456 
for the recent decline in muskrat num- 
bers, which is associated with reduced 
range. 
1. Overtrapping, arising from demand 
for muskrat furs and resulting in insufh- 
cient breeding stock. 
2. Drainage of potential agricultural 
land, greatly reducing the aquatic habitat. 
3..Shortage of food, due to grazing, 
burning and clearing land. 
4. Predation, resulting largely from ex- 
posure of the animals during enforced mi- 
Fig. 15.—Three entrances to muskrat den in 
flooded stump, exposed by sudden drop in 
water level, Illinois River, Calhoun County. 
Muskrats may dig new tunnels to correspond 
with changes in water level. 
gration in search of water, and from a 
shortage of food and cover along streams 
and ditches. 
Habitats.—In Illinois, as elsewhere, 
trappers make a distinction between marsh 
and bank muskrats. Marsh muskrats, ex- 
cept along levees and banks, build houses 
of cattails, bulrushes, water smartweed 
and similar materials; bank muskrats sim- 
ply tunnel runways, beginning under water 
and ending above water. The marsh ani- 
mals are found principally in the northern 
half of the state, and along the Mississippi 
and Illinois rivers, fig. 7 and frontispiece. 
Bank muskrats inhabit drainage ditches, 
ponds and streams throughout Illinois, fig. 
8. In general, it appears that muskrats 
build houses if possible. Even in stripmine 
areas, where conditions favor bank dens, 
muskrats build an occasional house of 
cattail or other vegetation where its occur- 
rence 1s abundant enough and the area of 
shallow water large enough for the pur- 
pose (Yeager 1942). 
ILLINo1Is NATURAL History SURVEY BULLETIN 
Vol. 22, Arieo 
In the two seasons covered by this study, 
the greatest production of marsh muskrats 
came from the Glacial Lakes Region; the 
yield in this area averaged about 50 per 
square mile. “The Northwestern Sand 
Prairie produced about 25 per square mile, 
the Central Sand Prairie about 18 per 
square mile, table 6. 
Marsh muskrats occupy an environment 
which, under ideal conditions, is favored 
by relatively stable water levels and an 
abundance of vegetation (T'yphia, Scirpus, 
Polygonum and Potamogeton), fig. 14. 
Although the bank habitat is generally less 
favorable than the marsh habitat, the 
total catch of bank muskrats in Illinois 
exceeds that of the marsh animals. This 
is due to the much larger range inhabited 
by bank-dwelling animals, centering in the 
Black Prairie where streams and drain- 
age ditches afford extensive bank habita- 
tions. 
Muskrats show excellent adaptability to 
the changes and perversities of environ- 
ment, fig. 15. Food shortage, drought and 
flood occasionally decimate their numbers 
or force migration, but seldom extirpate 
them from a given stream or _ pond. 
Throughout the Black Prairie, thousands 
of shallow-water ditches offer, in normal 
seasons, habitats with sufficient food, water 
and cover, fig. 8. During wet years these 
ditches provide excellent range. ‘The catch 
varies by years, apparently according to 
weather conditions. In 1938-39 the total 
muskrat catch in the Black Prairie Re- 
gion averaged 28.23 per square mile; in 
1939-40, which was very dry over most 
of the region, the catch was only 18.51 
per square mile. 
Muskrat habitats in the Gray Prairie, 
the River Bluffs and Bottoms and the 
Western Prairie regions have low carry- 
ing capacities. “he intermittent character 
of the streams and general deficiency of 
aquatic vegetation, as well as heavy trap- 
ping, explain the comparatively low catch 
of about two to five animals per square 
mile, table 6. 
The quality or type of the habitat has 
considerable effect on the more obvious 
food habits of muskrats. The utilization 
of such items as willow, cottonwood, fish, 
mollusks and crustaceans seems to be more 
common among stream than among marsh 
muskrats, perhaps because of a shortage 
of cattails, bulrushes and similar vegeta- 
