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Effects of Predator Exclosure Design on Duck Brood Movements

Tables


Table 1. Specifications of ground-level exits for female ducks with broods in 3 predator exclosures in the prairie pothole region of North Dakota and Minnesota.
Design
type
Years Sitesa Openings Leads

height × length (cm)

nb height × width (cm)
1 1989 J 8 10 × 12c 91 × 122
2 1989 K 32 20 × 20 91 × 122
3 1990-1991 K 32 22 × 16 46 × 38
4 1990-1991 J, D 32 22 × 16 none
a Site J = Jamestown, N.D.; K = Kulm, N.D.; D = Detroit Lakes, Minn. In 1989, design 1 was installed at Detroit Lakes and Jamestown, but no data on brood exit times were gathered at Detroit Lakes.
b Number of pairs of exits in designs 1 and 2, single exits in designs 3 and 4.
c Size of opening was visually bisected into 2 smaller openings by a plexiglass flap (2.5 cm wide) that hung down on the outside of the exit.

Table 2. Time required for female mallards and gadwalls with broods to exit predator exclosures with different ground-level exit designs. Exit times were measured at 2 exclosures (near Kulm and Jamestown, N.D.) in 1989, and at 3 exclosures (near Kulm and Jamestown, N.D., and Detroit Lakes, Minn.) in 1990-1991.
Design
typea
Species Exit time (hr)b
n mean of x SE Range
1 Gadwall 6 3.2 2.0 0.1-12.4
2 Gadwall 9 0.6 0.1 0.2-1.0
3 Gadwall 13 2.0 0.9 0.1-10.0
4 Gadwall 21c 1.2 0.4 0.1-6.6
3 Mallard 6 3.2 1.3 0.1-8.2
4 Mallard 10 4.4 1.6 0.1-13.9
a Design 1 = Jamestown exclosure, 1989; design 2 = Kulm, 1989; design 3 = Kulm, 1990-1991; design 4 = Jamestown and Detroit Lakes, 1990-1991.
b Exit time does not include travel from the nest to the exclosure fence.
c One exit time from Detroit Lakes, 20 from Jamestown.

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