A two-year study was conducted on drainage ditches
in a 13 square mile study area of the Buena Vista Marsh,
Portage County, Wisconsin, to determine what effect
channel maintenance by dredging has on the wildlife of
the area and on the wildlife habitat. A 3-mile section
of Ditch-3, dredged in 1967-68, was compared to an
adjacent 2-mile control section which was last dredged
in 1921. The dredging widened the channel an average
of 7.9 feet, eliminated meanders and pools, and created
a flat stream bottom of homogeneous structure. Silt
accumulation was absent in the control section but was
present in depths from 1 to J feet in the dredged
section after the spring run-off subsided. Sheet-water
covered a maximum of 4826 acres of the study area
during the spring of 1973 and 832 acres in 1974, a
decrease of 83 percent due to reduced amounts of
precipitation. This was accompanied by a waterfowl
breeding population of 5.4 ducks per square mile in
1973 and 2.6 per square mile in 1974, a reduction of
52 percent. The nearest edge of the sheet-water was
located an average of 87 feet from the dredged section
of the ditch and an average of 274 feet on the control
section. The dredging thus reduced the sheet-water on
the study area by 136 acres. Ground water levels were
5.16 inches lower on the area adjacent to the dredged
section when compared to a comparable area on the
control section. Fifty-one percent of the dabbling
ducks were found on sheet-water areas and 14 and 35
percent on ditches and stock ponds, respectively, in
1973. Waterfowl numbers decreased from 1455 in 1973
to 316 in 1974, while usage in 1974 was 52, 11, and
37 percent for sheet-water, ditches, and stock ponds,
respectively. Diving ducks did not decrease in
numbers and were found almost exclusively on the
deeper stock ponds. Nest predation was highest on the
ditch banks and the chief predator was the striped
skunk. The principal nesting species was the blue-winged
teal with an overall nesting success of 38
percent and 20 percent on the ditch banks. Teal
nests were located within 80 feet of water during incubation, but those nests adjacent to sheet-water
did. not retain this proximity by hatching time because
the sheet-water had disappeared. Ditches provided the
only available brood habitat. Waterfowl production
was 7.48 broods per mile of ditch in 1973, and 0.62
per mile in 1974. Twice as many broods utilized the
control section of the ditch as compared to the
dredged section in 1973. Waterfowl hunting opportunities were limited to the opening hours of the
season. The majority of the blue-winged teal migrated
prior to season's opening and those remaining were
quite accessible. Bunting success in 1973 was 0.63
birds per hunter. Accessibility to all ditches and
lack of any refuge decreases the amount of waterfowl
hunting opportunities. Vegetation was absent on the
ditch bank subsequent to the dredging operation and
on the dredged section now consists of grasses, a few
forbs and scattered dogwood and aspen plants. The
control section has a grass and forb ground cover with
abundant shrub growth consisting of pin cherry, aspen,
and dogwood. Trees of these species constitute 763
stems per acre and range from 0.8 to 6.2 inches d.b.h..
Non-game bird species were found to be fewer on the
dredged section of Ditch-3 than on the control section. Total species counted on the dredged section in 1973
was 8, while there were 18 species on the control
section. Comparable figures for 1974 were 9 and 15
for the dredged and control sections, respectively.
The number of species was found to be a better indicator
of habitat quality than total number of birds present.
Trapping of small mammals on the dredged section of
Ditch-3 showed the meadow vole to be the most prevalent
species during both years. The white-footed mouse was the most common mammal caught on the control section.
The control section also had the greatest diversity of
species on the ditch bank. The striped skunk was the
most common of the larger mammals caught on the ditch
banks. Others caught were raccoon, badger, and
Franklin ground squirrel. White-tailed deer used the
ditches as watering sites and were present on the
marsh with a density of 32 +/- 2 per square mile