The Mammals of Warren Woods, Berrien County, Michigan.
by Lee Raymond Dice.
Few detailed studies of the mammal a.s.sociations 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.
[Ill.u.s.tration: 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 b.u.t.tonbush 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 gra.s.s. 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 b.u.t.tonbush-swamp habitat Sh.o.r.e 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-gra.s.s 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 a.s.sociations is concerned, little dependence can be placed on studies made in that portion of the preserve. The gra.s.s 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 a.s.sistance 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.
NATURAL HABITATS
_Aquatic habitat_:
_Mustela vison mink._ Mink. Reported.
_Fiber zibethicus zibethicus._ Muskrat. Reported.
Mink and muskrat are reported by residents to occur in the Galien River in and near Warren Woods, but I was unable to secure any specimens though traps were set for them; neither did I see any signs of their presence.
_b.u.t.tonbush-swamp habitat_:
_Peromyscus leucopus noveboracensis._ Northern white-footed mouse. 8.
_Mus musculus musculus._ House mouse. 2.
A large b.u.t.tonbush swamp occurs in the preserve just south of the Galien River, but around this the native trees have been cut away and over its accessible edges it has been heavily pastured, so that it is not at all in its natural conditions, and it was not trapped. In the unpastured flood-plain north of the river there is another b.u.t.tonbush swamp of several hundred yards extent. This latter area was the one selected for study.
In this typical swamp the b.u.t.tonbush, _Cephalanthus occidentalis_, is practically the only plant present. It thickly covers the area with its tangled branches, which grow to heights of four to ten feet. The water had drained away in August, leaving the ground bare, though still wet and soft. Under the cover of the b.u.t.tonbush there is no herbage whatever, and upon the ground there are only a few decaying logs and a few small sticks, which often carry a light growth of moss.
Around the edges of this swamp there is a narrow belt of thick herbage, closely encroached upon by the typical forest of the flood-plain.
Fifty mouse traps set in this habitat took eight northern white-footed mice and two house mice the first night, August 5.
_Sh.o.r.e habitat_:
_Procyon lotor lotor._ Racc.o.o.n. Tracks.
_Peromyscus leucopus noveboracensis._ Northern white-footed mouse. 1.
Along the sh.o.r.es of the Galien River a narrow strip of bare ground was exposed in July and August. The ground of this strip is mostly mud, but in a few places it is sand or gravel. Usually the habitat is narrow, but in some places it is five to ten feet wide.
Tracks of racc.o.o.n were frequent on the sh.o.r.e along the river. From a few mouse traps set on the bare mud sh.o.r.e one northern white-footed mouse was taken August 4 beside a drift log.
_Mud-bar herbage habitat_:
_Peromyscus leucopus noveboracensis._ Northern white-footed mouse. 4.
A few small recently formed mud bars occur along the Galien River in its outer bends. These bars have not yet had time to become forested, and on their outer edges nearest the river there is usually no vegetation, this part being included in the sh.o.r.e habitat. On their older portions next the forest of the flood-plains occurs a thick growth of herbs, several annual gra.s.ses, and rarely a willow, _Salix_ sp., or a seedling tree of white elm, _Ulmus americana_, cottonwood, _Populus deltoides_, maple, _Acer rubrum_ or _saccharinum_, and others of the typical flood-plain species. The vegetation during August is very thick, and reaches a height of four to six feet. The soil is either mud or in a few places fine sand, and the ground is quite moist.
In this habitat four northern white-footed mice were trapped August 3-4.
_Flood-plain forest habitat_:
_Scalopus aquaticus machrinus._ Prairie mole. Ridges.
_Blarina brevicauda talpoides._ Short-tailed shrew. 4.