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.