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between years with a low of 7.86 cm in 1983 to a high of
25.41 cm in 1987 (Table 6). The low mean late VOR
recorded in 1988, was due to the lack of rainfall caused by
the drought (Table 6). Mean early vegetation height
(49.97 cm) was significantly less than mean late height
(73.49 cm, t=2.828, df=8, P=0.02) (Table 6). As with the
VORs, there was less variation in the mean late height
than in the mean early height (Table 6).
  There was a significant relationship between early
vegetation VORs and early vegetation height (r=+0.862,
t=4.491, P=0.03), but not between late VORs and late
vegetation height (r=+0.567, t=1.920, P=0.10). As the
mean early vegetation VORs increase, the mean early
vegetation height increased.
  Based upon the differences between mean early and
late vegetation VORs and height, it is apparent that
heavy snow in some winters flattened and decreased
the quality of the vegetation available as residual nest-
ing cover the following spring.
  The mean early litter depth (3.0 cm) was greater than
the mean late litter depth (2.48 cm, t=2.648, df=8, P=0.03)
(Table 6). This relationship was consisted among years
(r=+0.893, t=5.251, P-0.001). It appears that the snow
pack, which flattened the residual vegetation (i.e. low-
ered mean early VORs and height), increased the mean
early litter depth. Decomposition of the dead residual
vegetation during the growing season reduced the mean
litter depth measured at the cessation of plant growth in
the early autumn (Table 6).
Duck Nesting
A total of 796 duck nests were found in WPAs during
1982-90 (Table 7). Blue-winged Teal comprised 63%,
Mallards 36%, and other species (Green-winged Teal,
Northern Shoveler and Ring-necked Duck) 1% of the
total nests found. Interestingly, three Ring-necked Duck
nests were found in upland nesting cover (Evrard et al.
1987). Ringnecks normally nest in aquatic vegetation
over or adjacent to water (Mendall 1958).
   In a 1977-81 nesting study in the Grand River Marsh
Wildlife Area in southern Wisconsin, Wheeler et al. (1984)
found that Blue-winged Teal comprised 84%, Mallards
10%, Gadwall 4%, and other ducks (Northern Shoveler,
American Wigeon, Northern Pintail, and Green-winged
Teal) 2% of 918 nests found. They reported an estimated
Blue-winged Teal nestfound while cable dragging.
mean density of 2.2 nests per acre using a nest searching
technique identical to this study. The mean nest density
estimated in this study was considerably lower (0.14
nests/acre) despite nearly identical breeding pair esti-
mates (i.e. 73.0 pairs/mi2 in Wheeler et al. 1984 and 68.4
pairs/mi2 in this study). An explanation may be the nest-
ing cover in the Grand River Marsh Wildlife Area was con-
centrated around one large wetland (Wheeler et al. 1984)
while nesting cover in this study surrounded many small
wetlands widely dispersed throughout the study area.
Nest Characteristics
The mean VOR at 291 Mallard nests (36.1 cm) was signif-
icantly greater than the mean VOR at 534 Blue-winged
Teal nests (24.9 cm, t=10.887, df=9, P=0.000002). With
these preferences and the very strong relationship that
exists between the single vegetation height measurement
and the mean of eight VOR vegetation measurements at
each nest (r=+0.919, t=8.746, P=0.000001), it is apparent
that Mallards in this study and other studies (Schranck
1966, Fleskes, 1986, Glup 1987) prefer to nest in taller,
denser vegetation than Blue-winged Teal. Duebbert and
Lokemoen (1980) found that 98% of 499 Mallard nests
were found in cover that exceeded 30.5 cm in height.
Livezey (1981b) found the mean height at Mallard nests to
be 18+1 cm and 15+1 cm for Blue-winged Teal in retired
croplands in the Horicon National Wildlife Refuge.
Lokemoen et al. (1990) found higher Mallard nest densi-
ties in tall and dense cover (with greater VORs) while
Blue-winged Teal selected shorter cover nearer to water.
In an Iowa study, the mean VOR at Mallard nests was 34.0
cm, significantly greater than the mean VOR of 24.9 cm at
Blue-winged Teal nests (Fleskes and Klaas 1991). Shaffer
et al. (1985) in a study of 15 areas in North Dakota,
Saskatchewan, and Manitoba suggested that Blue-winged
Teal do not nest in fields where the VOR is <20.32 cm in
the early spring.
  In this study, dominant plant species at Mallard nests
was Switchgrass (36%) and Bromegrass (30%) with other
grasses (11%) and forbs (16%) making up the balance of
the vegetation. This was residual vegetation from the pre-
vious growing season. Glup (1987), in an Iowa study,
found that Mallards were more frequently found in
Switchgrass.
Blue-winged Teal nesting in dense cover.
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