (Laelaps kochi and Atricholaelaps glasgowi)
which occur on the prairie vole in Kansas, occur also on
Microtus californicus in California and on M. pennsylvanicus in
New York. Only three ticks (1 Dermacenter variabilis and 2
Ixodes sculptus) were found on the prairie vole.

Fifty-eight gravid females had an average of 3.4 embryos. Litters
at the height of the breeding season are larger than those at the beginning
and at the end of the breeding season. Reproduction in
Microtus ochrogaster ceased in December, 1945, in northeastern
Kansas, and the first evidence of reproduction in 1946 was observed
in February.

[Pg 150]

LITERATURE CITED

Bailey, V.

1900. Revision of the American voles of the genus Microtus. N. Amer.
Fauna, 17:1-88, June 6, 1900.

1920. Identity of the bean mouse of Lewis and Clark. Jour. Mamm.,
1:70-72, November 28, 1919.

Baker, J. R., and Ransom, R. M.

1933. Factors affecting the breeding of the field mouse (Microtus agrestris).
Part 11. Temperature and food. Royal Soc. London Proc., (Ser. B)
112:39-46, November 1, 1932.

Bole, B. P., Jr., and Moulthrop, P. N.

1942. The Ohio Recent mammal collection in the Cleveland Museum of
Natural History. Sci. Pub. Cleveland Mus. Nat. Hist., 6:83-181, September
11, 1942.

Criddle, S.

1926. Habits of Microtus minor in Manitoba. Jour. Mamm., 7:193-200,
August 9, 1926.

Elton, C. S., E. B. Ford, J. R. Baker, and A. D. Gardner.

1931. The health and parasites of a wild mouse population. Proc. Zoöl.
Soc. London, 101:657-721, September 30, 1931.

Fisher, H. J.

1945. Notes on voles in central Missouri. Jour. Mamm., 26:435-437, November,
1945.

Hatfield, D. M.

1935. A natural history study of Microtus californicus. Jour. Mamm.,
16:261-271, November 15, 1935.

Hamilton, W. J., Jr.

1937a. The biology of microtine cycles. Jour. Agr. Res., 54:779-790, May
15, 1937.

1937b. Growth and life span of the field mouse. American Nat., 71:500,
September-October, 1937.

1941. The reproduction of the field mouse, Microtus pennsylvanicus (Ord).
Cornell Univ. Agr. Exp. Sta. Memoir 237, pp. 1-23, May, 1941.

Kennicott, R.

1856. The quadrupeds of Illinois. Part I, Rep. Commiss. Patents: Agriculture,
pp. 52-110, 1857.

Lantz, D. E.

1907. An economic study of field mice (genus Microtus). U.S.D.A. Bull.
Biol. Surv., 31:1-64, October 28, 1907.

Lowery, G. H., Jr.

1943. Check-list of the mammals of Louisiana and adjacent waters. Occas.
Papers Mus. Zoöl., Louisiana State Univ., 13:213-257, November 22,
1943.

[Pg 151]

Nelson, E. W.

1893. Description of a new species of Arvicola, of the Mynomes group, from
Alaska. Proc. Biol. Soc. Washington, 8:140-142, December 28, 1893.

Quick, E. W., and A. W. Butler.

1885. The habits of some Arvicolinae. American Nat., 19:113-118, February,
1885.

Transmitted August 13, 1946.

21-6957

Transcriber's Notes

Page 136, Table 3, under Compositae: changed Loctuca to Lactuca

(_Loctuca scariola_)



and changed artemsiifolia to artemisiifolia

(_A. artemsiifolia_)



Page 139: changed trappd to trapped

(from live-trapped and some snap-trappd voles.)



and changed rate to rat

(the prairie vole and the cotton rate)



Page 141: changed Almeda to Alameda

(at Calaveras Dam, Almeda County, California,)



Page 142: kept section heading: Mites (Acarina except Ixodoidea)

(the TOC lists the variation Acari instead of Acarina)



and changed Almeda to Alameda

(at Calaveras Dam, Almeda County, California.)



Page 143: changed tridecimlineaus to tridecimlineatus

(ground squirrel (_Citellus tridecimlineaus_) at Lawrence.)

Note: Another spelling variation is: tridecemlineatus.



Page 146: changed table 2 to table 9

(A comparison of table 2 with figure 2 shows that the largest)



Page 143: kept spelling variation: Dermacentor variabilis



Page 149: kept spelling variation: Dermacenter variabilis



Page 150: changed LITERAURE to LITERATURE

(LITERAURE CITED)



and kept spelling variation: agrestris, being a reference citation

(1933. Factors affecting ... field mouse (_Microtus agrestris_)).