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Differential Effects of Coyotes and Red Foxes
on Duck Nest Success

Results


Seventeen of 36 areas were coyote areas, 13 were fox areas, and 6 were mixed-canid areas (Table 1). We found 840 duck nests; 803 met criteria for inclusion in analyses (471 in coyote areas, 211 in fox areas, 121 in mixed-canid areas). We found no difference in species composition of duck nests between coyote and fox areas (F = 1.81; 5, 20 df; P = 0.16) and no canid-year interaction (F = 1.22; 10, 40 df; P = 0.31). On coyote and fox areas combined 46% of nests were blue-winged teal, 27% gadwall, 14% mallard, 5% northern shoveler, 4% northern pintail, and 4% other species.

Table 1.  Number of nests and percent nest success for individual study areas that were occupied predominantly by coyotes, by red foxes, or by both coyotes and red foxes in North Dakota (1990-91) and South Dakota (1992) and least-squares meansa estimates of annual and overall nest success (95% CIb in parentheses).
  Coyote areas Fox areas Mixed-canid areas
Areas Nests % success Areas Nests % success Areas Nests % success
1990 1 13 21 (7-62) 1 19 39 (20-72) 1 24 6 (2-19)
2 14 45 (24-86) 2 12 26 (10-67) 2 11 50 (25-99)
3 12 43 (20-91) 3 19 29 (13-63)      
4 25 23 (11-49) 4 5 27 (6-100)      
5 19 57 (35-94) 5 22 12 (4-34)      
Annu. Mean of X   36 (28-45)     25 (19-32)     15 (9-23)
1991 6 9 58 (31-100) 6 9 12 (2-57) 3 60 54 (41-70)
7 24 62 (42-91) 7 23 19 (8-47) 4 4 56 (17-100)
8 53 29 (19-46) 8 6 15 (2-95) 5 15 19 (7-54)
9 61 27 (17-44)       6 7 9 (1-72)
10 9 61 (30-100)            
11 60 39 (27-57)            
Annu. Mean of X   37 (32-43)     16 (11-24)     43 (34-54)
1992 12 35 18 (9-36) 9 36 21 (11-40)      
13 14 36 (14-89) 10 13 15 (5-47)      
14 12 34 (14-81) 11 22 2 (0-9)      
15 61 22 (13-37) 12 13 10 (2-38)      
16 25 32 (17-62) 13 12 10 (2-49)      
17 25 33 (16-64)            
Annu. Mean of X   25 (21-30)     11 (9-15)      
Overall Mean of X     32 (25-40)     17 (11-25)     25 (13-47)
a Least-squares means estimate weighted by exposure days using GLM PROC statement (SAS Inst. Inc. 1990).

b 95% CI computed following Johnson (1979).

Nest Success

Daily survival rates of duck nests differed between coyote and fox areas (F = 9.63; 1, 24 df; P = 0.01). The average DSR was higher in coyote areas (0.967, SE = 0.003) than in fox areas (0.949, SE = 0.005). There were no year (F = 3.01; 2, 24 df; P = 0.07) and canid-year interaction (F = 0.54; 2, 24 df; P = 0.59) effects. The average DSR on mixed-canid areas (0.960, SE = 0.007) was intermediate between those estimated for coyote and fox areas, but small sample sizes precluded tests for variation. Mean overall nest success was 32% on coyote areas and 17% on fox areas, but varied among study areas (18-62% for coyote areas, 2-39% for fox areas) (Table 1).

Nest Failures

In coyote areas, 92% (208 of 226) of nest failure was attributed to predation and 8% (18 of 226) to abandonment without evidence of predation. On fox areas, 94% (136 of 145) of nest failure was attributed to predation, 6% (8 of 145) to abandonment without evidence of predation, and <1% (1 nest) to farm machinery.

Fifteen coyote areas and 10 fox areas had ≥10 large-clutch nests (totals of 443 and 179 large-clutch nests, respectively) suitable for estimating proportion (least-square means) depredated by foxes. The proportions of all large-clutch nests depredated by foxes were less for coyote areas (2%) than for fox areas (17%) (F = 14.0; 1, 23 df; P = 0.001). The proportions of all depredated large-clutch nests that were depredated by foxes were less for coyote areas (4%) than for fox areas (27%) (F = 14.1; 1, 23 df; P = 0.001).

Habitat Composition

We detected no difference in habitat composition between coyote and fox areas (F = 1.63; 4, 21 df; P = 0.20). The mean annual percent composition of habitat for coyote areas compared with fox areas was 47 versus 35% grassland, 26 versus 38% cropland, 8 versus 7% hayland, 16 versus 16% wetland, and 3 versus 4% right-of-way and farmstead, respectively.

Other Predators

Raccoons, striped skunks, badgers, and Franklin's ground squirrels were common in coyote and fox areas. Raccoons were detected in all areas, striped skunks in 11 of 17 coyote areas and 12 of 13 fox areas (χ² = 3.14, 1 df, P = 0.08), badgers in 11 of 17 coyote areas and 5 of 13 fox areas (χ² = 2.04, 1 df, P = 0.19), and Franklin's ground squirrels in 9 of 17 coyote areas and 3 of 13 fox areas (χ² = 2.74, 1 df, P = 0.10). Species detected less commonly were long-tailed weasels (in 3 coyote areas), and American crows and black-billed magpies (each in 3 coyote areas and 3 fox areas).


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