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

Natural History of the Prairie Vole
(Mammalian Genus Microtus)

By
E. W. JAMESON, JR.

CONTENTS

INTRODUCTION

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.

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."

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 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 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.

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

FOOD AND HABITAT

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]

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, 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.

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

ASSOCIATES

NEST AND BURROWS

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 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.

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.

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