September, 1943 Brown & YEAGER: 
the catch showed reduced populations in 
the River Bluffs and Bottoms, the Black 
Prairie and Gray Prairie regions. All 
other regions showed an increased catch. 
Drought during the fall of 1939 may be 
advanced as a reason for the decline in the 
Black Prairie and Gray Prairie regions. 
The cause or causes for the appreciable 
decline in the River Bluffs and Bottoms 
Region are not known, but they may be 
suggested by certain social and economic 
factors peculiar to the region. It is certain 
that this area bears a heavy trapping and 
fur hunting pressure. Reasons for in- 
creased catches in the northern and north- 
western parts of the state are likewise 
unknown. 
Habitats.—lllinois mink habitats are 
so variable that they range from glacial 
marshes in the northeastern part of the 
state to cypress swamps in the southern 
tip, figs. 21 and 22. It is doubtful which 
type of habitat offers the better range; the 
yield for Lake County averaged 2.73 
minks per square mile for the two seasons 
of the survey, and Union County, just 
north of the cypress swamps, averaged 
1.79 during the same period. The cypress 
swamps themselves would probably have 
shown a greater density in catch. 
The Lake County habitat is character- 
ized by marshes, shallow lakes of glacial 
origin, little timberland and large muskrat 
populations; Union County, by much 
heavy timber, numerous small creeks and 
springs, steep bluffs and a low muskrat 
population. The cypress swamps are even 
more heavily forested, but without blufts 
and muskrats, and with but few springs. 
Comparable populations in such widely 
diverse habitats, in addition to general 
distribution in every county in Illinois, 
indicate great adaptability in minks and 
suggest that the species may long remain 
one of the more important fur animals of 
the state. 
Ability to make use of almost any sort 
of cover in the vicinity of water gives the 
mink a great advantage over larger and 
more intolerant animals, such as the rac- 
coon, figs. 23 and 24. The shore lines 
of streams, fig. 23, lakes, ponds and marsh- 
es; small runs and ravines, fig. 24; drifts, 
windfalls, brush, timberland and slashings: 
all afford mink cover. In the Glacial 
Lakes Region, marshy shore lines, stream 
banks and muskrat houses provide cover 
SURVEY OF FurR RESOURCE 
475 
and denning areas. In the Gray Prairie 
Region, cattail-bordered mine ponds and 
small lakes, bogs and springs make up for 
the intermittent nature of the many small 
streams. In the vicinity of many of the 
ponds and springs there are thick slash- 
ings, the result of hasty logging of mine 
props, where a combination of brush, 
stump sprouts and second growth offers 
excellent mink cover. The Northwest 
Hills provide good forest cover and the 
Northwestern Sand Prairie contains con- 
siderable marsh area. Both regions have 
numerous small, permanent waterways; 
drainage ditches partly replace streams in 
the latter region. In the Black Prairie and 
Central Sand Prairie regions, lack of water 
is the greatest shortcoming; most of the 
streams and ditches, especially in dry years, 
are intermittent. During the fall of 1939 
the water shortage in these two regions 
Was serious, and probably accounts in part 
for the reduced mink yield. 
Along the Illinois River, many minks 
live on or near wooded islands, isolated 
by marsh and shallow water. They den 
chiefly in hollow tree bases, especially 
willows,. or in the ground, and in some 
cases muskrat trappers here are not aware 
of their presence, often in comparatively 
large numbers. 
Trapping and Hunting.—Approxi- 
mately 87 per cent of the Illinois mink 
catch was taken in traps during the two 
seasons of the survey. Many minks, espe- 
cially along the Illinois and Mississippi 
rivers and in the Glacial Lakes Region, 
were taken in connection with muskrat 
trapping. Nearly all such minks were 
caught without the use of bait, trappers 
taking advantage of the mink’s habit of 
traveling muskrat runs and entering musk- 
rat houses and dens. Most bait sets were 
in shallow water and therefore operative 
only during nonfreezing weather. Other 
sets were made on logs, in narrow ditches 
and runs, and at points along waterways 
where minks were likely to step. Nearly 
all of the catch in the Glacial Lakes, 
Northwest Hills, Black Prairie and the 
Northwestern Sand Prairie regions was 
made by trappers. 
About 13 per cent of the Illinois mink 
catch for the two seasons of the survey 
was by hunters. In the Central Sand 
Prairie in 1939-40, hunters accounted for 
58 per cent of the catch. In no other 
