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.

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]

SpeciesPercentage by number of plants

Quackgrass (Agropyron repens)30

Speargrass (Poa annua)01

California brome (Bromus carinatus)01

Smooth brome (Bromus inermis)01

Alfalfa (Medicago sativa)25

Peppergrass (Lepidium densiflorum)02

Cleavers (Galium aparine)15

Wild lettuce (Lactuca scariola)25

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

SpeciesTen piles of cuttingsFrequency of occurrence

Agropyron repens1002006190413

Poa annua000000000000

Bromus carinatus0000010000004

Bromus inermis000000000000

Medicago sativa401430303150021473

Lepidium densiflorum000000000000

Galium aparine000010100001

Lactuca scariola621250002409

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

Graminae

Poa annua

P. compressa

P. pratensis

Bromus inermis

B. carinatus

B. japonicus

Andropogon furcatus

Agropyron repens

Setaria lutescens

S. viridis

Leguminosae

Melilotus alba

Medicago sativa

Trifolium spp.

Gymnocladus dioica

Solanaceae

Solanum carolinense

Boraginaceae

Galium aparine

Caprifoliaceae

Lonicera japonica

Compositae

Lactuca scariola

Sonchus arvensis

Ambrosia trifida

A. artemisiifolia

Taraxacum officinale