Few detailed studies of the mammal associations of the forests of the
United States have been made. But if we are ever to know, for our
different species of mammals, the natural environments under which
their evolution and differentiation occurred, we must study and
describe their habitats and habitat limitations before all the native
areas in the country have been altered by the activities of mankind.
As a contribution to this subject the following paper is presented.
The Warren Woods are a state preserve under the Edward K. Warren
Foundation. They are located in Berrien County, Michigan, about three
miles north of Three Oaks. The preserve consists of about two hundred
acres, of which somewhat less than half is in clearing and the
remainder mostly covered by forest, much of it still nearly in its
primitive condition.
[Illustration: FIG. 1.--Sketch map of Warren Woods Preserve. The
distribution of the various mammal habitats is indicated.]
The topography is nearly level, though the area is cut by a number of
ravines draining to the Galien River, which flows through the
preserve. Along the river and in its bends there are moderate-sized
flood-plains.
On the flood-plains a few small buttonbush swamps occur; and along the
margins of the river a few freshly formed mud bars have not yet become
forested; but most of the flood-plains are covered by heavy forest.
The higher ground, except that in the clearing, is covered by heavy
beech-maple forest.
Several types of habitats are represented in the clearing: in a few of
the cleared ravines a thick growth of sedges and iris occurs; on the
higher ground small areas are dominated by rushes, other areas by
sedges, while the greater part is covered by grass. In parts of the
clearing blackberries and other shrubs have grown up to form thickets,
and in many places, especially along the edges of ravines,
second-growth trees of oak, maple, or beech grow in the thickets or
form small groves.
The mammal habitats found on the preserve may be listed as follows:
_Natural habitats_
Aquatic habitat
Buttonbush-swamp habitat
Shore habitat
Mud-bar herbage habitat
Flood-plain forest habitat
Beech-maple forest habitat
Aerial habitat
_Modified and artificial habitats_
Second-growth, forest and scrub habitat
Cleared-ravine sedge habitat
Cleared-upland rush habitat
Cleared-upland sedge habitat
Cleared-upland blue-grass habitat
Cultivated field habitat
Orchard habitat
Edificarian habitat
It is unfortunate that all of the area in clearing and about half of
the forested area on the preserve has been and is being heavily
pastured by cattle and horses. The presence of stock has changed the
native conditions so much that, so far as interpreting the primitive
mammal associations is concerned, little dependence can be placed on
studies made in that portion of the preserve. The grass and herbage is
extensively eaten off, and many of the shrubs and young trees eaten
or badly mutilated. Under the pastured forest little underbrush or
herbage remains, and the conditions are very poor for small mammals.
In all the forest, in the unpastured as well as in the pastured part,
a number of trees have been cut out in former years, and although no
trees are now being cut down, all the trees and branches which fall
are being cut up for firewood. This results in there being few logs
and little dead brush on the ground, and removes a favorite place for
small mammal nests and runways, as well as largely eliminating as
mammal food the insects and larvae which are dependent on decaying
wood. However, with the exception of the removal of the logs and of a
few trees, that part of the forest to the north of the river is still
in practically its native condition, and it shows no evidence of ever
having been pastured. It is thus a splendid place for the study of the
native faunal conditions.
Although the whole area in the preserve is small there are other areas
of adjoining forest along the Galien River, so that, for the smaller
mammals at least, the results of the study and trapping should
indicate the primitive habitat distribution. The relative abundance of
the different species, however, is probably much changed by the
decrease throughout the whole region of the carnivores, which have
been much hunted and trapped by man.
The mammals of Warren Woods were intensively studied by the author
from July 3 to September 3 in the summer of 1919. A camp was
maintained near the edge of the Woods, and by trapping and hunting
every effort was made to determine the mammal fauna of the preserve.
From one hundred to two hundred traps for small mammals and about
twenty traps for the larger species were kept constantly in operation.
A small amount of trapping was done in the fields and along the
roadsides immediately adjoining the Woods and a few records were
secured from the camp house.
The work was supported by the Michigan Geological and Biological Survey.
Dr. Alexander G. Ruthven directed the work and gave much assistance in
securing the needed collecting equipment. Much help was given by George
R. Fox, Director of the Warren Foundation, not only in getting to and
from the camp at the Woods and in numerous other courtesies, but also in
information about the Woods and about the mammals there. The plant
identifications were made by Mr. C. Billington.
The figures following the specific names in the lists of mammals from
each habitat indicate the number of individuals trapped, shot, or seen
and positively identified in that habitat.